Review Article Photocatalytic Based Degradation Processes of...

Review ArticlePhotocatalytic Based Degradation Processesof Lignin Derivatives

Colin Awungacha Lekelefac1 Nadine Busse1 Michael Herrenbauer2 and Peter Czermak134

1 Institute of Bioprocess Engineering and Pharmaceutical Technology University of Applied Sciences Mittelhessen35390 Giessen Germany2Media University Packaging Technology 70569 Stuttgart Germany3Department of Chemical Engineering Faculty of Engineering Kansas State University Manhattan KS 66506 USA4Faculty of Biology and Chemistry Justus-Liebig-University Giessen 35392 Giessen Germany

Correspondence should be addressed to Peter Czermak peterczermakkmubthmde

Received 8 August 2014 Accepted 13 October 2014

Academic Editor Elisa Isabel Garcia-Lopez

Copyright copy 2015 Colin Awungacha Lekelefac et al This is an open access article distributed under the Creative CommonsAttribution License which permits unrestricted use distribution and reproduction in any medium provided the original work isproperly cited

Photocatalysis belonging to the advanced oxidation processes (AOPs) is a potential new transformation technology for ligninderivatives to value added products (eg phenol benzene toluene and xylene) Moreover lignin represents the only viable sourceto produce aromatic compounds as fossil fuel alternative This review covers recent advancement made in the photochemicaltransformation of industrial lignins It starts with the photochemical reaction principle followed by results obtained by varyingprocess parameters In this context influences of photocatalysts metal ions additives lignin concentration and illuminationintensity and the influence of pH are presented and discussed Furthermore an overview is given on several used process analyticalmethods describing the results obtained from the degradation of lignin derivatives Finally a promising concept by couplingphotocatalysis with a consecutive biocatalytic process was briefly reviewed

1 Introduction

In October 2014 the price of crude oil was 85 dollars perbarrel and the forecast for next year is 98 dollars per barrel [1]This is a symbolic indicator for the decreasing availability ofconventional nonrenewable energy sources due to the globaleconomy growth coupled with frequent political instabilityAccording to the World Energy Technology and ClimatePolicy Outlook of the European Commission [2] the worldtotal energy consumption levels will rise from 121 times 109 tonsoil equivalent (toe) (2010) to 145 times 109 toe (2020) to 171 times109 toe by 2030As a result theworld carbondioxide emissionfrom the combustion of fossil fuels will increase from 293 times109 tons (2010) to 367 times109 tons (2020) to 445 times 109tons (2030) That means the world carbon dioxide emissionwill be almost doubled by 2030 Also less than 1 of the300 times 106 tons of plastic produced per year are natural

polymers [3] Thus there is a need for the developmentof biobased macromolecular materials which would reducethe consumption of fossil resources and hence reduce CO

2

emissionThe major option is a gradual replacement of these fossil

resources by renewable alternatives for example wind sunwater and biomass Ligneous biomass also known as ligno-cellulosic biomass is of great interest for industries (chem-istry biotechnology and fuel) and biorefineries convertingsustainable materials [5] This is due to the biomassrsquos highvalue-added compounds cellulose (40ndash50) hemicellulose(24ndash35) and lignin (18ndash35) [6] Furthermore biomassis inexpensive and available in large amounts [7] as wellas being CO

2neutral [8] Nevertheless just 3ndash35 of the

yearly produced biomass (170ndash200 times 109 tons) is utilized bynonfood applications [5] because of reasons related to thelignocellulosic structure per se and its processability

Hindawi Publishing CorporationInternational Journal of PhotoenergyVolume 2015 Article ID 137634 18 pageshttpdxdoiorg1011552015137634

2 International Journal of Photoenergy

Cellulosehemicellulose

lignin

Biomass

Pretreatment

Pyrolysis andgasification

Platformchemicals

Step 1

1

2

3

Step 2catalysis

Catalysis

Syngas

Furtherprocessing

catalysis

New technology

New technology

Current technology

Lignin

Cellulose

Hemicellulose

Fuelsbulk and fine

chemicals

PhenolBenzene Toluene Xylene

ProteinsLipidsAsh

SoilSaltsWater

KraftSulfiteOrganosolvPyrolysisSteamExplosionAFEXHot waterOther

For example Fischer-Tropsch methanol synthesis

COH2

OH

OH

OH

OH

OH

R R

ROH

OH

OH

OH

OH

OH

OH

O

OOO

HO

HO

O O

O

Figure 1 Lignocellulosic biorefinery scheme with particular emphasis on the lignin stream reprinted with permission from Zakzeski et al[4] copyright (2010) American Chemical Society

Figure 1 depicts an exemplary lignocellulosic biorefineryscheme with emphasis on the lignin stream For separa-tion purposes several pretreatment procedures are currentlyapplied in order to generate lignin derivatives (modificationin lignin structure) which can be differentiated on thebasis of their isolation method and their origin since theirphysical and chemical properties differ [9ndash11] The mostindustrialtechnical lignins (gt70 million tons per year) areobtained as waste material by the pulp and paper industry[12] mainly from the kraft process as noted by Kamm etal [5] 98 is burnt for energy recovery in the paper mills[13] while less than 2 is sold primarily in formulationof dispersants adhesives and surfactants [14] Lignin is anaromatic biopolymer of high potential fission products fora wide range of sectors and it is thus gaining attention forexample for the production of platform chemicals (Figure 1)Nonetheless lignin is still underutilized and fundamentalresearch and development are needed [5]This is explained byligninrsquos complex nature its recalcitrance to degradation andthe difficulty to analyze its numerous degradation productsTherefore intensive research goes on both sides processengineering and development (homogeneous heterogeneouscatalysis thermal electrochemical andor hybrid proce-dures) and process analytics

Photocatalysis is an advanced oxidation process (AOPs)[15] with the potential to transform lignin to value addedproducts such as phenol benzene toluene and xylene [4]In this context it can be applicable as stand-alone unit or it

can be coupledwith otherAOPs (eg Fentonrsquos reagent ozoneelectrochemical oxidation) as well as biocatalysis [15] (eghydrolysis through ligninolytic enzymes)

This paper is aimed at reviewing photocatalysis of indus-trial lignins in connection with evaluating the effects ofbasic operating parameters such as catalyst loading illu-mination intensity integration of metal ions and otheradditives pH and initial lignin concentration Furthermoreanalytical techniques used by different researchers are dis-cussed Finally a brief overview concerning the suitabilityof photocatalysis as a pretreatment method for subsequentbiocatalysis by ligninolytic systems for example fungal hemeperoxidases andor laccases is highlighted

2 Lignin as Raw MaterialChemical Structure and Sources

Lignin is the only naturally synthesized aromatic biopolymer[16] and after cellulose themost abundant renewable carbonsource on earth [17] In addition native lignin is a poly-disperse 3D macromolecule with an undefined molecularmass The biopolymer is made up of randomly arrangedphenylpropane units 119901-coumaryl alcohol coniferyl alcoholand sinapyl alcohol as depicted in Figure 2 contributing to anirregular structure [11]

An overview of the common interunit linkages and itsestimated proportions are shown in Table 1 For a better

International Journal of Photoenergy 3

1

2

3

45

120572120573

120574OH

OH

p-Coumaryl alcohol

OCH3

OH

OH

Coniferyl alcohol Sinapyl alcohol

OCH3H3CO

OH

OH

Figure 2 Monomer structures of lignin [18]

Table 1 Overview of most frequent bond types found in lignin

Model linkagea W G Glasser and H R Glasser [19] Erickson et al [20] Nimz [21]120573-Carbon-oxygen-4-aromatic carbon 55 49ndash51 65120572-Carbon-oxygen-4-aromatic carbon mdash 6ndash8 mdash120573-Carbon-5-aromatic carbon 16 9ndash15 6120573-Carbon-1-aromatic carbon 9 2 155-Aromatic-carbon-5-aromatic carbon 9 95 234-Aromatic-carbon-5-aromatic carbon 3 35 15120573-Carbon-120573-carbon 2 2 55120573-Carbon-120573-carbon forming furanic structure mdash mdash 2120572-Carbon-120574-carbon-oxygen-120574-carbon 10 mdash mdasha of total phenylpropane units

illustration Figure 3 shows the structure of a softwood ligninfragment containing all prominent linkage types

Native lignin cannot yet be isolated Contrary manymodified lignins of great variety are available throughbiomass transformation technologies [17] Depending onthe used isolation method lignosulfonate alkali lignin sul-fate lignin hydrolytic lignin steam exploded lignin andorganosolv lignins can be derived [31] The kraft and sodapulping processes generate liquors referred to as black liquorcontaining alkali lignin also called kraft or sulfate lignin [31]Although the kraft process is the dominant process (89)lignosulfonates attract more attention for the application oflignin as industrial products This is probably because ofadvantages such as its solubility properties and relativelylower mass range Moreover lignosulfonates are the onlycommercial lignins which are water soluble Their averagemolecular weight varies from 400Da up to 150 kDa or even17000 kDa (taken from Goring [9]) determined by processconditions and applied analytical methods [11]

3 Photocatalysis of Lignin

In this section the reaction principle for the photocatalyticdegradation of lignin is described After that themost impor-tant operating parameters and their impacts are discussed

31 On the Reaction Pathways for Photocatalytic Lignin Degra-dation Photocatalysis is the acceleration of a photoreactionin the presence of a catalyst In other words it involves theinitial absorption of photons by a molecule or substrate toproduce highly reactive electronically excited states

Lignin degradation is generally in the range of lowerenergy (between 300 and 400 nm) because of its multifunc-tional character [32ndash34]This region falls within the UV-lightregion TiO

2is the most applied photocatalyst and its energy

band gap is approximately 32 eV [35]In photogenerated catalysis the photocatalytic activity

depends on the ability of the catalyst to create electron-hole pair which generates free radicals (eg hydroxyl radi-cals ∙OH) enabling secondary reactions [36] Other aspectsinclude the rate of electron transfer the rate of chargerecombination crystal structure surface area of catalystporosity and surface hydroxyl group density [37]

In what follows equations summarizing the formationof radical species under photocatalytic conditions shall bedescribed S stands for the lignin substrate while TiO

2(h+VB)

and TiO2(eminusCB) represent the electron deficient (valence

band) and electron-rich (conduction band) parts in thestructure of TiO

2 respectively

The initial photocatalytic process involves the generationof electron-hole pair in the semiconductor particles as a result


Spirodienone

O

OO

O

O

OHO

OO

O

O

O

O

OHO

O

O

O

O

O

O

OO O

O

O

O

O

O

O

O

OH

OO

OO

O

O

OO

p-Coumarylalcohol fragment

Coniferylalcohol fragment

Branching caused bydibenzodioxin linkage Phenylcoumaran

HO

OAr

HO

OH

OHOH

OH

HO

HO

OH

HO

OH

HO

OH

HO

OH

HO

OH

HO

OH

HO

OH

HO

OH

HO4-O-5

OH

HOOH

120573-120573

5-5998400

120573-O-4

120573-1

120573-1

O

Figure 3 Structure of a softwood lignin fragment showing the prominent linkage types reprinted with permission from Zakzeski et al [4]and Evtuguin et al [22]

O2∙minus + H+ HO2

∙

2HO2∙

HO∙ + OHminus

∙OH

S + HO∙ S∙+ + OHminus

S∙+ + O2SO2

∙+

O2∙minus

∙O2minus

∙OH (hydroxyl radical)

(a) Reduction of O2H2O2

O2 + eminus

H2O2 + O2

H2O2 + eminus

(b) Oxidation of substrate

h+ + OHminus

Electron capture

Recombination

eminus

h+

Conduction band

Valence band

Electron release

eminus

O2

(super oxide)

Light

OHminus

Figure 4 Photocatalysis principle adapted from Linsebigler et al [23]

of UV radiation [38 39] Figure 4 shows the excitation ofan electron from the valence band to the conduction bandinitiated by light absorption with energy equal to or greaterthan the band gap of the semiconductor This is expressed by(1)

Upon excitation the fate of the separated electron andhole can follow several pathways Electron or holes canthen react with hydroxyl ions (OHminus) or H

2O producing

hydroxyl radicals (∙OH) as shown in (2) Jaeger and Bard[40] Matthews [41] andMachado et al [42] report that ∙OHis the main oxidizing agent in the photocatalytic oxidationbecause of the unpaired electrons Therefore it can react fastand unspecifically with almost all organic compounds (S)

[43] abstracting an electron with the formation of a radicalorganic species as shown in (3) [44]

Formation of singlet oxygen hydroxyl and superoxideradicals as principal reactive species in a photocatalyticprocess [38 39] is as follows

TiO2

ℎV997888997888rarr TiO

2(

eminusCBh+VB) (1)

TiO2(h+) +H

2O 997888rarr TiO

2+HO∙ +H+ (2)

S +HO∙ 997888rarr S∙+ +OHminus (3)


MeO MeOMeOMeO

∙OO

O

O ∙

OH

HO+ +

Figure 5 Formation of phenoxyl radicals by intermolecular abstraction of phenolic hydrogen by carbonyl groups

RH

bond cleavage

Vanillin

O

OO

O

OO O

O

O

O

O

O

HO HO

HOHO

HO

HO

HO HO

OH OH

HO

OCH3

OCH3

OCH3

OCH3

OCH3 OCH3

OCH3

OCH3 OCH3

OCH3

h minusH∙OH∙∙

O2TiO2

HminusOH∙

C120572-C120573

∙

Figure 6 Supposed lignin degradation scheme by autoxidation induced by TiO2poly (ethylene oxide) [24]

S∙+ +O2997888rarr SO

2

∙+ (4)

TiO2(h+) + S 997888rarr TiO

2+∙S+ (5)

TiO2(eminus) +O

2997888rarr TiO

2+∙O2

minus (6)

HO∙ + ∙O2

minus

997888rarr OHminus + 1O2

(7)

TiO2(eminus) + TiO

2(h+) 997888rarr heat (8)

The organic radicals and radical cations can for examplereact with molecular oxygen to form organic peroxy radicalsand peroxy radical cations respectively (4) The holes canoxidize organic compounds by electron abstraction to formorganic cationic radicals (5) [42] Superoxides can be formedby the reaction of electrons with electron acceptors suchas O2(6) Meanwhile the formation of singlet oxygen can

be from the reaction of hydroxyl radical and superoxide(7) [42] Moreover there is a possibility that electrons andholes recombine if electron acceptors are limited In thiscase recombination can take place in the volume of thesemiconductor particle When recombination takes placeradiation energy is lost or converted into heat (8) [45]

From investigations caried out by Mazellier et al [46](photochemistry of 26-dimethylphenol) it was postulatedthat hydrogen can be abstracted by 120572-carbonyl groups In thesame context lignin derivatives having similar functionalitycan follow a similar pathway In addition oxidative chainreactions with the participation of ground-state oxygencan be initiated leading to fragmentation and combinationreactions and thus the formation of new dimers or oligomers(Figure 5)

Miyata et al [24] proposed a cleavage mechanism forthe C120572ndashC120573 bonds which leads to the formation of smallfragments such as vanillin as shown in Figure 6

Figure 7 [25] illustrates the formation of a radical cationformed as a result of enzyme (lipase) mediated reactionof adlerol Adlerol is characterized by a C120573ndashOndash4 bondand considered to be a lignin model compound With theformation of the radical species subsequent nonenzymaticreactions such as radical reactions can take place generatinga wide variety of products and complex compounds

It is widely assumed that the photocatalytic degradationof lignin follows a radical reaction pathwaywhich is similar tothat considered in thermal electrochemical and biochemical


Nonenzymatic subsequent reactions

Adlerol

Veratryl alcohol radical

Enzyme1

23

4

4

1

2

3

5

5

6

6

Guaiacol

Veratraldehyde

Ketone

O

OO

O

O O

O

O

O

HO

HOHO

HO

OCH3

OCH3

OCH3

OCH3

OCH3

OCH3

120572120573

120574

minusH+

∙+

∙

∙+

c120572 oxidation H2O

O2

120572 120573

120574

HOHOHO

OCH3

OCH3OCH3

OCH3 OCH3

OCH3

OCH3

120572120572

120573 120573

120573

120574 120574

HO

HO

120574

OCH3

120573

HO

HO

120574

HO

OCH3

OCH3

OCH3

120572120573

120574

Figure 7 Proposed radical reaction scheme initiated by enzyme lignolytic heme peroxidase for the conversion of adlerol possessing C120573ndashOndash4 bonds into smaller units summarized by Busse et al [25] and abstracted from Tien and Kirk [26] Kirk et al [27] Lundell et al [28]Schoemaker et al [29] and Palmer et al [30]

processes However reporting on the degradation pathway oflignin derivatives and even that of lignin model compoundsis still a major challenge This is probably due to the complexnature and variety of possible degradation products Indeedthemechanism is far more complex considering other factorssuch as type of lignin type of catalyst pH illuminationsource and additives

32 Influence of Process Parameters in Lignin DegradationVarying process parameter could either have a positive ornegative impact on the photocatalytic efficiency The basicprocess parameters such as catalyst concentration [4 4856] substrate concentration [48 51] addition of metal ion

to TiO2catalyst [17 50 56ndash58] pH [47 48] illumination

[33 48 49 59] and their influence shall be discussed in thissubchapter Table 2 gives an overview about starting reactionconditions and catalyst applied by some work groups whileTable 3 portrays parameters analytical methods and resultsobtained It is worthwhile noting that comparing the differentphotochemical processes poses a big challenge because ofthe wide variables involvedThese discrepancies start alreadyfrom the source and type of lignin followed by the differencesin reactor design illumination source intensity of radiationand different types of TiO

2catalyst such as Fischer scientific

rutile TiO2[49] TiO

2(TiO2mdashTP-2 of Fujititan) just to name

a few


Table2Summaryof

startingcond

ition

sfor

thep

hotocatalytic

degradationof

lignin

Reference

Lign

insource

Catalyst

Reactio

ncond

ition

s

MacHadoetal[42]

Peroxyform

icacid

lignins

from

eucalyptus

grandisw

ood(EL1)

EL1+

sodium

borohydride

TiO

2andH

2O2

Lign

inconcentration

025

mgmL119879=25∘C

pH11U

VVisradiatio

n120582gt300nm

40

0Wmercury

lampcylin

dricalPy

rexglassreactorcon

stanto

xygenbu

bblin

g

Ksibietal[47]

Water

solubleligninob

tained

from

blackliq

uor

TiO

2-P2

5(D

egussa)

Lign

inconcentration

90mgL119879=20∘C

pH82UV-radiation120582gt290nm

pyrex

reactoro

pento

airPh

ilips

HPK

125W

lamp

Kansaletal[48]

Lign

infro

mwheatstr

awkraft

digestion

TiO

2-P2

5(D

egussa)a

ndZn

O

Lign

inconcentration

10ndash100

mgLin

100m

LZn

Ocatalystdo

se(05ndash20gL)pH

ofthes

olution(pH3ndash11)solarillu

mination

oxidantcon

centratio

n306times10minus6M

to153times10minus6Mthinbedfilm

slurrypo

ndreactoroxidantsodium

hypo

chlorite

solutio

n(4availableC

l 2)

Dahm

andLu

cia[

49]

Whitewater

from

indu

strialprocess

water

thatexits

inpaperm

achines

FischerS

cientifi

crutile

TiO

2

Lign

inconcentration

40mgLin

500m

Lbatchreactor119879=21∘Cndash

42∘C

Rayonet

photochemicalcham

ber16

VWR8-W

blacklightpho

spho

r(350-nm

)lam

ps

constant

oxygen

bubb

lingpo

wer

ofillum

ination

128to

64Wlight

intensity

223ndash44

5mWcm

3

Portjanskajaand

Preis[50]

Lign

inpurchased

from

Aldric

hTiO

2P2

5-N(D

egussa)

Lign

inconcentration

100m

gLpH

8batchreactorsystemreactor

open

toair

PhillipsT

LD15W05low-pressurelum

inescent

mercury

UV-lampUV-radiation

120582gt360nm

pow

erdensity

ofirr

adiatio

n=07m

Wcm

2 visib

lelight

source

Tanaka

etal[51]

Lign

infro

mconiferous

woo

dTiO

2(TiO

2mdashTP

-2of

Fujititan)

Lign

inconcentration

0003to

003U

V-radiation120582gt310nm

cylindrical

reactio

nvessel

Tonu

ccietal[33]

Ca2+andNH4

+ligninderiv

atives

TiO

2as

Degussa

P25

+po

lyoxom

etalates

(POM)H

2O2

Openqu

artztubes(20

mL)

reactor119879=20∘C

1atm

multirayso

ften

UVlamps

of15W

power

eachU


Miyatae

tal[24]

Piceag

lehn

iiwoo

dflo

urTiO

2po

lyethylene

oxide(PE

O)

Reactorop

enpetrid

ish119879=30∘C119905=48h40

0Wmercury

lamp

Shende

etal[17]

Kraft

lignin

TiO

2-Zn

O-ZrO

2Lign

inconcentration

1mgmLin

10mL250W

Xeno

nlampandAM

15Glamp

filterpo

wer

density

ofirr

adiatio

n100m

Wcm

2 solarlam

psim

ulator

Tian

etal[52]

andPanetal[53]

Kraft

ligninfro

mblackliq

uor

Ta2O

5-IrO

2andPb

O2thin

film

TiO

2nano

tubePbO

2

Lign

inconcentration

30(w

w)UV-radiation120582gt365nm

119905=10minpow

erdensity

ofirr

adiatio

n20

mWcm

2 blue

waveT

M50

ASUVspot

lampEG

ampG2273

potentiosta

tgalvano

stattoapplycurrentTiTiO

2NTPb

O2ele

ctrode

asworking

electrode

andPt

coilas

outere

lectrode

andAgAgC

lasreference

electrode

Awun

gachaL

ekele

fac

etal[54][55]

Lign

insulfo

natefro

mpaperw

aste

water

TiO

2as

Degussa

P25

TiO

2fro

msol-g

elprocesso

fTiOSO

4TT

IP

Lign

inconcentration

500m

gLin

200m

LOsram

Planon

light

sourceirradiance

30ndash4

0Wm

2 UV-radiation120582280ndash4

20nm

119905=20hreactoro

pento

air

recirculationsyste

mflow

rate225mLmin


Table3Parametersanalyticalmetho

dsand

results

from

different

workgrou

ps

Reference

Parameter

studied

Analytic

sRe

sult

MacHado

etal[42]

Roleof

hydroxylradicals

irradiatio

nof

ligninin

the

absencea

ndpresence

ofph

otocatalystT

iO2andH

2O2

Ultraviolet-v

isible(UV-Vis)spectro

scop

yionizatio

nabsorptio

nspectro

scop

y(IA

S)

sizee

xclusio

nchromatograph

y(SEC

)

Asharpdecrease

inthep

heno

liccontento

bservedforreactions

involvingdirect

photolysis

SEC

areductio

nof

almost50

inthea

verage

molecular

weighto

fligninequalto

14kD

after

90min

ofirr

adiatio

n

Ksibietal[47]

Irradiationof

ligninin

the

absencea

ndpresence

ofph

otocatalystT

iO2-P2

5

UV-Visspectroscop

y13C-

nucle

armagnetic

resonance(NMR)

solid

state

totalion

gasc

hrom

atograph

y(TIC)

indu

ctioncoup

lingplasma(

ICP)

chem

icaloxygen

demand(C

OD)

56degradationratewith

TiO

2catalystaft

er420m

inreactiontim

eethylacetate-extractableprod

uctsshow

edvanillin

vanillica

cidpalm

itica

cid

biph

enylstructuresand

345-trim

etho

xybenzaldehyde

presence

ofmagnesiu

mandcalcium

ions

CODremovalishigh

erforthe

initiallylowconcentrations

ofligninsolutio

n

Kansaletal[48]

Catalystdo

sepHoxidant

concentration

initialsubstrate

concentration

ZnOcatalystin

slurryandim

mob

ilizedmod

e

UV-Visspectroscop

yCO

D

Optim

umcatalystdo

seis1gL

optim

umoxidantcon

centratio

n2times10minus6M

graduald

ecreaseo

fabsorptionpeak

indicatin

gdecompo

sitionof

organics

CODremovalishigh

erforthe


ofligninsolutio

n

Dahm

and

Lucia[

49]

Catalystdo

seillu

mination

intensity

UV-Visspectroscop

ytotalorganiccarbon

(TOC)

capillaryionelectro

phoresis

analysis(C

IA)

Gradu

aldecrease

inabsorptio

npeak

indicatin

gdecompo

sitionof

organics

optim

alcatalystdo

seof

10mgm

high

erillum

inationintensities

correlated

well

with

high

erinitialdegradationrate

74disapp

earanceo

fTOC

Portjanskajaand

Preis[50]

Influ

ence

offerrou

sion

sN-dop

edcatalysteffect

sprayedcatalyston

supp

ortand

subm

ersedcatalyst

CODU

V-Visspectroscop

ybiochemical

oxygen

demand(BOD)colorim

etric

measurementat570

nm

Additio

nof

Fe2+upto

28m

gLleadsto25increase

inph

otocatalyticeffi

ciency

sprayedcatalystexhibited15

times

high

ereffi

ciency

than

theo

neattached

bysubm

ersio

nnegligibleeffecto

fN-dop

edcatalyst

increase

ofaldehyde

concentrationover

reactio

ntim

eneutralm

ediawas

mostb

eneficialforb

iodegradability

80of

freep

heno

lsremoved

undern

eutralcond

ition

s

Tanaka

etal[51]Ca

talystloadinglignin

concentration

illum

inationtim

e

UV-Visspectroscop

yTO

Cgel

perm

eatio

nchromatograph

y(G

PC)

1 HNMR

Fouriertransform

ationinfrared

(FTIR)

spectro

scop

y

FTIR

measurementrevealedafasttransform

ationof

arom

aticmoietyp

resent

inlignin

characteris

ticband

sofaromaticrin

gsm

etho

xyand

aliphatic

sidec

hains

decrease

inTO

Cvalues

over

time

decrease

indegradationratewith

increase

catalystdo

sageB

utaft

ercatalystthreshold

valueisa

ttainedcatalystincreasec

ausesa

decrease

indegradationrates

FTIR

peaksa

reshifted

towards

lower

molecular

weightregionaft

erph

otocatalysis

Tonu

cci

etal[33]

Testof

catalytic

syste

mstoob

tain

fractio

nswith

redu

ceddegreeso

fpo

lymerization

comparis

onof

thermalandph

otochemical

reactio

ns

1 HNMR

gasc

hrom

atograph

y-mass

spectro

scop

y(G

C-MS)

POMsa

relessselectivew

henused

asph

otocatalystsandno

appreciableb

leaching

ofthes

olutionwas

seen

whenPO

Mwas

used

asthermalcatalyst

deriv

edchem

icalsfrom

experim

entvanillin

hydroxylmetho

xy-acetoph

enon

econiferylalcoh

olcon

iferylaldehydemethano

lform

icacidacetic

acidand

sometim

essm

allamou

ntso

fC-2

andC-

3alcoho

ls

Miyatae

tal[24]

Exam

inationof

cellwall

structureo

flignin(w

oodflo

ur)

before

andaft

erph

otocatalysis

GC-

MSscanning

electronmicroscop

y(SEM

)1 H

NMR

Highdelignificationactiv

itydelignificationconfi

nedto

thes

urface

oflignin

deriv

edchem

icalse

xperim

entvanillin

Shende

etal[17]Testof

combinedactio

nof

bio-

andph

otocatalyticsyste

ms

UV-Visspectroscop

yGC-

MSX-

ray

dispersiv

eenergyspectro

scop

yandX-

ray

diffractio

nanalysis(EDX

XRD)SE

M

Detectio

nof

follo

wingchem

icalsacetylguaiacol4-ethoxym

ethyl-2

-metho

xyph

enol

metho

xyph

enyloxim

eguaiacolsuccinica

cidacetylguaiacolvanillicacidand

vanillin


Table3Con

tinued

Reference

Parameter

studied

Analytic

sRe

sult

Tian

etal[52]

andPanetal

[53]

Testof

combinedactio

nof

electro-and

photocatalytic

syste

ms

UV-Visspectroscop

yFT

IRSEM

X-ray

(EDX)

highperfo

rmance

liquid

chromatograph

y(H

PLC)

COD

Detectio

nof

thefollowingchem

icalscarbon

ylfunctio

nalityvanillin

andvanillica

cid

Awun

gacha

Lekeleface

tal

[54][55]

Com

paris

onof

degradationrates

bydifferent

catalyst

HPL

Cflu

orescencea

ndUV-Vis

spectro

scop

ySE

MT

OC

UV-Visresultsrevealfaste

rdegradatio

nof

thea

liphatic

moietycomparedto

the

arom

aticmoietyof

ligninsulfonateob

tained

from

paperw

astewaterPeaks

observed

durin

gHPL

Canalysis

Someo

fthe

peaksp

rodu

cedaft

erph

otocatalysishad

fluorescences

ignals

Thissuggeststhep

rodu

ctionof

newsubstances

andflu

orop

hores

Coatin

gsprod

uced

throug

hSol-G

elprocedures

arestablea

ndcanbe

used

manytim

es


321 Influence of Catalyst One aspect to successfully imple-ment photocatalysis is the choice of an appropriate photo-catalyst The majority of catalysts used are based on TiO

2as

summarized in Table 2 ZnO has also been applied either assingle catalyst [48] or in a combination with other catalystsuch as TiO

2[54] de Lasa et al [60] described ZnO as

being less active than TiO2 They add that the use of ZnO

is particularly relevant when the oxidative degradation ratebecomes limited This is opposite to what Kansal et al [48]reported by saying that ZnO is more reactive than TiO

2

However TiO2(mainly anatase) remains the most used

catalyst as can be depicted fromTable 2 TiO2is reported to be

favored because of its nontoxic property cost efficiency andchemical and biological inertness Moreover TiO

2possesses

the most efficient photoactivity and the highest stability thusmaking it suitable for industrial use [61]

ZnO has been described to degrade lignin under visiblelight sources [48 62] whereas TiO

2is mostly applied in

connection to UV-light sources as highlighted in Table 2However both ZnO and TiO

2possess energy band gap

energy of 32 eV [23]Additives such as SiO

2[63] polyethylene oxide (PEO)

[24] and polyethylene glycol [64] have been added to TiO2

catalyst particularly when applying immobilized catalystAddamo et al [63] noted a high adhesion of TiO

2to glass

support material when precoating was done with SiO2

Moreover the precoating might have other advantages suchas a hindering diffusion of Na+ ions from the glass materialinto the nascent TiO

2film during heat treatment processes

Analogous to the addition of SiO2 polyethylene glycol

(PEG) has also been introduced to mitigate catalyst surfaceactivity modify surface hydrophobicity and also reduceagglomeration tendency of the TiO

2gel or TiO

2particles

in the suspensions [64] By a proper surface modificationinteraction between catalyst and substrate can be enhanced[55 63]

Kansal et al [48] varied catalyst (ZnO) dose from 05 gLto 20 gL for 01 gL kraft lignin solutions and found out thatthere was an optimum catalyst threshold value at 1 gL whichgives a catalyst to substrate ratio of 1 10

Dahm and Lucia [49] examined catalyst dose from 2 sdot10minus3 gL to 12sdot10minus2 gL for lignin solutions (fromwhite water

liner mill) of 4 sdot 10minus2 gL (catalyst to lignin ratio 5 sdot 10minus3ndash3 sdot 10minus2) at pH 8 and obtained best energy efficiency valuesand lignin degradation rates with a catalyst loading of 10 sdot10minus2 gLIn contrast Ma et al [56] applied far higher catalyst

concentration compared to Dahm and Lucia [49] Catalystconcentration was varied between 1 gL and 10 gL PtTiO

2

Best catalysis dose with respect to reaction turnover wasobtained at 5 gL PtTiO

2With the increase of catalyst dose at

pH 7 the reaction rate increased from 61 times 10minus3minminus1 (1 gLTiO2) to 71 sdot 10minus3minminus1 (5 gL TiO

2) and 99 sdot 10minus3minminus1

(10 gL TiO2)

Catalyst effect has been explained on the basis thatoptimum catalyst loading is dependent on the initial soluteconcentration An increase in catalyst dosage leads to a cor-responding increase of total active surface area for reactions

[65] To that at higher TiO2concentrations the photon flux is

more easily intercepted by the catalyst before penetrating intothe bulk of the system At the same time due to an increase inturbidity of the suspension with high dose of photocatalystthere is a decrease in penetration of UV light and hencephotoactivated volume of suspension or solution decreases[66]

In summary authors have obtained best catalyst to ligninrelations for different reaction designs and thus a generalrecommendation on catalyst dose is not possible Howeverwhen lignin solution is treated with increasing catalyst loadsa corresponding increase in degradation rate is observed untila threshold value is reached [48ndash50 56]

322 Influence of Metal Ion Addition (Doping) and AdditivesThe purpose of adding metal ion to photocatalyst is to miti-gate band gap energy through the introduction of intrabandgap states and as a consequence produce a bathochromicshift in the absorption spectrum [37] Altering the absorptionspectral range gives the possibility to exploit both the visiblelight spectrum and UV light sources Metal ion doping isalso introduced to serve as electron or hole traps in orderto minimize recombination between generated electron-holepairs [37]

Portjanskaja and Preis [50] studied the addition of Fe2+ions to an acidic lignin solution and found an increasein photocatalytic oxidation (PCO) efficiency The optimumFe2+ ions quantity was 28mgL while using 100mgL ligninsolution Upon further elevation of Fe2+ ions concentrationa corresponding reduction of the photocatalytic oxidationefficiency of lignin was noted Likewise Ohnishi et al [57]made a comparative study by doping platinum (Pt) silver(Ag) and gold (Au) ions to TiO

2 In these reactions 50mg of

catalyst (TiO2) was used with the addition of an equiva1ent

15 wt (based on TiO2) metal ion The addition of noble

metals brought about a faster decolorization of lignin Aushowed better results than Ag followed by Pt In the samecontext adding sodium hypochlorite as oxidant to PtTiO

2

catalyst an additional fivefold degradation rate was observedcompared to that without doping [56] Contradictory to theresults described above negligible effect of photocatalyticefficiency due to doping has been reported as well Awun-gacha Lekelefac et al [54] obtained little or no change indegradation rate by doping TiO

2-P25-SiO

2catalyst with Pt

ions (1 wt relative to TiO2catalyst) Likewise Portjanskaja

and Preis [50] noted a negligible change of photocatalyticefficiency of TiO

2when doped with nitrogen

Sarkanen et al [67] and Gellerstedt and Lindfors [68]reported the bias of peroxides to oxidation with reagentssuch as permanganate to favor aromatic moieties Oxidationagents like permanganate oxidizes predominantly aliphaticchains in alkaline and neutral media However by theapplication of H

2O2(Fenton system) lignin disappeared

completely [33] Tonucci et al [33] conclude that in orderto satisfactorily conserve the organic material the best com-promise appears to be the TiO

2photosystem which shows

low carbon consumption good preservation of the aromaticrings and greatly reduced mineralization


In summary different results have been obtained con-cerning the influence of noble metal ion addition Whilesome authors report an improvement in the photocatalyticefficiency upon their addition others report their addition ashaving no considerable influence However for reactions inwhich an improvement in the photocatalytic efficiency wasnoticed there was a threshold value to be considered Whenthe concentration of dopant surpasses this threshold valueelectron-hole recombination is favored and this has a negativeimpact to photocatalysis In such a case the space-chargelayer gets narrower and 119901-type dopants attract electrons andby virtue become negative They would now then act ashole acceptor attracting holes On the other hand 119899-typedopants which act as electron donor centers and possessexcess electrons attract holes as well [37]

323 Influence of Lignin Concentration Once the initiallignin concentration becomes higher exceeding a thresholdvalue an inhibitory effect on the photodegradationwas noted[47ndash49] This threshold value varies and depends on thereaction system and reaction parameters such as opticaldensity catalyst concentration and reaction volume Fromthe literature different authors have implemented varyinglignin concentrations probably to suit their reaction designFor example Ksibi et al [47] use 90mgL and AwungachaLekelefac et al [54] use 500mgL while Kansal et al [48]applied 10mgndash100mgL

Explanations arising from the findings are as followsat low lignin concentrations the incidental photonic fluxirradiated interacts with the catalyst generating radicals (eghydroxyl radicals (OH∙)) which allow a faster degradation[69] On the other hand high initial lignin concentrationsmay lead to tight adsorption which can suppress CO

2

evolution [51] and hence maintain chemical oxygen demand(COD) values Moreover low delignification yields maybe due to an inhibitory effect because of autoxidation bylow molecular weight lignin degradation products formed[24] Also due to the polymer structure of lignin which iscross-linked this makes it difficult for radical species acidand the aldehyde compounds produced to spread into theinner region of the substrate hence limiting autoxidationAs a worst case this might be the rate-determining step ofdelignification which is hindered [70ndash72]

In summary it can be concluded that the time taken forcomplete degradation depends on the initial concentration oflignin and faster degradation occurs at low lignin concentra-tions

324 Influence of pH Varying pH entails an alteration inthe properties of semiconductor-liquid interface [73] mainlyrelated to the acid-base equilibrium of the adsorbed hydroxylgroup [39] Furthermore pH also impacts lignin degradationrates [47 48 57] In this context several studies were carriedout with partly contradictory outcomes

Kansal et al [48] made pH investigations 3ndash11 undersolar light illumination using ZnO as catalyst Maximumdegradation was reached in alkaline conditions (pH 11)This is supported by Villasenor and Mansilla [74] reporting

an almost complete decolorization of kraft black liquorfrom pine wood at pH value of 116 in combination withZnO catalyst Similar results were achieved by Ohnishi etal [57] with TiO

2and ZnO being catalyst for bleaching

alkaline lignin in aqueous solution with TiO2and ZnO being

catalyst High activities at neutral pH were also reportedby Ohnishi et al [57] In contrast Ma et al [56] observedhigher reaction rates and rapid degradation of a syntheticlignin wastewater (prepared by dissolving commercial ligninpowder in aqueous solution pH 11) in acidic solution (pH 3)than in alkaline solutions at pH 11 for either TiO

2or PtTiO

2

catalystsReconsidering the photocatalytic principle the formed

superoxide anion radicals (∙O2

minus) are in a pH-dependentequilibriumwith perhydroxyl radicals (HO

2

∙) as follows [75]

HO2

∙999445999468 H+ + ∙O

2

minus pKa sim 48 (9)

See [76]∙O2

minus undergoes dismutation reaction resulting in H2O2

and O2competing to any other ∙O

2

minus triggered reaction Incase of low pH operation conditions in aqueous solutionsHO2

∙ becomes dominant whose reactivity is considerablyhigher compared to ∙O

2

minus [77] Subsequently HO2

∙ initiatessubstrate (S) oxidation to the radical cation (S+∙) and is itselfreduced to H

2O2[78] Thus increased degradation rates can

be reasonably expected supporting the results made by Ma etal [56] in an acidic environment ∙O

2

minus is extremely reactive inorganic solvents [77] Another aspect is the solubility of kraftlignin (soluble at pH gt 105) which reduces with decreasingpH whereas lignosulfonate should remain unaffected by pHin aqueous solution Moreover 120573ndashOndash4 bonds have beendescribed to be stable at acidic pH [11] In fact this couldadditionally explain the elevated degradation of kraft ligninmade by Kansal et al [48] and Villasenor and Mansilla [74]Nevertheless the contradictory results gained by Ma et al[56] still exist under the assumption that kraft ligninwas used(which would be supported by the high pH of 11 obviouslynecessary for dissolving the lignin powder) Although mostphotocatalytic reactions described in the literature are in anaqueous milieu lignin raw material and its fission productsmay however vary considerably Therefore the optimal pHis most likely to be reaction specific and has to be evaluatedexperimentally in principle

325 Influence of Illumination Many of the studies foundin the literature so far have not dealt on this subject per seWhat is found is the use of different illumination sourceseach having a specified power and lamp type However alltend to emitUV-light between the range 280ndash420 nm Table 2depicts this in detail Other illumination sources include thevisible light spectrum

In general terms illumination influences in that it ini-tiates photocatalysis by generating electron-hole pair in thesemiconductor particles [38 39] Dahm and Lucia [49]altered illumination intensity while observing lignin degra-dation In this study 004 gL lignin was used and lightintensity was varied 223ndash445mWcm3 It was found out thathigher illumination intensities correlated well with higher


initial degradation rates and hence total lignin degradation[49] Neppolian et al [69] report degradation to be propor-tional to radiation intensity and best results are achieved forlow lignin concentrations because of enhanced interactionbetween catalyst and incidental photonic flux

In summary high illumination power causes a corre-sponding high initial degradation rate at low lignin concen-trations becausemaximum light penetration into the reactionmedium is favored

33 Process Analytical Methods Various analytical tech-niques have been used to monitor lignin degradation Atthe beginning of this subchapter analytics revealing com-pounds formed from lignin degradation are treated Thisincludes for example gas chromatography (GC) and 1HNMR (nuclear magnetic resonance) This is then followed byresults qualitative analytic measurements such as ultraviolet-visible (UV-Vis) spectroscopy and dissolved carbon (DC)A list of authors analytical techniques applied and resultsachieved are outlined in Table 3

Portjanskaja and Preis [50] studied lignin degradationby measuring the removal of phenols through colorimetricmeasurements As a result of 24 h photocatalytic oxidationunder neutral media conditions 80 of free phenols wereremoved Gas chromatography (GC) result from Ksibi et al[47] attested vanillin vanillic acid palmitic acid biphenyland 345-trimethoxy benzaldehyde structures after the pho-tocatalysis of lignin from black liquor This is in accordancewith the findings of Tonucci et al [33] reporting the formationof vanillin hydroxyl methoxy-acetophenone coniferyl alco-hol coniferyl aldehyde methanol formic acid acetic acidand small amounts of C-2 and C-3 alcohols as degradationproducts1H NMR spectral analysis of lignin before illumination

and after 24 h of illumination showing characteristic bandsof aromatic rings methoxy and aliphatic side chains wascompared with each other Results revealed that the aro-matic ring degraded faster than the aliphatic chain [51]Fourier transformation infrared spectroscopy (FTIR) showedbands corresponding to CH

3 CH2 and CH which remained

unchanged after illumination while bands corresponding toaromatic rings disappeared as a result of illumination [51 53]

Results obtained from the combination of photochemicaland electrochemical oxidation [52 53] were similar to thoseof Tanaka et al [51] Here 13C-NMR confirmed the presenceof the carbonyl functionality and the presence of vanillinand vanillic acid after 12 h photochemical-electrochemicaloxidation These results showed that the combination of aphotocatalytic and an electrochemical oxidation significantlyenhanced the efficiency of lignin degradationThis is becausethe applied anodic potential bias greatly suppressed therecombination of photogenerated electrons and holes [53]

Ultraviolet spectrophotometry offers a convenientmethod to qualitatively and quantitatively analyze ligninin solution [79] This is reflected by the large number ofpublications using this technique [17 33 47ndash51 56 58 80]This is most likely due to its simplicity to interpret lignindegradation Lignins absorb UV light with high molar

200 220 240 260 280 300 320 340 360

00

05

10

15

20

25

Abso

rban

ce

Wavelength (nm)0min

30min

60min

120min

180min

300min

360min

420min

1200min

Figure 8 Time dependent UV-Vis absorption spectra of aqueouslignin solution from waste paper water irradiated with UV light(280ndash420 nm) for different time intervals The spectra are obtainedfor sol-gel derived TiO

2nanocrystalline coating (TiO

2-P25-SiO

2)

[54]

extinction coefficients because of the several methox-ylated phenylpropane units of which they are composed [33]Figure 8 depicts a series of photometric scans of ligninsul-fonate from paper waste water showing a gradual reductionof absorbance during photocatalytic treatment [54] Herethe absorption peaks are around 210 nm and 280 nmAbsorbance decreases with time implying the decompositionof lignin and the deterioration of chromophore groups [54]

Peaks at 210 nmcorrespond to portions of the unsaturatedchains while those at 280 nm correspond to unconjugatedphenolic hydroxyl groups [17] and the aromatic moiety [57]of the lignin molecule The absorption tailing to the longwavelength region arises from the color of lignin [57] Lignindegradation has been reported either at wavelength around280 nm corresponding to unconjugated phenolic hydroxylgroups [17 48 51 58] or for both wavelengths (210 nm and280 nm) [33 54 57] Kobayakawa et al [81] noted some otherabsorbance at wavelengths lower than 250 nm and pointedout that this could be due to the modification of ligninfragmentations leading to the formation of transient specieslikemethanol ethanol formaldehyde formic acid and oxalicacid among others

Analyticalmethods to effectively quantify lignin degrada-tion by calculating the oxygen demand by organic substancesand remaining organic carbon before and after photocatalysishave been studied Amongst the methods are dissolvedcarbon (DC) [49 51 58] chemical oxygen demand (COD)[47 48 50 57 80] biochemical oxygen demand (BOC) [50]dissolved organic carbon (DOC) [56] and American dyemanufacture institute value (ADMI) [56] COD and BODdescribe the oxygen demand by organic substances to be


Figure 9 Gradual change from the characteristic yellow ligninsulfonate to a colorless liquid after a period of 20 h Catalyst TiO

2-

P25 (Degussa) +TEOSUV-light 25∘C lignin concentration 05 gL[54]

converted to CO and CO2and H

2O and NH

3 Total organic

carbon (TOC) describes the amount of carbon bound inan organic compound while DOC describes the dissolvedfraction of organic carbon ADMI measures the amount ofdyestuff in water

Decolorization of lignin solution has been reported tobe another parameter observed during photocatalytic degra-dation Color is an indirect indicator of the lignin amountThe higher the color intensity of the solution is the greaterthe lignin content is (high concentrated lignin solutions egblack liquor appear dark brown) [82] Thus color changescan be interpreted as conversion of lignin to transient speciesor conversion to CO

2and H

2O Awungacha Lekelefac et al

[54] observed a gradual change from the characteristic yellowlignin (when highly diluted) to a colorless liquid after a periodof 20 h with sol-gel derived TiO

2nanocrystalline coatings on

sintered borosilicate glass as depicted in Figure 9 A corre-sponding decrease in DC values close to 82 was observedfor TiO

2-P25-SiO

2catalyst confirming degradation This is

shown in Figure 10These findings are analogous to that of Ohnishi et al

[57] who reported the bleaching of lignin when illuminatedcontinuously and that the solution becomes colorless Tothat the chemical oxygen demand (COD) value decreasesgenerating carbon dioxide and a small amount of carbonmonoxide as the main gaseous products COD removalwas reported to be effective at low lignin concentrations ascompared to high lignin concentrations [48]

Another applied analytical technique is fluorescencedetection directly coupled to a high performance liquidchromatography (HPLC) as a means to identify nonaliphaticcomponent in the complex mixture of lignin degradationproducts [54] Fluorescence emission in lignin is attributedto aromatic structures such as conjugated carbonyl biphenylphenylcoumarone and stilbene groups [83 84] AwungachaLekelefac et al [54] observed peaks on both HPLC and

0 200 400 600 800 1000 12000

50

100

150

200

250

Diss

olve

d ca

rbon

(ppm

)

t (min)

TiO2-P25-SiO2

TiO2-P25-SiO2 + PtTiOSO4minus30 6wt

ZnO + TiO2-P25-SiO2

No coating UV light

Figure 10 Variation of DC with time of aqueous lignin solutionfrom waste paper water irradiated with UV light (280ndash420 nm) fordifferent time intervals The spectra are obtained for sol-gel derivedTiO2nanocrystalline coatings (TiO

2-P25-SiO

2+Pt TiO

2-P25-SiO

2

TiOSO4minus306 wt ZnO + TiO

2-P25-SiO

2) [54]

fluorescence chromatograms suggesting the production ofnew substances and fluorophores

Despite developed analytical technologies analyzinglignin degradation products remains challenging Proofssuch as mass spectroscopy (MS) HPLC 13C or 1H-NMRspectra from photocatalytic lignin degradations are not yetestablished The setback to qualitatively and quantitativelyanalyze lignin and its degradation products starts from thenative lignin polymer itself with its indefinite polymericstructure and multiple bond types Also the influence ofdifferent pretreatments additives and the wide variety ofcompounds obtainable from its degradation makes ligninanalysis challenging [85] Moreover lignin streams couldcontain proteins inorganic salts and other potential poisonsthat generally complicate catalysis [4]

The challenge to identify and separate the productsstreams derived from the photocatalytic degradation ligninis also worth noting Lignin product stream is highly func-tionalized and conventional techniques such as gas chro-matography have the disadvantage of requiring a time-consuming derivatization step Also because of high boilingpoint of substances arising from lignin degradation it is noteasily applicable High performance liquid chromatography(HPLC) seems to be the remedy because analysis can becarried out without derivatization but the exact identificationof the separated substances is difficult because of the numer-ous peaks arising from such a chromatogram [87] Unfortu-nately well-established databases such as that of the nationalinstitute of standard and technology (NIST) [88] cannot giveinformation onHPLC-MS chromatogramsThis is because ofthe ionization sources such as electrospray ionization (ESI)


Table 4 Main advantages and disadvantages photocatalysis versus enzymatic biocatalysis

Lignin degradation process Advantages Disadvantages

Photocatalysis(single stage)

(i) Relatively fast degradation of complex as wellas nonbiodegradable organic (macro)molecules(ii) Stable catalysts(iii) Moderate reaction conditions

(i) Not selective(ii) Limited selection of operating conditions(iii) Energy costs

Enzymatic conversion(single stage)

(i) More selective(ii) Moderate reaction conditions

(i) High enzyme loads required otherwise ligninhydrolysis is quite slow [16](ii) Enzymes are less stable1(iii) cost-intensive (POXs)2

1For example POXs are sensitive to high H2O2 concentrations2According to Torres and Ayala [86]

and atmospheric pressure chemical ionization (APCI) forLC-MS while GC-MS is based on electron ionization Aremedy to this can be the development of a database ofmodel lignin compounds based on a unanimous HPLC-MSmeasuring procedure This would mean much time and costexpensive investments for adequate personnel and material

Though product identification based on peak superpo-sition gives information on a possible product this can-not always be true for lignin degradation because of thelarge number of possible degradation products In order toproperly identify products from lignin degradation productisolation techniques are to be implemented and further ana-lytic methods such as tandem mass spectroscopy (MSMS)and other advanced structure enhancing research techniquessuch as 1H-NMR 13C-NMR have to be studied extensively

4 Photocatalysis and Its Suitability asIntegrated Technology in MultistageConcepts with Biocatalysis

Depending on lignin treatment specification photocatalysiswill find application for complete lignin mineralization toCO2and H

2O (single stage) or as integrated technology in

a multistage system aiming at partial conversion of ligninmacromolecules to organic low molecular weight intermedi-ates for a consecutive biological oxidation finally generatingvalue added end-products [15]

For biological oxidation of lignin or lignin deriva-tives H

2O2-dependent ligninolytic heme peroxidases (POXs

including lignin peroxidase (LiP EC 111114) manganeseperoxidase (MnP EC 111113) versatile peroxidase (VPEC 111116) O

2-dependent laccases (Lac EC 11032) and

extracellular enzymes from Basidiomycetous white-rot fungiare the most efficient lignin degraders in nature [89] Thussuch enzymatic systems especially POXs (with high redoxpotentials) have attractedmuch interest as industrial biocata-lyst [86 90]The enzyme degradationmechanism (in nature)is facilitated by nonenzymatic processes mainly throughfree ∙OH radicals also generated by the fungus (Fenton-type reaction) Those ∙OH radicals enable the requiredphysical contact between the enzymes and structural units ofthe lignin molecule due to numerous nonspecific oxidative

reactions [91] Both the photocatalytic (equations (2)ndash(7))and the POX reactionmechanism recently reviewed by Busseat al [25] are quite similar Consequently a combination ofphotocatalysis followed by an enzymatic oxidation maybe apromising concept utilizing lignin derivatives for exampleoriginated from industrial effluents [15 92] The advantagesforming biobased products are as follows see also Table 4 inthis context A reduction of the lignin polymerization degreevia photocatalysis at best in more biodegradable interme-diates and a simultaneous detoxification causes savings inenzyme costs since it will be expected that less enzyme loadsare necessary for sufficiently rapid reaction rates [15 91] As aresult hydraulic retention times in bioreactor systems shouldbe diminished Moreover the delignification is expectedto be enhanced simultaneously which was in recent yearsshown in a dual system by Kamwilaisak and Wright [93]using TiO

2H2O2UV for photocatalytic pretreatment and

Lac (from Trametes versicolor) in the subsequent biocatalyticstep Within 24 h they obtained in their dual system anelevation in delignification of 20 (without H

2O2) up to at

least 50 when H2O2was present

In previous studies the treatment of lignin (from thepulp and paper industry) containing effluents by fungus asa biological system (excreting appropriate lignin degradingenzyme cocktails) were more focused for posttreatmentexclusively (Duran et al [92] Reyes et al [94] and Gonzalezet al [95]) Shende et al [17] even examined ligninolyticbacteria with photooxidized kraft lignin as substrate

Although POXs are potential industrial biocatalysts [86]no application studies were found for the direct use in suchdual systems as described above The major reason may bethe complexity of the reaction mechanism (inclusive ligninderivatives as substrate and their analysis) per se on the onehand slowing down research and development processes Onthe other hand POXs are sensitive to their cosubstrate H

2O2

once it is supplied in excess causing considerable inactivation(for details refer to Busse et al [25]) At the present severalstudies are carried out modifying these enzymes regardingenhanced stability activity and selectivity as well Henceit can be expected that their technological applicability willbe raised significantly right after successful modification isreached [86]


5 Concluding Remarks

It is widely assumed that the photocatalytic degradation oflignin follows a radical reaction pathway which is similar tothat considered in thermal electrochemical and biochemicalprocesses However reporting on the degradation pathway oflignin derivatives and even that of lignin model compoundsare still amajor challengeThis is probably due to the complexnature and variety of possible degradation products Indeedthemechanism is far more complex considering other factorssuch as type of lignin type of catalyst pH illuminationsource and additives

Generally comparing the different photochemical pro-cesses poses a big challenge because of the wide variablesinvolved These discrepancies start from the source and typeof lignin followed by differences in reactor design illumi-nation source intensity of radiation and different types ofcatalyst An ideawould be to have a specific reference reactionwith well-defined starting parameters which include lignintype source and purity catalyst specifications illuminationsource and intensity so as to ease comparison of results

Basic process parameters such as catalyst concentrationsubstrate concentration addition of metal ion to catalyst pHand illumination have been discussed

Despite developed analytical technologies analyzinglignin degradation products remains challenging Proofssuch as mass spectroscopy (MS) HPLC 13C or 1H-NMRspectra from photocatalytic lignin degradations are not yetestablished

In order to properly identify products from lignin degra-dation product isolation techniques are to be implementedand further analytic methods such as MSMS and otheradvanced structure enhancing research techniques such as1H-NMR and 13C-NMR have to be studied extensively Aremedy to this can be the development of a databank ofmodel lignin compounds based on a unanimous HPLC-MSmeasuring procedure This would mean much time and costexpensive investments for adequate personnel and material

Photocatalysis is denoted as the most popular ligninpretreatment technology besides ozonation [96] Photo-catalyzed lignin may be an appropriate substrate for aconsecutive biocatalytic process using ligninolytic enzymes(POX andor Lac) as supported by experimental results ofKamwilaisak and Wright [93] Combining the advantages ofboth catalytic processes savings in the overall process costswill be expected in addition to elevated lignin conversionNonetheless extensive research work including POX modi-fications is still required

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Authorsrsquo Contribution

Colin Awungacha Lekelefac and Nadine Busse contributedequally to this work

Acknowledgments

The authors gratefully thank the Federal Ministry of Educa-tion and Research (BMBF) for funding (FKZ17N0310) Theresearchers also thank the Hessen State Ministry of HigherEducation Research andArts for the financial support withinthe Hessen initiative for scientific and economic excellence(LOEWE)

References

[1] Crude Oil and Commodity Prices httpwwwoil-pricenet[2] Research Directorate-General for World Energy Technology

and Climate Policy Outlook (WETO) Luxembourg Office forOfficial Publications of the European Communities 2003

[3] Green and Natural Polymers Are on the Rise 2014 httpwwwpolymersolutionscombloggreen-and-natural-polymers-on-the-rise

[4] J Zakzeski P C Bruijnincx A L Jongerius and B M Weck-huysen ldquoThe catalytic valorization of lignin for the productionof renewable chemicalsrdquo Chemical Reviews vol 110 no 6 pp3552ndash3599 2010

[5] B KammM Kamm P R Gruber and S KromusBiorefineries-Industrial Processes and Products Status Quo and Future Direc-tions vol 1 Wiley-VCH 2006

[6] R L Howard E Abotsi E L J van Rensburg and S HowardldquoLignocellulose biotechnology issues of bioconversion andenzyme productionrdquoAfrican Journal of Biotechnology vol 2 no12 pp 602ndash619 2003

[7] M Stocker ldquoBio- und BTL-Kraftstoffe in der Bioraffineriekatalytische Umwandlung Lignocellulose-reicher Biomasse mitporosen Stoffenrdquo Angewandte Chemie vol 120 no 48 pp9340ndash9351 2008

[8] J-P Lange ldquoLignocellulose conversion an introduction tochemistry process and economicsrdquo Biofuels Bioproducts andBiorefining vol 1 no 1 pp 39ndash48 2007

[9] D A I Goring ldquoThe physical chemistry of ligninrdquo Pure andApplied Chemistry vol 5 no 1-2 pp 233ndash310 1962

[10] M Ek G Gellerstedt and G HenrikssonWood Chemistry andBiotechnology Pulp and Paper Chemistry and Technology vol 1Walter de Gruyter GmbH amp Co KG Berlin Germany 2009

[11] B Saake and R Lehnen ldquoLigninrdquo in Ullmannrsquos Encyclopedia ofIndustrial Chemistry Wiley-VCH Verlag GmbH amp Co KGaAWeinheim Germany 2012

[12] M N S Kumar A K Mohanty L Erickson and M MisraldquoLignin and its applications with polymersrdquo Journal of BiobasedMaterials and Bioenergy vol 3 no 1 pp 1ndash24 2009

[13] R J A Gosselink E de Jong B Guran and A AbacherlildquoCo-ordination network for ligninmdashstandardisation produc-tion and applications adapted to market requirements(EUROLIGNIN)rdquo Industrial Crops and Products vol 20 no 2pp 121ndash129 2004

[14] D Fengel and G Wegener Wood Chemistry UltrastructureReactions Verlag Kessel 1984

[15] D Mantzavinos and E Psillakis ldquoEnhancement of biodegrad-ability of industrial wastewaters by chemical oxidation pre-treatmentrdquo Journal of Chemical Technology and Biotechnologyvol 79 no 5 pp 431ndash454 2004


[16] M Dashtban H Schraft and W Qin ldquoFungal bioconversionof lignocellulosic residues Opportunities amp perspectivesrdquo Inter-national Journal of Biological Sciences vol 5 no 6 pp 578ndash5952009

[17] A Shende R Jaswal D Harder-Heinz A Menan and RShende ldquoIntergrated photocatalytic and microbial degradationof kraft ligninrdquo Cleantech pp 120ndash123 2012

[18] F S Chakar and A J Ragauskas ldquoReview of current and futuresoftwood kraft lignin process chemistryrdquo Industrial Crops andProducts vol 20 no 2 pp 131ndash141 2004

[19] W G Glasser and H R Glasser ldquoEvaluation of ligninrsquoschemical structure by experimental and computer simulationtechniquesrdquo Paperi ja Puu vol 63 pp 71ndash83 1981

[20] M Erickson S Larsson and G E Miksche ldquoZur Struktur desLignins der FichterdquoActaChemica Scandinavica vol 27 pp 903ndash914 1973

[21] H Nimz ldquoDas Lignin der BuchemdashEntwurf eines Konstitution-sschemasrdquo Angewandte ChemiemdashInternational Edition vol 86pp 336ndash344 1974

[22] D V Evtuguin C P Neto J Rocha and J D P de JesusldquoOxidative delignification in the presence of molybdovana-dophosphate heteropolyanions mechanism and kinetic stud-iesrdquo Applied Catalysis A General vol 167 no 1 pp 123ndash1391998

[23] A L Linsebigler G Lu and J T Yates Jr ldquoPhotocatalysis onTiO2surfaces Principles mechanisms and selected resultsrdquo

Chemical Reviews vol 95 no 3 pp 735ndash758 1995[24] Y Miyata K Miyazaki M Miura Y Shimotori M Aoyama

and H Nakatani ldquoSolventless delignification of wood flourwith TiO

2poly(ethylene oxide) photocatalyst systemrdquo Journal

of Polymers and the Environment vol 21 no 1 pp 115ndash121 2013[25] N Busse D Wagner M Kraume and P Czermak ldquoReaction

kinetics of versatile peroxidase for the degradation of lignincompoundsrdquoTheAmerican Journal of Biochemistry andBiotech-nology vol 9 no 4 pp 365ndash394 2013

[26] M Tien and T K Kirk ldquoLignin-degrading enzyme fromphanerochaete chrysosporium Purification characterizationand catalytic properties of a uniqueH

2O2-requiring oxygenaserdquo

Proceedings of the National Academy of Sciences vol 81 pp2280ndash2284 1984

[27] T K Kirk M Tien P J Kersten M D Mozuch and BKalyanaraman ldquoLigninase of Phanerochaete chrysosporiumMechanism of its degradation of the non-phenolic arylglycerol120573-aryl ether substructure of ligninrdquo Biochemical Journal vol236 no 1 pp 279ndash287 1986

[28] T Lundell RWever R Floris et al ldquoLignin peroxidase L3 fromPhlebia radiata pre-steady-state and steady-state studies withveratryl alcohol and a non-phenolic lignin model compound1-(34-dimethoxyphenyl)-2-(2-methoxyphenoxy)propane-13-diolrdquo European Journal of Biochemistry vol 211 no 3 pp391ndash402 1993

[29] H E Schoemaker T K Lundell A I Hatakka and K PiontekldquoThe oxidation of veratryl alcohol dimeric lignin models andlignin by lignin peroxidase the redox cycle revisitedrdquo FEMSMicrobiology Reviews vol 13 no 2-3 pp 321ndash331 1994

[30] J M Palmer P J Harvey and H E Schoemaker ldquoThe role ofperoxidases radical cations and oxygen in the degradation oflignin [and discussion]rdquo Philosophical Transactions of the RoyalSociety of London A vol 321 no 1561 pp 495ndash505 1987

[31] C Hill Wood Modification Chemical Thermal and OtherProcesses John Wiley amp Sons Chichester UK 2006

[32] Y-H Xu H-R Chen Z-X Zeng and B Lei ldquoInvestigation onmechanism of photocatalytic activity enhancement of nanome-ter cerium-doped titaniardquo Applied Surface Science vol 252 no24 pp 8565ndash8570 2006

[33] L Tonucci F Coccia M Bressan and N DrsquoAlessandro ldquoMildphotocatalysed and catalysed green oxidation of lignin auseful pathway to low-molecular-weight derivativesrdquoWaste andBiomass Valorization vol 3 no 2 pp 165ndash174 2012

[34] A Castellan N Colombo C Vanucci P Fornier de HViolet and H Bouas-Laurent ldquoPhotodegradation of ligninA photochemical study of an O-methylated 120572-carbonyl 120573-1lignin model dimer 12-di(3101584041015840-dimethoxyphenyl) ethanone(deoxyveratroin)rdquo Journal of Photochemistry and PhotobiologyA vol 51 pp 451ndash467 1990

[35] A Fujishima X Zhang and D A Tryk ldquoTiO2photocatalysis

and related surface phenomenardquo Surface Science Reports vol63 no 12 pp 515ndash582 2008

[36] C S Turchi and D F Ollis ldquoPhotocatalytic reactor designan example of mass-transfer limitations with an immobilizedcatalystrdquo The Journal of Physical Chemistry vol 92 no 23 pp6852ndash6853 1988

[37] R Subasri M Tripathi K Murugan J Revathi G V N Raoand T N Rao ldquoInvestigations on the photocatalytic activity ofsolndashgel derived plain and Fe3+Nb5+ doped titania coatings onglass substratesrdquo Materials Chemistry and Physics vol 124 pp63ndash68 2010

[38] N Serpone ldquoRelative photonic efficiencies and quantum yieldsin heterogeneous photocatalysisrdquo Journal of Photochemistry andPhotobiology A Chemistry vol 104 no 1ndash3 pp 1ndash12 1997

[39] M R Hoffmann S T Martin W Choi and D W BahnemannldquoEnvironmental applications of semiconductor photocatalysisrdquoChemical Reviews vol 95 no 1 pp 69ndash96 1995

[40] C D Jaeger and A J Bard ldquoSpin trapping and electron spinresonance detection of radical intermediates in the photode-composition of water at titanium dioxide particulate systemsrdquoThe Journal of Physical Chemistry vol 83 no 24 pp 3146ndash31521979

[41] R W Matthews ldquoHydroxylation reactions induced by near-ultraviolet photolysis of aqueous titaniumdioxide suspensionsrdquoJournal of the Chemical Society Faraday Transactions vol 80no 2 pp 457ndash471 1984

[42] A E H Machado A M Furuyama S Z Falone R RuggieroD D S Perez and A Castellan ldquoPhotocatalytic degradation oflignin and lignin models using titanium dioxide the role of thehydroxyl radicalrdquoChemosphere vol 40 no 1 pp 115ndash124 2000

[43] W Sigg and L Stumm Aquatische Chemie Stuttgart 2 AuflageBG Teubner Stuttgart Germany 1991

[44] O Legrini E Oliveros and A M Braun ldquoPhotochemicalprocesses for water treatmentrdquo Chemical Reviews vol 93 no2 pp 671ndash698 1993

[45] G Rothenberger J Moser M Gratzel N Serpone and DSharma ldquoCharge carrier trapping and recombination dynamicsin small semiconductor particlesrdquo Journal of the AmericanChemical Society vol 107 no 26 pp 8054ndash8059 1985

[46] P Mazellier M Sarakha A Rossi and M Bolte ldquoThe aqueousphotochemistry of 26-dimethylphenol Evidence for the frag-mentation of the 120572 C-C bondrdquo Journal of Photochemistry andPhotobiology A vol 115 no 2 pp 117ndash121 1998

[47] M Ksibi S B Amor S Cherif E Elaloui A Houas and MElaloui ldquoPhotodegradation of lignin from black liquor using aUVTiO

2systemrdquo Journal of Photochemistry and Photobiology

A vol 154 no 2-3 pp 211ndash218 2003


[48] S K Kansal M Singh and D Sud ldquoStudies on TiO2ZnO

photocatalysed degradation of ligninrdquo Journal of HazardousMaterials vol 153 no 1-2 pp 412ndash417 2008

[49] A Dahm and L A Lucia ldquoTitanium dioxide catalyzed pho-todegradation of lignin in industrial effluentsrdquo Industrial andEngineering Chemistry Research vol 43 no 25 pp 7996ndash80002004

[50] E Portjanskaja and S Preis ldquoAqueous photocatalytic oxidationof lignin the influence of mineral admixturesrdquo InternationalJournal of Photoenergy vol 2007Article ID76730 7 pages 2007

[51] K Tanaka R C R Calanag and T Hisanaga ldquoPhotocatalyzeddegradation of lignin on TiO

2rdquo Journal of Molecular Catalysis

A Chemical vol 138 no 2-3 pp 287ndash294 1999[52] M Tian J Wen D MacDonald R M Asmussen and A Chen

ldquoA novel approach for lignin modification and degradationrdquoElectrochemistry Communications vol 12 no 4 pp 527ndash5302010

[53] K PanM Tian Z-H Jiang B Kjartanson and A Chen ldquoElec-trochemical oxidation of lignin at lead dioxide nanoparticlesphotoelectrodeposited on TiO

2nanotube arraysrdquo Electrochim-

ica Acta vol 60 pp 147ndash153 2012[54] C Awungacha Lekelefac J Hild P Czermak and M Herren-

bauer ldquoPhotocatalytic active coatings for lignin degradationin a continuous packed bed reactorrdquo International Journal ofPhotoenergy vol 2014 Article ID 502326 10 pages 2014

[55] C Awungacha Lekelefac P Czermak and M HerrenbauerldquoEvaluation of photocatalytic active coatings on sintered glasstubes by methylene bluerdquo International Journal of Photoenergyvol 2013 Article ID 614567 9 pages 2013

[56] Y-S Ma C-N Chang Y-P Chiang H-F Sung and A CChao ldquoPhotocatalytic degradation of lignin using PtTiO

2as

the catalystrdquo Chemosphere vol 71 no 5 pp 998ndash1004 2008[57] H Ohnishi M Matsumura H Tsubomura and M Iwasaki

ldquoBleaching of lignin solution by a photocatalyzed reactionon semiconductor photocatalystsrdquo Industrial and EngineeringChemistry Research vol 28 no 6 pp 719ndash724 1989

[58] C A K Gouvea F Wypych S G Moraes N Duran and PPeralta-Zamora ldquoSemiconductor-assisted photodegradation oflignin dye and kraft effluent by Ag-doped ZnOrdquo Chemospherevol 40 no 4 pp 427ndash432 2000

[59] A V Vahatalo K Salonen M Salkinoja-Salonen and AHatakka ldquoPhotochemical mineralization of synthetic lignin inlake water indicates enhanced turnover of aromatic organicmatter under solar radiationrdquo Biodegradation vol 10 no 6 pp415ndash420 1999

[60] H de Lasa B Serrano and M Salaices Photocatalytic ReactionEngineering Springer New York NY USA 2005

[61] K Hashimoto H Irie and A Fujishima ldquoTiO 2 photocatalysisA historical overview and future prospectsrdquo Japanese Journal ofApplied Physics vol 44 no 12 pp 8269ndash8285 2005

[62] M A Behnajady N Modirshahla and R Hamzavi ldquoKineticstudy on photocatalytic degradation of CI Acid Yellow 23 byZnOphotocatalystrdquo Journal ofHazardousMaterials vol 133 no1ndash3 pp 226ndash232 2006

[63] M Addamo V Augugliaro A di Paola et al ldquoPhotocatalyticthin films of TiO

2formed by a sol-gel process using titanium

tetraisopropoxide as the precursorrdquo Thin Solid Films vol 516no 12 pp 3802ndash3807 2008

[64] N Negishi K Takeuchi and T Ibusuki ldquoPreparation of theTiO2thin filmphotocatalyst by the dip-coating processrdquo Journal

of Sol-Gel Science and Technology vol 13 no 1ndash3 pp 691ndash6941998

[65] L Rideh A Wehrer D Ronze and A Zoulalian ldquoPhotocat-alytic degradation of 2-chlorophenol in TiO

2aqueous suspen-

sion modeling of reaction raterdquo Industrial and EngineeringChemistry Research vol 36 no 11 pp 4712ndash4718 1997

[66] R-ADoongC-HChen RAMaithreepala and S-MChangldquoThe influence of pHand cadmiumsulfide on the photocatalyticdegradation of 2-chlorophenol in titanium dioxide suspen-sionsrdquoWater Research vol 35 no 12 pp 2873ndash2880 2001

[67] K V Sarkanen A Islam and C D Anderson ldquoOzonationrdquo inMethods in Lignin Chemistry S Y Lin and C W Dence EdsSpringer Series inWood Science pp 387ndash406 Springer BerlinGermany 1992

[68] G Gellerstedt and E-L Lindfors ldquoStructural changes in ligninduring kraft pulpingrdquo Holzforschung vol 38 no 3 pp 151ndash1581984

[69] B Neppolian H C Choi M V Shankar B Arabindoo andV Murugesan in Proceedings of the International Symposiumon Environmental Pollution Control and Waste Management(EPCOWM 02) p 647 2002

[70] C Pouteau P Dole B Cathala L Averous and N BoquillonldquoAntioxidant properties of lignin in polypropylenerdquo PolymerDegradation and Stability vol 81 no 1 pp 9ndash18 2003

[71] J Hafren T Fujino and T Itoh ldquoChanges in cell wall archi-tecture of differentiating tracheids of Pinus thunbergii duringlignificationrdquo Plant and Cell Physiology vol 40 no 5 pp 532ndash541 1999

[72] T Dizhbite G Telysheva V Jurkjane and U Viesturs ldquoChar-acterization of the radical scavenging activity of lignins naturalantioxidantsrdquo Bioresource Technology vol 95 no 3 pp 309ndash3172004

[73] K Hofstadler R Bauer S Novalic and S G Heisier ldquoNew reac-tor design for photocatalytic wastewater treatment with TiO

2

immobilized on fused-silica glass fibers photomineralization of4-chlorophenolrdquo Environmental Science amp Technology vol 28no 4 pp 670ndash674 1994

[74] J Villasenor and H D Mansilla ldquoEffect of temperature onkraft black liquor degradation by ZnO-photoassisted catalysisrdquoJournal of Photochemistry and Photobiology A Chemistry vol93 no 2-3 pp 205ndash209 1996

[75] B H Bielski D E Cabelli L A Ravindra and A B RossldquoReactivity of HO

2Ominus2Radicals in aqueous solutionrdquo Journal

of Physical Chemistry vol 14 pp 1041ndash1100 1985[76] B H J Bielski and A O Allen ldquoMechanism of the dispropor-

tionation of superoxide radicalsrdquo Journal of Physical Chemistryvol 81 no 11 pp 1048ndash1050 1977

[77] B Halliwell and J M C Gutteridge ldquoThe importance of freeradicals and catalytic metal ions in human diseasesrdquoMolecularAspects of Medicine vol 8 no 2 pp 89ndash193 1985

[78] J M Palmer P J Harvey and H E Schoemaker ldquoThe role ofperoxidases radical cations and oxygen in the degradation oflignin [and discussion]rdquo Philosophical Transaction of the RoyalSociety A vol 321 no 1561 pp 495ndash505 1987

[79] S Y Yin and C W Dense Methods in Lignin ChemistrySpringer New York NY USA 1992

[80] P Kumar S Kumar and N K Bhardwaj ldquoPhotocatalyticoxidation of elemental chlorine free bleaching effluent withUVTiO

2rdquo in Proceedings of the 2nd International Conference on

Environmental Science and Technology (ICEST rsquo11) SingaporeFebruary 2011

[81] K Kobayakawa Y Sato S Nakamura and A FujishimaldquoPhotodecomposition of Kraft lignin catalyzed by titanium


dioxiderdquo Bulletin of the Chemical Society of Japan vol 62 no11 pp 3433ndash3436 1989

[82] R B Kinstre ldquoAn overview of strategies for reducing theenvironmental impact of bleach-plant effluentsrdquo Tappi Journalvol 76 no 5 pp 105ndash113 1993

[83] A Castellan H Choudhury R Stephen Davidson and SGrelier ldquoComparative study of stone-ground wood pulp andnative wood 3 Application of fluorescence spectroscopy to astudy of the weathering of stone-ground pulp and native woodrdquoJournal of Photochemistry and Photobiology A Chemistry vol81 no 2 pp 123ndash130 1994

[84] B Albinsson S Li K Lundquist and R Stomberg ldquoThe originof lignin fluorescencerdquo Journal of Molecular Structure vol 508no 1ndash3 pp 19ndash27 1999

[85] S Baumberger A Abaecherli M Fasching et al ldquoMolar massdetermination of lignins by size-exclusion chromatographytowards standardisation of the methodrdquo Holzforschung vol 61no 4 pp 459ndash468 2007

[86] E Torres andM Ayala Biocatalysis Based on Heme PeroxidasesSpringer New York NY USA 1st edition 2010

[87] R Pecina P Burtscher G Bonn and O Bobleter ldquoGC-MSand HPLC analyses of lignin degradation products in biomasshydrolyzatesrdquo Fresenius Zeitschrift fur Analytische Chemie vol325 no 5 pp 461ndash465 1986

[88] NIST NIST Standard Reference Database The National Insti-tute of Standards and Technology 2014 httpwwwnistgovsrdnist1acfm

[89] T K Kirk and R L Farrell ldquoEnzymatic ldquocombustionrdquo themicrobial degradation of ligninrdquo Annual Review of Microbiol-ogy vol 41 pp 465ndash501 1987

[90] A TMartinez ldquoHigh redox potential peroxidasesrdquo in IndustrialEnzymes Structure Function and Applications K-B BeckerEd pp 477ndash488 Springer Amsterdam The Netherlands 1stedition 2007

[91] M Dashtban H Schraft T A Syed and W Qin ldquoFungalbiodegradation and enzymatic modification of ligninrdquo Interna-tional Journal of Biochemistry and Molecular Biology vol 1 no1 pp 36ndash50 2010

[92] N Duran E Esposito L H Innocentini-Mei and V P CanhosldquoA new alternative process for Kraft E1 effluent treatmentrdquoBiodegradation vol 5 no 1 pp 13ndash19 1994

[93] K Kamwilaisak and P C Wright ldquoInvestigating laccase andtitanium dioxide for lignin degradationrdquo Energy and Fuels vol26 no 4 pp 2400ndash2406 2012

[94] J Reyes M Dezotti H Mansilla J Villasenor E Espositoand N Duran ldquoBiomass photochemistry-XXII combined pho-tochemical and biological process for treatment of Kraft E1effluentrdquoApplied Catalysis B Environmental vol 15 no 3-4 pp211ndash219 1998

[95] L F Gonzalez V Sarria and O F Sanchez ldquoDegradationof chlorophenols by sequential biological-advanced oxidativeprocess using Trametespubescens and TiO

2UVrdquo Bioresource

Technology vol 101 no 10 pp 3493ndash3499 2010[96] J H Lora and W G Glasser ldquoRecent industrial applications

of lignin a sustainable alternative to nonrenewable materialsrdquoJournal of Polymers and the Environment vol 10 no 1-2 pp 39ndash48 2002

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy


Carbohydrate Chemistry

International Journal of


Journal of

Chemistry


Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of


Chromatography Research International


Applied ChemistryJournal of



Theoretical ChemistryJournal of


Journal of

Spectroscopy

Analytical ChemistryInternational Journal of


Journal of


Quantum Chemistry


Organic Chemistry International

ElectrochemistryInternational Journal of



CatalystsJournal of


Cellulosehemicellulose

lignin

Biomass

Pretreatment

Pyrolysis andgasification

Platformchemicals

Step 1

1

2

3

Step 2catalysis

Catalysis

Syngas

Furtherprocessing

catalysis

New technology

New technology

Current technology

Lignin

Cellulose

Hemicellulose

Fuelsbulk and fine

chemicals

PhenolBenzene Toluene Xylene

ProteinsLipidsAsh

SoilSaltsWater

KraftSulfiteOrganosolvPyrolysisSteamExplosionAFEXHot waterOther

For example Fischer-Tropsch methanol synthesis

COH2

OH

OH

OH

OH

OH

R R

ROH

OH

OH

OH

OH

OH

OH

O

OOO

HO

HO

O O

O

Figure 1 Lignocellulosic biorefinery scheme with particular emphasis on the lignin stream reprinted with permission from Zakzeski et al[4] copyright (2010) American Chemical Society

Figure 1 depicts an exemplary lignocellulosic biorefineryscheme with emphasis on the lignin stream For separa-tion purposes several pretreatment procedures are currentlyapplied in order to generate lignin derivatives (modificationin lignin structure) which can be differentiated on thebasis of their isolation method and their origin since theirphysical and chemical properties differ [9ndash11] The mostindustrialtechnical lignins (gt70 million tons per year) areobtained as waste material by the pulp and paper industry[12] mainly from the kraft process as noted by Kamm etal [5] 98 is burnt for energy recovery in the paper mills[13] while less than 2 is sold primarily in formulationof dispersants adhesives and surfactants [14] Lignin is anaromatic biopolymer of high potential fission products fora wide range of sectors and it is thus gaining attention forexample for the production of platform chemicals (Figure 1)Nonetheless lignin is still underutilized and fundamentalresearch and development are needed [5]This is explained byligninrsquos complex nature its recalcitrance to degradation andthe difficulty to analyze its numerous degradation productsTherefore intensive research goes on both sides processengineering and development (homogeneous heterogeneouscatalysis thermal electrochemical andor hybrid proce-dures) and process analytics

Photocatalysis is an advanced oxidation process (AOPs)[15] with the potential to transform lignin to value addedproducts such as phenol benzene toluene and xylene [4]In this context it can be applicable as stand-alone unit or it

can be coupledwith otherAOPs (eg Fentonrsquos reagent ozoneelectrochemical oxidation) as well as biocatalysis [15] (eghydrolysis through ligninolytic enzymes)

This paper is aimed at reviewing photocatalysis of indus-trial lignins in connection with evaluating the effects ofbasic operating parameters such as catalyst loading illu-mination intensity integration of metal ions and otheradditives pH and initial lignin concentration Furthermoreanalytical techniques used by different researchers are dis-cussed Finally a brief overview concerning the suitabilityof photocatalysis as a pretreatment method for subsequentbiocatalysis by ligninolytic systems for example fungal hemeperoxidases andor laccases is highlighted

2 Lignin as Raw MaterialChemical Structure and Sources

Lignin is the only naturally synthesized aromatic biopolymer[16] and after cellulose themost abundant renewable carbonsource on earth [17] In addition native lignin is a poly-disperse 3D macromolecule with an undefined molecularmass The biopolymer is made up of randomly arrangedphenylpropane units 119901-coumaryl alcohol coniferyl alcoholand sinapyl alcohol as depicted in Figure 2 contributing to anirregular structure [11]

An overview of the common interunit linkages and itsestimated proportions are shown in Table 1 For a better


1

2

3

45

120572120573

120574OH

OH

p-Coumaryl alcohol

OCH3

OH

OH


OCH3H3CO

OH

OH














2(h+VB)



2 respectively



Spirodienone

O

OO

O

O

OHO

OO

O

O

O

O

OHO

O

O

O

O

O

O

OO O

O

O

O

O

O

O

O

OH

OO

OO

O

O

OO




HO

OAr

HO

OH

OHOH

OH

HO

HO

OH

HO

OH

HO

OH

HO

OH

HO

OH

HO

OH

HO

OH

HO

OH

HO4-O-5

OH

HOOH

120573-120573

5-5998400

120573-O-4

120573-1

120573-1

O


O2∙minus + H+ HO2

∙

2HO2∙

HO∙ + OHminus

∙OH


S∙+ + O2SO2

∙+

O2∙minus

∙O2minus



O2 + eminus

H2O2 + O2

H2O2 + eminus


h+ + OHminus

Electron capture

Recombination

eminus

h+

Conduction band

Valence band

Electron release

eminus

O2

(super oxide)

Light

OHminus




2O producing




TiO2


2(

eminusCBh+VB) (1)

TiO2(h+) +H

2O 997888rarr TiO

2+HO∙ +H+ (2)



MeO MeOMeOMeO

∙OO

O

O ∙

OH

HO+ +


RH

bond cleavage

Vanillin

O

OO

O

OO O

O

O

O

O

O

HO HO

HOHO

HO

HO

HO HO

OH OH

HO

OCH3

OCH3

OCH3

OCH3

OCH3 OCH3

OCH3

OCH3 OCH3

OCH3

h minusH∙OH∙∙

O2TiO2

HminusOH∙

C120572-C120573

∙



2

∙+ (4)


2+∙S+ (5)

TiO2(eminus) +O

2997888rarr TiO

2+∙O2

minus (6)

HO∙ + ∙O2

minus


(7)

TiO2(eminus) + TiO

2(h+) 997888rarr heat (8)









Adlerol


Enzyme1

23

4

4

1

2

3

5

5

6

6

Guaiacol

Veratraldehyde

Ketone

O

OO

O

O O

O

O

O

HO

HOHO

HO

OCH3

OCH3

OCH3

OCH3

OCH3

OCH3

120572120573

120574

minusH+

∙+

∙

∙+


O2

120572 120573

120574

HOHOHO

OCH3

OCH3OCH3

OCH3 OCH3

OCH3

OCH3

120572120572

120573 120573

120573

120574 120574

HO

HO

120574

OCH3

120573

HO

HO

120574

HO

OCH3

OCH3

OCH3

120572120573

120574







rutile TiO2[49] TiO


a few


Table2Summaryof

startingcond

ition

sfor

thep

hotocatalytic

degradationof

lignin

Reference

Lign

insource

Catalyst

Reactio

ncond

ition

s

MacHadoetal[42]

Peroxyform

icacid

lignins

from

eucalyptus

grandisw

ood(EL1)

EL1+

sodium

borohydride

TiO

2andH

2O2

Lign

inconcentration

025

mgmL119879=25∘C

pH11U

VVisradiatio

n120582gt300nm

40

0Wmercury

lampcylin

dricalPy

rexglassreactorcon

stanto

xygenbu

bblin

g

Ksibietal[47]

Water

solubleligninob

tained

from

blackliq

uor

TiO

2-P2

5(D

egussa)

Lign

inconcentration

90mgL119879=20∘C


pyrex

reactoro

pento

airPh

ilips

HPK

125W

lamp

Kansaletal[48]

Lign

infro

mwheatstr

awkraft

digestion

TiO

2-P2

5(D

egussa)a

ndZn

O

Lign

inconcentration

10ndash100

mgLin

100m

LZn

Ocatalystdo

se(05ndash20gL)pH

ofthes


mination

oxidantcon

centratio

n306times10minus6M


slurrypo


hypo

chlorite

solutio

n(4availableC

l 2)

Dahm

andLu

cia[

49]

Whitewater

from

indu

strialprocess

water

thatexits

inpaperm

achines

FischerS

cientifi

crutile

TiO

2

Lign

inconcentration

40mgLin

500m


42∘C

Rayonet

photochemicalcham

ber16

VWR8-W

blacklightpho

spho

r(350-nm

)lam

ps

constant

oxygen

bubb

lingpo

wer

ofillum

ination

128to

64Wlight

intensity

223ndash44

5mWcm

3

Portjanskajaand

Preis[50]

Lign

inpurchased

from

Aldric

hTiO

2P2

5-N(D

egussa)

Lign

inconcentration

100m

gLpH


open

toair

PhillipsT


inescent

mercury

UV-lampUV-radiation

120582gt360nm

pow

erdensity

ofirr

adiatio

n=07m

Wcm

2 visib

lelight

source

Tanaka

etal[51]

Lign

infro

mconiferous

woo

dTiO

2(TiO

2mdashTP

-2of

Fujititan)

Lign

inconcentration

0003to

003U


cylindrical

reactio

nvessel

Tonu

ccietal[33]

Ca2+andNH4

+ligninderiv

atives

TiO

2as

Degussa

P25

+po

lyoxom

etalates

(POM)H

2O2

Openqu

artztubes(20

mL)


1atm

multirayso

ften

UVlamps

of15W

power

eachU


Miyatae

tal[24]

Piceag

lehn

iiwoo

dflo

urTiO

2po

lyethylene

oxide(PE

O)

Reactorop

enpetrid

ish119879=30∘C119905=48h40

0Wmercury

lamp

Shende

etal[17]

Kraft

lignin

TiO

2-Zn

O-ZrO

2Lign

inconcentration

1mgmLin

10mL250W

Xeno

nlampandAM

15Glamp

filterpo

wer

density

ofirr

adiatio

n100m

Wcm

2 solarlam

psim

ulator

Tian

etal[52]

andPanetal[53]

Kraft

ligninfro

mblackliq

uor

Ta2O

5-IrO

2andPb

O2thin

film

TiO

2nano

tubePbO

2

Lign

inconcentration

30(w


119905=10minpow

erdensity

ofirr

adiatio

n20

mWcm

2 blue

waveT

M50

ASUVspot

lampEG

ampG2273

potentiosta

tgalvano


2NTPb

O2ele

ctrode

asworking

electrode

andPt

coilas

outere

lectrode

andAgAgC

lasreference

electrode

Awun

gachaL

ekele

fac

etal[54][55]

Lign

insulfo

natefro

mpaperw

aste

water

TiO

2as

Degussa

P25

TiO

2fro

msol-g

elprocesso

fTiOSO

4TT

IP

Lign

inconcentration

500m

gLin

200m

LOsram

Planon

light

sourceirradiance

30ndash4

0Wm


20nm

119905=20hreactoro

pento

air

recirculationsyste

mflow

rate225mLmin



dsand

results

from

different

workgrou

ps

Reference

Parameter

studied

Analytic

sRe

sult

MacHado

etal[42]

Roleof

hydroxylradicals

irradiatio

nof

ligninin

the

absencea

ndpresence

ofph

otocatalystT

iO2andH

2O2

Ultraviolet-v


scop

yionizatio

nabsorptio

nspectro

scop

y(IA

S)

sizee

xclusio

nchromatograph

y(SEC

)

Asharpdecrease

inthep

heno

liccontento

bservedforreactions

involvingdirect

photolysis

SEC

areductio

nof

almost50

inthea

verage

molecular

weighto

fligninequalto

14kD

after

90min

ofirr

adiatio

n

Ksibietal[47]

Irradiationof

ligninin

the

absencea

ndpresence

ofph

otocatalystT

iO2-P2

5

UV-Visspectroscop

y13C-

nucle

armagnetic

resonance(NMR)

solid

state

totalion

gasc

hrom

atograph

y(TIC)

indu

ctioncoup

lingplasma(

ICP)

chem

icaloxygen

demand(C

OD)


TiO

2catalystaft

er420m

inreactiontim


uctsshow

edvanillin

vanillica

cidpalm

itica

cid

biph

enylstructuresand

345-trim

etho

xybenzaldehyde

presence

ofmagnesiu

mandcalcium

ions

CODremovalishigh

erforthe


ofligninsolutio

n

Kansaletal[48]

Catalystdo

sepHoxidant

concentration

initialsubstrate

concentration

ZnOcatalystin

slurryandim

mob

ilizedmod

e

UV-Visspectroscop

yCO

D

Optim

umcatalystdo

seis1gL

optim

umoxidantcon

centratio

n2times10minus6M

graduald

ecreaseo

fabsorptionpeak

indicatin

gdecompo

sitionof

organics

CODremovalishigh

erforthe


ofligninsolutio

n

Dahm

and

Lucia[

49]

Catalystdo

seillu

mination

intensity

UV-Visspectroscop

ytotalorganiccarbon

(TOC)

capillaryionelectro

phoresis

analysis(C

IA)

Gradu

aldecrease

inabsorptio

npeak

indicatin

gdecompo

sitionof

organics

optim

alcatalystdo

seof

10mgm

high

erillum

inationintensities

correlated

well

with

high


74disapp

earanceo

fTOC

Portjanskajaand

Preis[50]

Influ

ence

offerrou

sion

sN-dop

edcatalysteffect

sprayedcatalyston

supp

ortand

subm

ersedcatalyst

CODU

V-Visspectroscop

ybiochemical

oxygen

demand(BOD)colorim

etric

measurementat570

nm

Additio

nof

Fe2+upto

28m

gLleadsto25increase

inph

otocatalyticeffi

ciency


times

high

ereffi

ciency

than

theo

neattached

bysubm

ersio

nnegligibleeffecto

fN-dop

edcatalyst

increase

ofaldehyde

concentrationover

reactio

ntim

eneutralm

ediawas

mostb

eneficialforb

iodegradability

80of

freep

heno

lsremoved

undern

eutralcond

ition

s

Tanaka

etal[51]Ca

talystloadinglignin

concentration

illum

inationtim

e

UV-Visspectroscop

yTO

Cgel

perm

eatio

nchromatograph

y(G

PC)

1 HNMR

Fouriertransform

ationinfrared

(FTIR)

spectro

scop

y

FTIR


ationof

arom

aticmoietyp

resent

inlignin

characteris

ticband

sofaromaticrin

gsm

etho

xyand

aliphatic

sidec

hains

decrease

inTO

Cvalues

over

time

decrease


increase

catalystdo

sageB

utaft

ercatalystthreshold

valueisa


ausesa

decrease

indegradationrates

FTIR

peaksa

reshifted

towards

lower

molecular

weightregionaft

erph

otocatalysis

Tonu

cci

etal[33]

Testof

catalytic

syste

mstoob

tain

fractio

nswith

redu

ceddegreeso

fpo

lymerization

comparis

onof

thermalandph

otochemical

reactio

ns

1 HNMR

gasc

hrom

atograph

y-mass

spectro

scop

y(G

C-MS)

POMsa

relessselectivew

henused

asph

otocatalystsandno

appreciableb

leaching

ofthes

olutionwas

seen

whenPO

Mwas

used

asthermalcatalyst

deriv

edchem

icalsfrom

experim

entvanillin

hydroxylmetho

xy-acetoph

enon

econiferylalcoh

olcon


lform

icacidacetic

acidand

sometim

essm

allamou

ntso

fC-2

andC-

3alcoho

ls

Miyatae

tal[24]

Exam

inationof

cellwall

structureo

flignin(w

oodflo

ur)

before

andaft

erph

otocatalysis

GC-

MSscanning

electronmicroscop

y(SEM

)1 H

NMR



nedto

thes

urface

oflignin

deriv

edchem

icalse

xperim

entvanillin

Shende

etal[17]Testof

combinedactio

nof

bio-

andph

otocatalyticsyste

ms

UV-Visspectroscop

yGC-

MSX-

ray

dispersiv

eenergyspectro

scop

yandX-

ray

diffractio

nanalysis(EDX

XRD)SE

M

Detectio

nof

follo

wingchem


ethyl-2

-metho

xyph

enol

metho

xyph

enyloxim

eguaiacolsuccinica


vanillin


Table3Con

tinued

Reference

Parameter

studied

Analytic

sRe

sult

Tian

etal[52]

andPanetal

[53]

Testof

combinedactio

nof

electro-and

photocatalytic

syste

ms

UV-Visspectroscop

yFT

IRSEM

X-ray

(EDX)

highperfo

rmance

liquid

chromatograph

y(H

PLC)

COD

Detectio

nof

thefollowingchem

icalscarbon

ylfunctio

nalityvanillin

andvanillica

cid

Awun

gacha

Lekeleface

tal

[54][55]

Com

paris

onof

degradationrates

bydifferent

catalyst

HPL

Cflu

orescencea

ndUV-Vis

spectro

scop

ySE

MT

OC


rdegradatio

nof

thea

liphatic

moietycomparedto

the

arom

aticmoietyof

ligninsulfonateob

tained

from

paperw

astewaterPeaks

observed

durin

gHPL

Canalysis

Someo

fthe

peaksp

rodu

cedaft

erph

otocatalysishad

fluorescences

ignals

Thissuggeststhep

rodu

ctionof

newsubstances

andflu

orop

hores

Coatin

gsprod

uced

throug

hSol-G

elprocedures

arestablea

ndcanbe

used

manytim

es



2as





2




2possesses










2to glass






2gel or TiO

2particles






2





(10 gL TiO2)











2


2-P25-SiO

2catalyst with Pt













2









2or PtTiO

2




2


HO2

∙999445999468 H+ + ∙O

2


See [76]∙O2



2



2





2














200 220 240 260 280 300 320 340 360

00

05

10

15

20

25

Abso

rban

ce

Wavelength (nm)0min

30min

60min

120min

180min

300min

360min

420min

1200min



2-P25-SiO

2)

[54]






2-



2O and NH

3 Total organic



2and H





2-P25-SiO





0 200 400 600 800 1000 12000

50

100

150

200

250

Diss

olve

d ca

rbon

(ppm

)

t (min)

TiO2-P25-SiO2


ZnO + TiO2-P25-SiO2

No coating UV light


2-P25-SiO

2+Pt TiO

2-P25-SiO

2


2-P25-SiO

2) [54]




























2O2) up to at




2O2














Acknowledgments


References
























































A vol 154 no 2-3 pp 211ndash218 2003
















2as














2aqueous suspen-










2










































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


1

2

3

45

120572120573

120574OH

OH

p-Coumaryl alcohol

OCH3

OH

OH


OCH3H3CO

OH

OH














2(h+VB)



2 respectively



Spirodienone

O

OO

O

O

OHO

OO

O

O

O

O

OHO

O

O

O

O

O

O

OO O

O

O

O

O

O

O

O

OH

OO

OO

O

O

OO




HO

OAr

HO

OH

OHOH

OH

HO

HO

OH

HO

OH

HO

OH

HO

OH

HO

OH

HO

OH

HO

OH

HO

OH

HO4-O-5

OH

HOOH

120573-120573

5-5998400

120573-O-4

120573-1

120573-1

O


O2∙minus + H+ HO2

∙

2HO2∙

HO∙ + OHminus

∙OH


S∙+ + O2SO2

∙+

O2∙minus

∙O2minus



O2 + eminus

H2O2 + O2

H2O2 + eminus


h+ + OHminus

Electron capture

Recombination

eminus

h+

Conduction band

Valence band

Electron release

eminus

O2

(super oxide)

Light

OHminus




2O producing




TiO2


2(

eminusCBh+VB) (1)

TiO2(h+) +H

2O 997888rarr TiO

2+HO∙ +H+ (2)



MeO MeOMeOMeO

∙OO

O

O ∙

OH

HO+ +


RH

bond cleavage

Vanillin

O

OO

O

OO O

O

O

O

O

O

HO HO

HOHO

HO

HO

HO HO

OH OH

HO

OCH3

OCH3

OCH3

OCH3

OCH3 OCH3

OCH3

OCH3 OCH3

OCH3

h minusH∙OH∙∙

O2TiO2

HminusOH∙

C120572-C120573

∙



2

∙+ (4)


2+∙S+ (5)

TiO2(eminus) +O

2997888rarr TiO

2+∙O2

minus (6)

HO∙ + ∙O2

minus


(7)

TiO2(eminus) + TiO

2(h+) 997888rarr heat (8)









Adlerol


Enzyme1

23

4

4

1

2

3

5

5

6

6

Guaiacol

Veratraldehyde

Ketone

O

OO

O

O O

O

O

O

HO

HOHO

HO

OCH3

OCH3

OCH3

OCH3

OCH3

OCH3

120572120573

120574

minusH+

∙+

∙

∙+


O2

120572 120573

120574

HOHOHO

OCH3

OCH3OCH3

OCH3 OCH3

OCH3

OCH3

120572120572

120573 120573

120573

120574 120574

HO

HO

120574

OCH3

120573

HO

HO

120574

HO

OCH3

OCH3

OCH3

120572120573

120574







rutile TiO2[49] TiO


a few


Table2Summaryof

startingcond

ition

sfor

thep

hotocatalytic

degradationof

lignin

Reference

Lign

insource

Catalyst

Reactio

ncond

ition

s

MacHadoetal[42]

Peroxyform

icacid

lignins

from

eucalyptus

grandisw

ood(EL1)

EL1+

sodium

borohydride

TiO

2andH

2O2

Lign

inconcentration

025

mgmL119879=25∘C

pH11U

VVisradiatio

n120582gt300nm

40

0Wmercury

lampcylin

dricalPy

rexglassreactorcon

stanto

xygenbu

bblin

g

Ksibietal[47]

Water

solubleligninob

tained

from

blackliq

uor

TiO

2-P2

5(D

egussa)

Lign

inconcentration

90mgL119879=20∘C


pyrex

reactoro

pento

airPh

ilips

HPK

125W

lamp

Kansaletal[48]

Lign

infro

mwheatstr

awkraft

digestion

TiO

2-P2

5(D

egussa)a

ndZn

O

Lign

inconcentration

10ndash100

mgLin

100m

LZn

Ocatalystdo

se(05ndash20gL)pH

ofthes


mination

oxidantcon

centratio

n306times10minus6M


slurrypo


hypo

chlorite

solutio

n(4availableC

l 2)

Dahm

andLu

cia[

49]

Whitewater

from

indu

strialprocess

water

thatexits

inpaperm

achines

FischerS

cientifi

crutile

TiO

2

Lign

inconcentration

40mgLin

500m


42∘C

Rayonet

photochemicalcham

ber16

VWR8-W

blacklightpho

spho

r(350-nm

)lam

ps

constant

oxygen

bubb

lingpo

wer

ofillum

ination

128to

64Wlight

intensity

223ndash44

5mWcm

3

Portjanskajaand

Preis[50]

Lign

inpurchased

from

Aldric

hTiO

2P2

5-N(D

egussa)

Lign

inconcentration

100m

gLpH


open

toair

PhillipsT


inescent

mercury

UV-lampUV-radiation

120582gt360nm

pow

erdensity

ofirr

adiatio

n=07m

Wcm

2 visib

lelight

source

Tanaka

etal[51]

Lign

infro

mconiferous

woo

dTiO

2(TiO

2mdashTP

-2of

Fujititan)

Lign

inconcentration

0003to

003U


cylindrical

reactio

nvessel

Tonu

ccietal[33]

Ca2+andNH4

+ligninderiv

atives

TiO

2as

Degussa

P25

+po

lyoxom

etalates

(POM)H

2O2

Openqu

artztubes(20

mL)


1atm

multirayso

ften

UVlamps

of15W

power

eachU


Miyatae

tal[24]

Piceag

lehn

iiwoo

dflo

urTiO

2po

lyethylene

oxide(PE

O)

Reactorop

enpetrid

ish119879=30∘C119905=48h40

0Wmercury

lamp

Shende

etal[17]

Kraft

lignin

TiO

2-Zn

O-ZrO

2Lign

inconcentration

1mgmLin

10mL250W

Xeno

nlampandAM

15Glamp

filterpo

wer

density

ofirr

adiatio

n100m

Wcm

2 solarlam

psim

ulator

Tian

etal[52]

andPanetal[53]

Kraft

ligninfro

mblackliq

uor

Ta2O

5-IrO

2andPb

O2thin

film

TiO

2nano

tubePbO

2

Lign

inconcentration

30(w


119905=10minpow

erdensity

ofirr

adiatio

n20

mWcm

2 blue

waveT

M50

ASUVspot

lampEG

ampG2273

potentiosta

tgalvano


2NTPb

O2ele

ctrode

asworking

electrode

andPt

coilas

outere

lectrode

andAgAgC

lasreference

electrode

Awun

gachaL

ekele

fac

etal[54][55]

Lign

insulfo

natefro

mpaperw

aste

water

TiO

2as

Degussa

P25

TiO

2fro

msol-g

elprocesso

fTiOSO

4TT

IP

Lign

inconcentration

500m

gLin

200m

LOsram

Planon

light

sourceirradiance

30ndash4

0Wm


20nm

119905=20hreactoro

pento

air

recirculationsyste

mflow

rate225mLmin



dsand

results

from

different

workgrou

ps

Reference

Parameter

studied

Analytic

sRe

sult

MacHado

etal[42]

Roleof

hydroxylradicals

irradiatio

nof

ligninin

the

absencea

ndpresence

ofph

otocatalystT

iO2andH

2O2

Ultraviolet-v


scop

yionizatio

nabsorptio

nspectro

scop

y(IA

S)

sizee

xclusio

nchromatograph

y(SEC

)

Asharpdecrease

inthep

heno

liccontento

bservedforreactions

involvingdirect

photolysis

SEC

areductio

nof

almost50

inthea

verage

molecular

weighto

fligninequalto

14kD

after

90min

ofirr

adiatio

n

Ksibietal[47]

Irradiationof

ligninin

the

absencea

ndpresence

ofph

otocatalystT

iO2-P2

5

UV-Visspectroscop

y13C-

nucle

armagnetic

resonance(NMR)

solid

state

totalion

gasc

hrom

atograph

y(TIC)

indu

ctioncoup

lingplasma(

ICP)

chem

icaloxygen

demand(C

OD)


TiO

2catalystaft

er420m

inreactiontim


uctsshow

edvanillin

vanillica

cidpalm

itica

cid

biph

enylstructuresand

345-trim

etho

xybenzaldehyde

presence

ofmagnesiu

mandcalcium

ions

CODremovalishigh

erforthe


ofligninsolutio

n

Kansaletal[48]

Catalystdo

sepHoxidant

concentration

initialsubstrate

concentration

ZnOcatalystin

slurryandim

mob

ilizedmod

e

UV-Visspectroscop

yCO

D

Optim

umcatalystdo

seis1gL

optim

umoxidantcon

centratio

n2times10minus6M

graduald

ecreaseo

fabsorptionpeak

indicatin

gdecompo

sitionof

organics

CODremovalishigh

erforthe


ofligninsolutio

n

Dahm

and

Lucia[

49]

Catalystdo

seillu

mination

intensity

UV-Visspectroscop

ytotalorganiccarbon

(TOC)

capillaryionelectro

phoresis

analysis(C

IA)

Gradu

aldecrease

inabsorptio

npeak

indicatin

gdecompo

sitionof

organics

optim

alcatalystdo

seof

10mgm

high

erillum

inationintensities

correlated

well

with

high


74disapp

earanceo

fTOC

Portjanskajaand

Preis[50]

Influ

ence

offerrou

sion

sN-dop

edcatalysteffect

sprayedcatalyston

supp

ortand

subm

ersedcatalyst

CODU

V-Visspectroscop

ybiochemical

oxygen

demand(BOD)colorim

etric

measurementat570

nm

Additio

nof

Fe2+upto

28m

gLleadsto25increase

inph

otocatalyticeffi

ciency


times

high

ereffi

ciency

than

theo

neattached

bysubm

ersio

nnegligibleeffecto

fN-dop

edcatalyst

increase

ofaldehyde

concentrationover

reactio

ntim

eneutralm

ediawas

mostb

eneficialforb

iodegradability

80of

freep

heno

lsremoved

undern

eutralcond

ition

s

Tanaka

etal[51]Ca

talystloadinglignin

concentration

illum

inationtim

e

UV-Visspectroscop

yTO

Cgel

perm

eatio

nchromatograph

y(G

PC)

1 HNMR

Fouriertransform

ationinfrared

(FTIR)

spectro

scop

y

FTIR


ationof

arom

aticmoietyp

resent

inlignin

characteris

ticband

sofaromaticrin

gsm

etho

xyand

aliphatic

sidec

hains

decrease

inTO

Cvalues

over

time

decrease


increase

catalystdo

sageB

utaft

ercatalystthreshold

valueisa


ausesa

decrease

indegradationrates

FTIR

peaksa

reshifted

towards

lower

molecular

weightregionaft

erph

otocatalysis

Tonu

cci

etal[33]

Testof

catalytic

syste

mstoob

tain

fractio

nswith

redu

ceddegreeso

fpo

lymerization

comparis

onof

thermalandph

otochemical

reactio

ns

1 HNMR

gasc

hrom

atograph

y-mass

spectro

scop

y(G

C-MS)

POMsa

relessselectivew

henused

asph

otocatalystsandno

appreciableb

leaching

ofthes

olutionwas

seen

whenPO

Mwas

used

asthermalcatalyst

deriv

edchem

icalsfrom

experim

entvanillin

hydroxylmetho

xy-acetoph

enon

econiferylalcoh

olcon


lform

icacidacetic

acidand

sometim

essm

allamou

ntso

fC-2

andC-

3alcoho

ls

Miyatae

tal[24]

Exam

inationof

cellwall

structureo

flignin(w

oodflo

ur)

before

andaft

erph

otocatalysis

GC-

MSscanning

electronmicroscop

y(SEM

)1 H

NMR



nedto

thes

urface

oflignin

deriv

edchem

icalse

xperim

entvanillin

Shende

etal[17]Testof

combinedactio

nof

bio-

andph

otocatalyticsyste

ms

UV-Visspectroscop

yGC-

MSX-

ray

dispersiv

eenergyspectro

scop

yandX-

ray

diffractio

nanalysis(EDX

XRD)SE

M

Detectio

nof

follo

wingchem


ethyl-2

-metho

xyph

enol

metho

xyph

enyloxim

eguaiacolsuccinica


vanillin


Table3Con

tinued

Reference

Parameter

studied

Analytic

sRe

sult

Tian

etal[52]

andPanetal

[53]

Testof

combinedactio

nof

electro-and

photocatalytic

syste

ms

UV-Visspectroscop

yFT

IRSEM

X-ray

(EDX)

highperfo

rmance

liquid

chromatograph

y(H

PLC)

COD

Detectio

nof

thefollowingchem

icalscarbon

ylfunctio

nalityvanillin

andvanillica

cid

Awun

gacha

Lekeleface

tal

[54][55]

Com

paris

onof

degradationrates

bydifferent

catalyst

HPL

Cflu

orescencea

ndUV-Vis

spectro

scop

ySE

MT

OC


rdegradatio

nof

thea

liphatic

moietycomparedto

the

arom

aticmoietyof

ligninsulfonateob

tained

from

paperw

astewaterPeaks

observed

durin

gHPL

Canalysis

Someo

fthe

peaksp

rodu

cedaft

erph

otocatalysishad

fluorescences

ignals

Thissuggeststhep

rodu

ctionof

newsubstances

andflu

orop

hores

Coatin

gsprod

uced

throug

hSol-G

elprocedures

arestablea

ndcanbe

used

manytim

es



2as





2




2possesses










2to glass






2gel or TiO

2particles






2





(10 gL TiO2)











2


2-P25-SiO

2catalyst with Pt













2









2or PtTiO

2




2


HO2

∙999445999468 H+ + ∙O

2


See [76]∙O2



2



2





2














200 220 240 260 280 300 320 340 360

00

05

10

15

20

25

Abso

rban

ce

Wavelength (nm)0min

30min

60min

120min

180min

300min

360min

420min

1200min



2-P25-SiO

2)

[54]






2-



2O and NH

3 Total organic



2and H





2-P25-SiO





0 200 400 600 800 1000 12000

50

100

150

200

250

Diss

olve

d ca

rbon

(ppm

)

t (min)

TiO2-P25-SiO2


ZnO + TiO2-P25-SiO2

No coating UV light


2-P25-SiO

2+Pt TiO

2-P25-SiO

2


2-P25-SiO

2) [54]




























2O2) up to at




2O2














Acknowledgments


References
























































A vol 154 no 2-3 pp 211ndash218 2003
















2as














2aqueous suspen-










2










































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


Spirodienone

O

OO

O

O

OHO

OO

O

O

O

O

OHO

O

O

O

O

O

O

OO O

O

O

O

O

O

O

O

OH

OO

OO

O

O

OO




HO

OAr

HO

OH

OHOH

OH

HO

HO

OH

HO

OH

HO

OH

HO

OH

HO

OH

HO

OH

HO

OH

HO

OH

HO4-O-5

OH

HOOH

120573-120573

5-5998400

120573-O-4

120573-1

120573-1

O


O2∙minus + H+ HO2

∙

2HO2∙

HO∙ + OHminus

∙OH


S∙+ + O2SO2

∙+

O2∙minus

∙O2minus



O2 + eminus

H2O2 + O2

H2O2 + eminus


h+ + OHminus

Electron capture

Recombination

eminus

h+

Conduction band

Valence band

Electron release

eminus

O2

(super oxide)

Light

OHminus




2O producing




TiO2


2(

eminusCBh+VB) (1)

TiO2(h+) +H

2O 997888rarr TiO

2+HO∙ +H+ (2)



MeO MeOMeOMeO

∙OO

O

O ∙

OH

HO+ +


RH

bond cleavage

Vanillin

O

OO

O

OO O

O

O

O

O

O

HO HO

HOHO

HO

HO

HO HO

OH OH

HO

OCH3

OCH3

OCH3

OCH3

OCH3 OCH3

OCH3

OCH3 OCH3

OCH3

h minusH∙OH∙∙

O2TiO2

HminusOH∙

C120572-C120573

∙



2

∙+ (4)


2+∙S+ (5)

TiO2(eminus) +O

2997888rarr TiO

2+∙O2

minus (6)

HO∙ + ∙O2

minus


(7)

TiO2(eminus) + TiO

2(h+) 997888rarr heat (8)









Adlerol


Enzyme1

23

4

4

1

2

3

5

5

6

6

Guaiacol

Veratraldehyde

Ketone

O

OO

O

O O

O

O

O

HO

HOHO

HO

OCH3

OCH3

OCH3

OCH3

OCH3

OCH3

120572120573

120574

minusH+

∙+

∙

∙+


O2

120572 120573

120574

HOHOHO

OCH3

OCH3OCH3

OCH3 OCH3

OCH3

OCH3

120572120572

120573 120573

120573

120574 120574

HO

HO

120574

OCH3

120573

HO

HO

120574

HO

OCH3

OCH3

OCH3

120572120573

120574







rutile TiO2[49] TiO


a few


Table2Summaryof

startingcond

ition

sfor

thep

hotocatalytic

degradationof

lignin

Reference

Lign

insource

Catalyst

Reactio

ncond

ition

s

MacHadoetal[42]

Peroxyform

icacid

lignins

from

eucalyptus

grandisw

ood(EL1)

EL1+

sodium

borohydride

TiO

2andH

2O2

Lign

inconcentration

025

mgmL119879=25∘C

pH11U

VVisradiatio

n120582gt300nm

40

0Wmercury

lampcylin

dricalPy

rexglassreactorcon

stanto

xygenbu

bblin

g

Ksibietal[47]

Water

solubleligninob

tained

from

blackliq

uor

TiO

2-P2

5(D

egussa)

Lign

inconcentration

90mgL119879=20∘C


pyrex

reactoro

pento

airPh

ilips

HPK

125W

lamp

Kansaletal[48]

Lign

infro

mwheatstr

awkraft

digestion

TiO

2-P2

5(D

egussa)a

ndZn

O

Lign

inconcentration

10ndash100

mgLin

100m

LZn

Ocatalystdo

se(05ndash20gL)pH

ofthes


mination

oxidantcon

centratio

n306times10minus6M


slurrypo


hypo

chlorite

solutio

n(4availableC

l 2)

Dahm

andLu

cia[

49]

Whitewater

from

indu

strialprocess

water

thatexits

inpaperm

achines

FischerS

cientifi

crutile

TiO

2

Lign

inconcentration

40mgLin

500m


42∘C

Rayonet

photochemicalcham

ber16

VWR8-W

blacklightpho

spho

r(350-nm

)lam

ps

constant

oxygen

bubb

lingpo

wer

ofillum

ination

128to

64Wlight

intensity

223ndash44

5mWcm

3

Portjanskajaand

Preis[50]

Lign

inpurchased

from

Aldric

hTiO

2P2

5-N(D

egussa)

Lign

inconcentration

100m

gLpH


open

toair

PhillipsT


inescent

mercury

UV-lampUV-radiation

120582gt360nm

pow

erdensity

ofirr

adiatio

n=07m

Wcm

2 visib

lelight

source

Tanaka

etal[51]

Lign

infro

mconiferous

woo

dTiO

2(TiO

2mdashTP

-2of

Fujititan)

Lign

inconcentration

0003to

003U


cylindrical

reactio

nvessel

Tonu

ccietal[33]

Ca2+andNH4

+ligninderiv

atives

TiO

2as

Degussa

P25

+po

lyoxom

etalates

(POM)H

2O2

Openqu

artztubes(20

mL)


1atm

multirayso

ften

UVlamps

of15W

power

eachU


Miyatae

tal[24]

Piceag

lehn

iiwoo

dflo

urTiO

2po

lyethylene

oxide(PE

O)

Reactorop

enpetrid

ish119879=30∘C119905=48h40

0Wmercury

lamp

Shende

etal[17]

Kraft

lignin

TiO

2-Zn

O-ZrO

2Lign

inconcentration

1mgmLin

10mL250W

Xeno

nlampandAM

15Glamp

filterpo

wer

density

ofirr

adiatio

n100m

Wcm

2 solarlam

psim

ulator

Tian

etal[52]

andPanetal[53]

Kraft

ligninfro

mblackliq

uor

Ta2O

5-IrO

2andPb

O2thin

film

TiO

2nano

tubePbO

2

Lign

inconcentration

30(w


119905=10minpow

erdensity

ofirr

adiatio

n20

mWcm

2 blue

waveT

M50

ASUVspot

lampEG

ampG2273

potentiosta

tgalvano


2NTPb

O2ele

ctrode

asworking

electrode

andPt

coilas

outere

lectrode

andAgAgC

lasreference

electrode

Awun

gachaL

ekele

fac

etal[54][55]

Lign

insulfo

natefro

mpaperw

aste

water

TiO

2as

Degussa

P25

TiO

2fro

msol-g

elprocesso

fTiOSO

4TT

IP

Lign

inconcentration

500m

gLin

200m

LOsram

Planon

light

sourceirradiance

30ndash4

0Wm


20nm

119905=20hreactoro

pento

air

recirculationsyste

mflow

rate225mLmin



dsand

results

from

different

workgrou

ps

Reference

Parameter

studied

Analytic

sRe

sult

MacHado

etal[42]

Roleof

hydroxylradicals

irradiatio

nof

ligninin

the

absencea

ndpresence

ofph

otocatalystT

iO2andH

2O2

Ultraviolet-v


scop

yionizatio

nabsorptio

nspectro

scop

y(IA

S)

sizee

xclusio

nchromatograph

y(SEC

)

Asharpdecrease

inthep

heno

liccontento

bservedforreactions

involvingdirect

photolysis

SEC

areductio

nof

almost50

inthea

verage

molecular

weighto

fligninequalto

14kD

after

90min

ofirr

adiatio

n

Ksibietal[47]

Irradiationof

ligninin

the

absencea

ndpresence

ofph

otocatalystT

iO2-P2

5

UV-Visspectroscop

y13C-

nucle

armagnetic

resonance(NMR)

solid

state

totalion

gasc

hrom

atograph

y(TIC)

indu

ctioncoup

lingplasma(

ICP)

chem

icaloxygen

demand(C

OD)


TiO

2catalystaft

er420m

inreactiontim


uctsshow

edvanillin

vanillica

cidpalm

itica

cid

biph

enylstructuresand

345-trim

etho

xybenzaldehyde

presence

ofmagnesiu

mandcalcium

ions

CODremovalishigh

erforthe


ofligninsolutio

n

Kansaletal[48]

Catalystdo

sepHoxidant

concentration

initialsubstrate

concentration

ZnOcatalystin

slurryandim

mob

ilizedmod

e

UV-Visspectroscop

yCO

D

Optim

umcatalystdo

seis1gL

optim

umoxidantcon

centratio

n2times10minus6M

graduald

ecreaseo

fabsorptionpeak

indicatin

gdecompo

sitionof

organics

CODremovalishigh

erforthe


ofligninsolutio

n

Dahm

and

Lucia[

49]

Catalystdo

seillu

mination

intensity

UV-Visspectroscop

ytotalorganiccarbon

(TOC)

capillaryionelectro

phoresis

analysis(C

IA)

Gradu

aldecrease

inabsorptio

npeak

indicatin

gdecompo

sitionof

organics

optim

alcatalystdo

seof

10mgm

high

erillum

inationintensities

correlated

well

with

high


74disapp

earanceo

fTOC

Portjanskajaand

Preis[50]

Influ

ence

offerrou

sion

sN-dop

edcatalysteffect

sprayedcatalyston

supp

ortand

subm

ersedcatalyst

CODU

V-Visspectroscop

ybiochemical

oxygen

demand(BOD)colorim

etric

measurementat570

nm

Additio

nof

Fe2+upto

28m

gLleadsto25increase

inph

otocatalyticeffi

ciency


times

high

ereffi

ciency

than

theo

neattached

bysubm

ersio

nnegligibleeffecto

fN-dop

edcatalyst

increase

ofaldehyde

concentrationover

reactio

ntim

eneutralm

ediawas

mostb

eneficialforb

iodegradability

80of

freep

heno

lsremoved

undern

eutralcond

ition

s

Tanaka

etal[51]Ca

talystloadinglignin

concentration

illum

inationtim

e

UV-Visspectroscop

yTO

Cgel

perm

eatio

nchromatograph

y(G

PC)

1 HNMR

Fouriertransform

ationinfrared

(FTIR)

spectro

scop

y

FTIR


ationof

arom

aticmoietyp

resent

inlignin

characteris

ticband

sofaromaticrin

gsm

etho

xyand

aliphatic

sidec

hains

decrease

inTO

Cvalues

over

time

decrease


increase

catalystdo

sageB

utaft

ercatalystthreshold

valueisa


ausesa

decrease

indegradationrates

FTIR

peaksa

reshifted

towards

lower

molecular

weightregionaft

erph

otocatalysis

Tonu

cci

etal[33]

Testof

catalytic

syste

mstoob

tain

fractio

nswith

redu

ceddegreeso

fpo

lymerization

comparis

onof

thermalandph

otochemical

reactio

ns

1 HNMR

gasc

hrom

atograph

y-mass

spectro

scop

y(G

C-MS)

POMsa

relessselectivew

henused

asph

otocatalystsandno

appreciableb

leaching

ofthes

olutionwas

seen

whenPO

Mwas

used

asthermalcatalyst

deriv

edchem

icalsfrom

experim

entvanillin

hydroxylmetho

xy-acetoph

enon

econiferylalcoh

olcon


lform

icacidacetic

acidand

sometim

essm

allamou

ntso

fC-2

andC-

3alcoho

ls

Miyatae

tal[24]

Exam

inationof

cellwall

structureo

flignin(w

oodflo

ur)

before

andaft

erph

otocatalysis

GC-

MSscanning

electronmicroscop

y(SEM

)1 H

NMR



nedto

thes

urface

oflignin

deriv

edchem

icalse

xperim

entvanillin

Shende

etal[17]Testof

combinedactio

nof

bio-

andph

otocatalyticsyste

ms

UV-Visspectroscop

yGC-

MSX-

ray

dispersiv

eenergyspectro

scop

yandX-

ray

diffractio

nanalysis(EDX

XRD)SE

M

Detectio

nof

follo

wingchem


ethyl-2

-metho

xyph

enol

metho

xyph

enyloxim

eguaiacolsuccinica


vanillin


Table3Con

tinued

Reference

Parameter

studied

Analytic

sRe

sult

Tian

etal[52]

andPanetal

[53]

Testof

combinedactio

nof

electro-and

photocatalytic

syste

ms

UV-Visspectroscop

yFT

IRSEM

X-ray

(EDX)

highperfo

rmance

liquid

chromatograph

y(H

PLC)

COD

Detectio

nof

thefollowingchem

icalscarbon

ylfunctio

nalityvanillin

andvanillica

cid

Awun

gacha

Lekeleface

tal

[54][55]

Com

paris

onof

degradationrates

bydifferent

catalyst

HPL

Cflu

orescencea

ndUV-Vis

spectro

scop

ySE

MT

OC


rdegradatio

nof

thea

liphatic

moietycomparedto

the

arom

aticmoietyof

ligninsulfonateob

tained

from

paperw

astewaterPeaks

observed

durin

gHPL

Canalysis

Someo

fthe

peaksp

rodu

cedaft

erph

otocatalysishad

fluorescences

ignals

Thissuggeststhep

rodu

ctionof

newsubstances

andflu

orop

hores

Coatin

gsprod

uced

throug

hSol-G

elprocedures

arestablea

ndcanbe

used

manytim

es



2as





2




2possesses










2to glass






2gel or TiO

2particles






2





(10 gL TiO2)











2


2-P25-SiO

2catalyst with Pt













2









2or PtTiO

2




2


HO2

∙999445999468 H+ + ∙O

2


See [76]∙O2



2



2





2














200 220 240 260 280 300 320 340 360

00

05

10

15

20

25

Abso

rban

ce

Wavelength (nm)0min

30min

60min

120min

180min

300min

360min

420min

1200min



2-P25-SiO

2)

[54]






2-



2O and NH

3 Total organic



2and H





2-P25-SiO





0 200 400 600 800 1000 12000

50

100

150

200

250

Diss

olve

d ca

rbon

(ppm

)

t (min)

TiO2-P25-SiO2


ZnO + TiO2-P25-SiO2

No coating UV light


2-P25-SiO

2+Pt TiO

2-P25-SiO

2


2-P25-SiO

2) [54]




























2O2) up to at




2O2














Acknowledgments


References
























































A vol 154 no 2-3 pp 211ndash218 2003
















2as














2aqueous suspen-










2










































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


MeO MeOMeOMeO

∙OO

O

O ∙

OH

HO+ +


RH

bond cleavage

Vanillin

O

OO

O

OO O

O

O

O

O

O

HO HO

HOHO

HO

HO

HO HO

OH OH

HO

OCH3

OCH3

OCH3

OCH3

OCH3 OCH3

OCH3

OCH3 OCH3

OCH3

h minusH∙OH∙∙

O2TiO2

HminusOH∙

C120572-C120573

∙



2

∙+ (4)


2+∙S+ (5)

TiO2(eminus) +O

2997888rarr TiO

2+∙O2

minus (6)

HO∙ + ∙O2

minus


(7)

TiO2(eminus) + TiO

2(h+) 997888rarr heat (8)









Adlerol


Enzyme1

23

4

4

1

2

3

5

5

6

6

Guaiacol

Veratraldehyde

Ketone

O

OO

O

O O

O

O

O

HO

HOHO

HO

OCH3

OCH3

OCH3

OCH3

OCH3

OCH3

120572120573

120574

minusH+

∙+

∙

∙+


O2

120572 120573

120574

HOHOHO

OCH3

OCH3OCH3

OCH3 OCH3

OCH3

OCH3

120572120572

120573 120573

120573

120574 120574

HO

HO

120574

OCH3

120573

HO

HO

120574

HO

OCH3

OCH3

OCH3

120572120573

120574







rutile TiO2[49] TiO


a few


Table2Summaryof

startingcond

ition

sfor

thep

hotocatalytic

degradationof

lignin

Reference

Lign

insource

Catalyst

Reactio

ncond

ition

s

MacHadoetal[42]

Peroxyform

icacid

lignins

from

eucalyptus

grandisw

ood(EL1)

EL1+

sodium

borohydride

TiO

2andH

2O2

Lign

inconcentration

025

mgmL119879=25∘C

pH11U

VVisradiatio

n120582gt300nm

40

0Wmercury

lampcylin

dricalPy

rexglassreactorcon

stanto

xygenbu

bblin

g

Ksibietal[47]

Water

solubleligninob

tained

from

blackliq

uor

TiO

2-P2

5(D

egussa)

Lign

inconcentration

90mgL119879=20∘C


pyrex

reactoro

pento

airPh

ilips

HPK

125W

lamp

Kansaletal[48]

Lign

infro

mwheatstr

awkraft

digestion

TiO

2-P2

5(D

egussa)a

ndZn

O

Lign

inconcentration

10ndash100

mgLin

100m

LZn

Ocatalystdo

se(05ndash20gL)pH

ofthes


mination

oxidantcon

centratio

n306times10minus6M


slurrypo


hypo

chlorite

solutio

n(4availableC

l 2)

Dahm

andLu

cia[

49]

Whitewater

from

indu

strialprocess

water

thatexits

inpaperm

achines

FischerS

cientifi

crutile

TiO

2

Lign

inconcentration

40mgLin

500m


42∘C

Rayonet

photochemicalcham

ber16

VWR8-W

blacklightpho

spho

r(350-nm

)lam

ps

constant

oxygen

bubb

lingpo

wer

ofillum

ination

128to

64Wlight

intensity

223ndash44

5mWcm

3

Portjanskajaand

Preis[50]

Lign

inpurchased

from

Aldric

hTiO

2P2

5-N(D

egussa)

Lign

inconcentration

100m

gLpH


open

toair

PhillipsT


inescent

mercury

UV-lampUV-radiation

120582gt360nm

pow

erdensity

ofirr

adiatio

n=07m

Wcm

2 visib

lelight

source

Tanaka

etal[51]

Lign

infro

mconiferous

woo

dTiO

2(TiO

2mdashTP

-2of

Fujititan)

Lign

inconcentration

0003to

003U


cylindrical

reactio

nvessel

Tonu

ccietal[33]

Ca2+andNH4

+ligninderiv

atives

TiO

2as

Degussa

P25

+po

lyoxom

etalates

(POM)H

2O2

Openqu

artztubes(20

mL)


1atm

multirayso

ften

UVlamps

of15W

power

eachU


Miyatae

tal[24]

Piceag

lehn

iiwoo

dflo

urTiO

2po

lyethylene

oxide(PE

O)

Reactorop

enpetrid

ish119879=30∘C119905=48h40

0Wmercury

lamp

Shende

etal[17]

Kraft

lignin

TiO

2-Zn

O-ZrO

2Lign

inconcentration

1mgmLin

10mL250W

Xeno

nlampandAM

15Glamp

filterpo

wer

density

ofirr

adiatio

n100m

Wcm

2 solarlam

psim

ulator

Tian

etal[52]

andPanetal[53]

Kraft

ligninfro

mblackliq

uor

Ta2O

5-IrO

2andPb

O2thin

film

TiO

2nano

tubePbO

2

Lign

inconcentration

30(w


119905=10minpow

erdensity

ofirr

adiatio

n20

mWcm

2 blue

waveT

M50

ASUVspot

lampEG

ampG2273

potentiosta

tgalvano


2NTPb

O2ele

ctrode

asworking

electrode

andPt

coilas

outere

lectrode

andAgAgC

lasreference

electrode

Awun

gachaL

ekele

fac

etal[54][55]

Lign

insulfo

natefro

mpaperw

aste

water

TiO

2as

Degussa

P25

TiO

2fro

msol-g

elprocesso

fTiOSO

4TT

IP

Lign

inconcentration

500m

gLin

200m

LOsram

Planon

light

sourceirradiance

30ndash4

0Wm


20nm

119905=20hreactoro

pento

air

recirculationsyste

mflow

rate225mLmin



dsand

results

from

different

workgrou

ps

Reference

Parameter

studied

Analytic

sRe

sult

MacHado

etal[42]

Roleof

hydroxylradicals

irradiatio

nof

ligninin

the

absencea

ndpresence

ofph

otocatalystT

iO2andH

2O2

Ultraviolet-v


scop

yionizatio

nabsorptio

nspectro

scop

y(IA

S)

sizee

xclusio

nchromatograph

y(SEC

)

Asharpdecrease

inthep

heno

liccontento

bservedforreactions

involvingdirect

photolysis

SEC

areductio

nof

almost50

inthea

verage

molecular

weighto

fligninequalto

14kD

after

90min

ofirr

adiatio

n

Ksibietal[47]

Irradiationof

ligninin

the

absencea

ndpresence

ofph

otocatalystT

iO2-P2

5

UV-Visspectroscop

y13C-

nucle

armagnetic

resonance(NMR)

solid

state

totalion

gasc

hrom

atograph

y(TIC)

indu

ctioncoup

lingplasma(

ICP)

chem

icaloxygen

demand(C

OD)


TiO

2catalystaft

er420m

inreactiontim


uctsshow

edvanillin

vanillica

cidpalm

itica

cid

biph

enylstructuresand

345-trim

etho

xybenzaldehyde

presence

ofmagnesiu

mandcalcium

ions

CODremovalishigh

erforthe


ofligninsolutio

n

Kansaletal[48]

Catalystdo

sepHoxidant

concentration

initialsubstrate

concentration

ZnOcatalystin

slurryandim

mob

ilizedmod

e

UV-Visspectroscop

yCO

D

Optim

umcatalystdo

seis1gL

optim

umoxidantcon

centratio

n2times10minus6M

graduald

ecreaseo

fabsorptionpeak

indicatin

gdecompo

sitionof

organics

CODremovalishigh

erforthe


ofligninsolutio

n

Dahm

and

Lucia[

49]

Catalystdo

seillu

mination

intensity

UV-Visspectroscop

ytotalorganiccarbon

(TOC)

capillaryionelectro

phoresis

analysis(C

IA)

Gradu

aldecrease

inabsorptio

npeak

indicatin

gdecompo

sitionof

organics

optim

alcatalystdo

seof

10mgm

high

erillum

inationintensities

correlated

well

with

high


74disapp

earanceo

fTOC

Portjanskajaand

Preis[50]

Influ

ence

offerrou

sion

sN-dop

edcatalysteffect

sprayedcatalyston

supp

ortand

subm

ersedcatalyst

CODU

V-Visspectroscop

ybiochemical

oxygen

demand(BOD)colorim

etric

measurementat570

nm

Additio

nof

Fe2+upto

28m

gLleadsto25increase

inph

otocatalyticeffi

ciency


times

high

ereffi

ciency

than

theo

neattached

bysubm

ersio

nnegligibleeffecto

fN-dop

edcatalyst

increase

ofaldehyde

concentrationover

reactio

ntim

eneutralm

ediawas

mostb

eneficialforb

iodegradability

80of

freep

heno

lsremoved

undern

eutralcond

ition

s

Tanaka

etal[51]Ca

talystloadinglignin

concentration

illum

inationtim

e

UV-Visspectroscop

yTO

Cgel

perm

eatio

nchromatograph

y(G

PC)

1 HNMR

Fouriertransform

ationinfrared

(FTIR)

spectro

scop

y

FTIR


ationof

arom

aticmoietyp

resent

inlignin

characteris

ticband

sofaromaticrin

gsm

etho

xyand

aliphatic

sidec

hains

decrease

inTO

Cvalues

over

time

decrease


increase

catalystdo

sageB

utaft

ercatalystthreshold

valueisa


ausesa

decrease

indegradationrates

FTIR

peaksa

reshifted

towards

lower

molecular

weightregionaft

erph

otocatalysis

Tonu

cci

etal[33]

Testof

catalytic

syste

mstoob

tain

fractio

nswith

redu

ceddegreeso

fpo

lymerization

comparis

onof

thermalandph

otochemical

reactio

ns

1 HNMR

gasc

hrom

atograph

y-mass

spectro

scop

y(G

C-MS)

POMsa

relessselectivew

henused

asph

otocatalystsandno

appreciableb

leaching

ofthes

olutionwas

seen

whenPO

Mwas

used

asthermalcatalyst

deriv

edchem

icalsfrom

experim

entvanillin

hydroxylmetho

xy-acetoph

enon

econiferylalcoh

olcon


lform

icacidacetic

acidand

sometim

essm

allamou

ntso

fC-2

andC-

3alcoho

ls

Miyatae

tal[24]

Exam

inationof

cellwall

structureo

flignin(w

oodflo

ur)

before

andaft

erph

otocatalysis

GC-

MSscanning

electronmicroscop

y(SEM

)1 H

NMR



nedto

thes

urface

oflignin

deriv

edchem

icalse

xperim

entvanillin

Shende

etal[17]Testof

combinedactio

nof

bio-

andph

otocatalyticsyste

ms

UV-Visspectroscop

yGC-

MSX-

ray

dispersiv

eenergyspectro

scop

yandX-

ray

diffractio

nanalysis(EDX

XRD)SE

M

Detectio

nof

follo

wingchem


ethyl-2

-metho

xyph

enol

metho

xyph

enyloxim

eguaiacolsuccinica


vanillin


Table3Con

tinued

Reference

Parameter

studied

Analytic

sRe

sult

Tian

etal[52]

andPanetal

[53]

Testof

combinedactio

nof

electro-and

photocatalytic

syste

ms

UV-Visspectroscop

yFT

IRSEM

X-ray

(EDX)

highperfo

rmance

liquid

chromatograph

y(H

PLC)

COD

Detectio

nof

thefollowingchem

icalscarbon

ylfunctio

nalityvanillin

andvanillica

cid

Awun

gacha

Lekeleface

tal

[54][55]

Com

paris

onof

degradationrates

bydifferent

catalyst

HPL

Cflu

orescencea

ndUV-Vis

spectro

scop

ySE

MT

OC


rdegradatio

nof

thea

liphatic

moietycomparedto

the

arom

aticmoietyof

ligninsulfonateob

tained

from

paperw

astewaterPeaks

observed

durin

gHPL

Canalysis

Someo

fthe

peaksp

rodu

cedaft

erph

otocatalysishad

fluorescences

ignals

Thissuggeststhep

rodu

ctionof

newsubstances

andflu

orop

hores

Coatin

gsprod

uced

throug

hSol-G

elprocedures

arestablea

ndcanbe

used

manytim

es



2as





2




2possesses










2to glass






2gel or TiO

2particles






2





(10 gL TiO2)











2


2-P25-SiO

2catalyst with Pt













2









2or PtTiO

2




2


HO2

∙999445999468 H+ + ∙O

2


See [76]∙O2



2



2





2














200 220 240 260 280 300 320 340 360

00

05

10

15

20

25

Abso

rban

ce

Wavelength (nm)0min

30min

60min

120min

180min

300min

360min

420min

1200min



2-P25-SiO

2)

[54]






2-



2O and NH

3 Total organic



2and H





2-P25-SiO





0 200 400 600 800 1000 12000

50

100

150

200

250

Diss

olve

d ca

rbon

(ppm

)

t (min)

TiO2-P25-SiO2


ZnO + TiO2-P25-SiO2

No coating UV light


2-P25-SiO

2+Pt TiO

2-P25-SiO

2


2-P25-SiO

2) [54]




























2O2) up to at




2O2














Acknowledgments


References
























































A vol 154 no 2-3 pp 211ndash218 2003
















2as














2aqueous suspen-










2










































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of



Adlerol


Enzyme1

23

4

4

1

2

3

5

5

6

6

Guaiacol

Veratraldehyde

Ketone

O

OO

O

O O

O

O

O

HO

HOHO

HO

OCH3

OCH3

OCH3

OCH3

OCH3

OCH3

120572120573

120574

minusH+

∙+

∙

∙+


O2

120572 120573

120574

HOHOHO

OCH3

OCH3OCH3

OCH3 OCH3

OCH3

OCH3

120572120572

120573 120573

120573

120574 120574

HO

HO

120574

OCH3

120573

HO

HO

120574

HO

OCH3

OCH3

OCH3

120572120573

120574







rutile TiO2[49] TiO


a few


Table2Summaryof

startingcond

ition

sfor

thep

hotocatalytic

degradationof

lignin

Reference

Lign

insource

Catalyst

Reactio

ncond

ition

s

MacHadoetal[42]

Peroxyform

icacid

lignins

from

eucalyptus

grandisw

ood(EL1)

EL1+

sodium

borohydride

TiO

2andH

2O2

Lign

inconcentration

025

mgmL119879=25∘C

pH11U

VVisradiatio

n120582gt300nm

40

0Wmercury

lampcylin

dricalPy

rexglassreactorcon

stanto

xygenbu

bblin

g

Ksibietal[47]

Water

solubleligninob

tained

from

blackliq

uor

TiO

2-P2

5(D

egussa)

Lign

inconcentration

90mgL119879=20∘C


pyrex

reactoro

pento

airPh

ilips

HPK

125W

lamp

Kansaletal[48]

Lign

infro

mwheatstr

awkraft

digestion

TiO

2-P2

5(D

egussa)a

ndZn

O

Lign

inconcentration

10ndash100

mgLin

100m

LZn

Ocatalystdo

se(05ndash20gL)pH

ofthes


mination

oxidantcon

centratio

n306times10minus6M


slurrypo


hypo

chlorite

solutio

n(4availableC

l 2)

Dahm

andLu

cia[

49]

Whitewater

from

indu

strialprocess

water

thatexits

inpaperm

achines

FischerS

cientifi

crutile

TiO

2

Lign

inconcentration

40mgLin

500m


42∘C

Rayonet

photochemicalcham

ber16

VWR8-W

blacklightpho

spho

r(350-nm

)lam

ps

constant

oxygen

bubb

lingpo

wer

ofillum

ination

128to

64Wlight

intensity

223ndash44

5mWcm

3

Portjanskajaand

Preis[50]

Lign

inpurchased

from

Aldric

hTiO

2P2

5-N(D

egussa)

Lign

inconcentration

100m

gLpH


open

toair

PhillipsT


inescent

mercury

UV-lampUV-radiation

120582gt360nm

pow

erdensity

ofirr

adiatio

n=07m

Wcm

2 visib

lelight

source

Tanaka

etal[51]

Lign

infro

mconiferous

woo

dTiO

2(TiO

2mdashTP

-2of

Fujititan)

Lign

inconcentration

0003to

003U


cylindrical

reactio

nvessel

Tonu

ccietal[33]

Ca2+andNH4

+ligninderiv

atives

TiO

2as

Degussa

P25

+po

lyoxom

etalates

(POM)H

2O2

Openqu

artztubes(20

mL)


1atm

multirayso

ften

UVlamps

of15W

power

eachU


Miyatae

tal[24]

Piceag

lehn

iiwoo

dflo

urTiO

2po

lyethylene

oxide(PE

O)

Reactorop

enpetrid

ish119879=30∘C119905=48h40

0Wmercury

lamp

Shende

etal[17]

Kraft

lignin

TiO

2-Zn

O-ZrO

2Lign

inconcentration

1mgmLin

10mL250W

Xeno

nlampandAM

15Glamp

filterpo

wer

density

ofirr

adiatio

n100m

Wcm

2 solarlam

psim

ulator

Tian

etal[52]

andPanetal[53]

Kraft

ligninfro

mblackliq

uor

Ta2O

5-IrO

2andPb

O2thin

film

TiO

2nano

tubePbO

2

Lign

inconcentration

30(w


119905=10minpow

erdensity

ofirr

adiatio

n20

mWcm

2 blue

waveT

M50

ASUVspot

lampEG

ampG2273

potentiosta

tgalvano


2NTPb

O2ele

ctrode

asworking

electrode

andPt

coilas

outere

lectrode

andAgAgC

lasreference

electrode

Awun

gachaL

ekele

fac

etal[54][55]

Lign

insulfo

natefro

mpaperw

aste

water

TiO

2as

Degussa

P25

TiO

2fro

msol-g

elprocesso

fTiOSO

4TT

IP

Lign

inconcentration

500m

gLin

200m

LOsram

Planon

light

sourceirradiance

30ndash4

0Wm


20nm

119905=20hreactoro

pento

air

recirculationsyste

mflow

rate225mLmin



dsand

results

from

different

workgrou

ps

Reference

Parameter

studied

Analytic

sRe

sult

MacHado

etal[42]

Roleof

hydroxylradicals

irradiatio

nof

ligninin

the

absencea

ndpresence

ofph

otocatalystT

iO2andH

2O2

Ultraviolet-v


scop

yionizatio

nabsorptio

nspectro

scop

y(IA

S)

sizee

xclusio

nchromatograph

y(SEC

)

Asharpdecrease

inthep

heno

liccontento

bservedforreactions

involvingdirect

photolysis

SEC

areductio

nof

almost50

inthea

verage

molecular

weighto

fligninequalto

14kD

after

90min

ofirr

adiatio

n

Ksibietal[47]

Irradiationof

ligninin

the

absencea

ndpresence

ofph

otocatalystT

iO2-P2

5

UV-Visspectroscop

y13C-

nucle

armagnetic

resonance(NMR)

solid

state

totalion

gasc

hrom

atograph

y(TIC)

indu

ctioncoup

lingplasma(

ICP)

chem

icaloxygen

demand(C

OD)


TiO

2catalystaft

er420m

inreactiontim


uctsshow

edvanillin

vanillica

cidpalm

itica

cid

biph

enylstructuresand

345-trim

etho

xybenzaldehyde

presence

ofmagnesiu

mandcalcium

ions

CODremovalishigh

erforthe


ofligninsolutio

n

Kansaletal[48]

Catalystdo

sepHoxidant

concentration

initialsubstrate

concentration

ZnOcatalystin

slurryandim

mob

ilizedmod

e

UV-Visspectroscop

yCO

D

Optim

umcatalystdo

seis1gL

optim

umoxidantcon

centratio

n2times10minus6M

graduald

ecreaseo

fabsorptionpeak

indicatin

gdecompo

sitionof

organics

CODremovalishigh

erforthe


ofligninsolutio

n

Dahm

and

Lucia[

49]

Catalystdo

seillu

mination

intensity

UV-Visspectroscop

ytotalorganiccarbon

(TOC)

capillaryionelectro

phoresis

analysis(C

IA)

Gradu

aldecrease

inabsorptio

npeak

indicatin

gdecompo

sitionof

organics

optim

alcatalystdo

seof

10mgm

high

erillum

inationintensities

correlated

well

with

high


74disapp

earanceo

fTOC

Portjanskajaand

Preis[50]

Influ

ence

offerrou

sion

sN-dop

edcatalysteffect

sprayedcatalyston

supp

ortand

subm

ersedcatalyst

CODU

V-Visspectroscop

ybiochemical

oxygen

demand(BOD)colorim

etric

measurementat570

nm

Additio

nof

Fe2+upto

28m

gLleadsto25increase

inph

otocatalyticeffi

ciency


times

high

ereffi

ciency

than

theo

neattached

bysubm

ersio

nnegligibleeffecto

fN-dop

edcatalyst

increase

ofaldehyde

concentrationover

reactio

ntim

eneutralm

ediawas

mostb

eneficialforb

iodegradability

80of

freep

heno

lsremoved

undern

eutralcond

ition

s

Tanaka

etal[51]Ca

talystloadinglignin

concentration

illum

inationtim

e

UV-Visspectroscop

yTO

Cgel

perm

eatio

nchromatograph

y(G

PC)

1 HNMR

Fouriertransform

ationinfrared

(FTIR)

spectro

scop

y

FTIR


ationof

arom

aticmoietyp

resent

inlignin

characteris

ticband

sofaromaticrin

gsm

etho

xyand

aliphatic

sidec

hains

decrease

inTO

Cvalues

over

time

decrease


increase

catalystdo

sageB

utaft

ercatalystthreshold

valueisa


ausesa

decrease

indegradationrates

FTIR

peaksa

reshifted

towards

lower

molecular

weightregionaft

erph

otocatalysis

Tonu

cci

etal[33]

Testof

catalytic

syste

mstoob

tain

fractio

nswith

redu

ceddegreeso

fpo

lymerization

comparis

onof

thermalandph

otochemical

reactio

ns

1 HNMR

gasc

hrom

atograph

y-mass

spectro

scop

y(G

C-MS)

POMsa

relessselectivew

henused

asph

otocatalystsandno

appreciableb

leaching

ofthes

olutionwas

seen

whenPO

Mwas

used

asthermalcatalyst

deriv

edchem

icalsfrom

experim

entvanillin

hydroxylmetho

xy-acetoph

enon

econiferylalcoh

olcon


lform

icacidacetic

acidand

sometim

essm

allamou

ntso

fC-2

andC-

3alcoho

ls

Miyatae

tal[24]

Exam

inationof

cellwall

structureo

flignin(w

oodflo

ur)

before

andaft

erph

otocatalysis

GC-

MSscanning

electronmicroscop

y(SEM

)1 H

NMR



nedto

thes

urface

oflignin

deriv

edchem

icalse

xperim

entvanillin

Shende

etal[17]Testof

combinedactio

nof

bio-

andph

otocatalyticsyste

ms

UV-Visspectroscop

yGC-

MSX-

ray

dispersiv

eenergyspectro

scop

yandX-

ray

diffractio

nanalysis(EDX

XRD)SE

M

Detectio

nof

follo

wingchem


ethyl-2

-metho

xyph

enol

metho

xyph

enyloxim

eguaiacolsuccinica


vanillin


Table3Con

tinued

Reference

Parameter

studied

Analytic

sRe

sult

Tian

etal[52]

andPanetal

[53]

Testof

combinedactio

nof

electro-and

photocatalytic

syste

ms

UV-Visspectroscop

yFT

IRSEM

X-ray

(EDX)

highperfo

rmance

liquid

chromatograph

y(H

PLC)

COD

Detectio

nof

thefollowingchem

icalscarbon

ylfunctio

nalityvanillin

andvanillica

cid

Awun

gacha

Lekeleface

tal

[54][55]

Com

paris

onof

degradationrates

bydifferent

catalyst

HPL

Cflu

orescencea

ndUV-Vis

spectro

scop

ySE

MT

OC


rdegradatio

nof

thea

liphatic

moietycomparedto

the

arom

aticmoietyof

ligninsulfonateob

tained

from

paperw

astewaterPeaks

observed

durin

gHPL

Canalysis

Someo

fthe

peaksp

rodu

cedaft

erph

otocatalysishad

fluorescences

ignals

Thissuggeststhep

rodu

ctionof

newsubstances

andflu

orop

hores

Coatin

gsprod

uced

throug

hSol-G

elprocedures

arestablea

ndcanbe

used

manytim

es



2as





2




2possesses










2to glass






2gel or TiO

2particles






2





(10 gL TiO2)











2


2-P25-SiO

2catalyst with Pt













2









2or PtTiO

2




2


HO2

∙999445999468 H+ + ∙O

2


See [76]∙O2



2



2





2














200 220 240 260 280 300 320 340 360

00

05

10

15

20

25

Abso

rban

ce

Wavelength (nm)0min

30min

60min

120min

180min

300min

360min

420min

1200min



2-P25-SiO

2)

[54]






2-



2O and NH

3 Total organic



2and H





2-P25-SiO





0 200 400 600 800 1000 12000

50

100

150

200

250

Diss

olve

d ca

rbon

(ppm

)

t (min)

TiO2-P25-SiO2


ZnO + TiO2-P25-SiO2

No coating UV light


2-P25-SiO

2+Pt TiO

2-P25-SiO

2


2-P25-SiO

2) [54]




























2O2) up to at




2O2














Acknowledgments


References
























































A vol 154 no 2-3 pp 211ndash218 2003
















2as














2aqueous suspen-










2










































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


Table2Summaryof

startingcond

ition

sfor

thep

hotocatalytic

degradationof

lignin

Reference

Lign

insource

Catalyst

Reactio

ncond

ition

s

MacHadoetal[42]

Peroxyform

icacid

lignins

from

eucalyptus

grandisw

ood(EL1)

EL1+

sodium

borohydride

TiO

2andH

2O2

Lign

inconcentration

025

mgmL119879=25∘C

pH11U

VVisradiatio

n120582gt300nm

40

0Wmercury

lampcylin

dricalPy

rexglassreactorcon

stanto

xygenbu

bblin

g

Ksibietal[47]

Water

solubleligninob

tained

from

blackliq

uor

TiO

2-P2

5(D

egussa)

Lign

inconcentration

90mgL119879=20∘C


pyrex

reactoro

pento

airPh

ilips

HPK

125W

lamp

Kansaletal[48]

Lign

infro

mwheatstr

awkraft

digestion

TiO

2-P2

5(D

egussa)a

ndZn

O

Lign

inconcentration

10ndash100

mgLin

100m

LZn

Ocatalystdo

se(05ndash20gL)pH

ofthes


mination

oxidantcon

centratio

n306times10minus6M


slurrypo


hypo

chlorite

solutio

n(4availableC

l 2)

Dahm

andLu

cia[

49]

Whitewater

from

indu

strialprocess

water

thatexits

inpaperm

achines

FischerS

cientifi

crutile

TiO

2

Lign

inconcentration

40mgLin

500m


42∘C

Rayonet

photochemicalcham

ber16

VWR8-W

blacklightpho

spho

r(350-nm

)lam

ps

constant

oxygen

bubb

lingpo

wer

ofillum

ination

128to

64Wlight

intensity

223ndash44

5mWcm

3

Portjanskajaand

Preis[50]

Lign

inpurchased

from

Aldric

hTiO

2P2

5-N(D

egussa)

Lign

inconcentration

100m

gLpH


open

toair

PhillipsT


inescent

mercury

UV-lampUV-radiation

120582gt360nm

pow

erdensity

ofirr

adiatio

n=07m

Wcm

2 visib

lelight

source

Tanaka

etal[51]

Lign

infro

mconiferous

woo

dTiO

2(TiO

2mdashTP

-2of

Fujititan)

Lign

inconcentration

0003to

003U


cylindrical

reactio

nvessel

Tonu

ccietal[33]

Ca2+andNH4

+ligninderiv

atives

TiO

2as

Degussa

P25

+po

lyoxom

etalates

(POM)H

2O2

Openqu

artztubes(20

mL)


1atm

multirayso

ften

UVlamps

of15W

power

eachU


Miyatae

tal[24]

Piceag

lehn

iiwoo

dflo

urTiO

2po

lyethylene

oxide(PE

O)

Reactorop

enpetrid

ish119879=30∘C119905=48h40

0Wmercury

lamp

Shende

etal[17]

Kraft

lignin

TiO

2-Zn

O-ZrO

2Lign

inconcentration

1mgmLin

10mL250W

Xeno

nlampandAM

15Glamp

filterpo

wer

density

ofirr

adiatio

n100m

Wcm

2 solarlam

psim

ulator

Tian

etal[52]

andPanetal[53]

Kraft

ligninfro

mblackliq

uor

Ta2O

5-IrO

2andPb

O2thin

film

TiO

2nano

tubePbO

2

Lign

inconcentration

30(w


119905=10minpow

erdensity

ofirr

adiatio

n20

mWcm

2 blue

waveT

M50

ASUVspot

lampEG

ampG2273

potentiosta

tgalvano


2NTPb

O2ele

ctrode

asworking

electrode

andPt

coilas

outere

lectrode

andAgAgC

lasreference

electrode

Awun

gachaL

ekele

fac

etal[54][55]

Lign

insulfo

natefro

mpaperw

aste

water

TiO

2as

Degussa

P25

TiO

2fro

msol-g

elprocesso

fTiOSO

4TT

IP

Lign

inconcentration

500m

gLin

200m

LOsram

Planon

light

sourceirradiance

30ndash4

0Wm


20nm

119905=20hreactoro

pento

air

recirculationsyste

mflow

rate225mLmin



dsand

results

from

different

workgrou

ps

Reference

Parameter

studied

Analytic

sRe

sult

MacHado

etal[42]

Roleof

hydroxylradicals

irradiatio

nof

ligninin

the

absencea

ndpresence

ofph

otocatalystT

iO2andH

2O2

Ultraviolet-v


scop

yionizatio

nabsorptio

nspectro

scop

y(IA

S)

sizee

xclusio

nchromatograph

y(SEC

)

Asharpdecrease

inthep

heno

liccontento

bservedforreactions

involvingdirect

photolysis

SEC

areductio

nof

almost50

inthea

verage

molecular

weighto

fligninequalto

14kD

after

90min

ofirr

adiatio

n

Ksibietal[47]

Irradiationof

ligninin

the

absencea

ndpresence

ofph

otocatalystT

iO2-P2

5

UV-Visspectroscop

y13C-

nucle

armagnetic

resonance(NMR)

solid

state

totalion

gasc

hrom

atograph

y(TIC)

indu

ctioncoup

lingplasma(

ICP)

chem

icaloxygen

demand(C

OD)


TiO

2catalystaft

er420m

inreactiontim


uctsshow

edvanillin

vanillica

cidpalm

itica

cid

biph

enylstructuresand

345-trim

etho

xybenzaldehyde

presence

ofmagnesiu

mandcalcium

ions

CODremovalishigh

erforthe


ofligninsolutio

n

Kansaletal[48]

Catalystdo

sepHoxidant

concentration

initialsubstrate

concentration

ZnOcatalystin

slurryandim

mob

ilizedmod

e

UV-Visspectroscop

yCO

D

Optim

umcatalystdo

seis1gL

optim

umoxidantcon

centratio

n2times10minus6M

graduald

ecreaseo

fabsorptionpeak

indicatin

gdecompo

sitionof

organics

CODremovalishigh

erforthe


ofligninsolutio

n

Dahm

and

Lucia[

49]

Catalystdo

seillu

mination

intensity

UV-Visspectroscop

ytotalorganiccarbon

(TOC)

capillaryionelectro

phoresis

analysis(C

IA)

Gradu

aldecrease

inabsorptio

npeak

indicatin

gdecompo

sitionof

organics

optim

alcatalystdo

seof

10mgm

high

erillum

inationintensities

correlated

well

with

high


74disapp

earanceo

fTOC

Portjanskajaand

Preis[50]

Influ

ence

offerrou

sion

sN-dop

edcatalysteffect

sprayedcatalyston

supp

ortand

subm

ersedcatalyst

CODU

V-Visspectroscop

ybiochemical

oxygen

demand(BOD)colorim

etric

measurementat570

nm

Additio

nof

Fe2+upto

28m

gLleadsto25increase

inph

otocatalyticeffi

ciency


times

high

ereffi

ciency

than

theo

neattached

bysubm

ersio

nnegligibleeffecto

fN-dop

edcatalyst

increase

ofaldehyde

concentrationover

reactio

ntim

eneutralm

ediawas

mostb

eneficialforb

iodegradability

80of

freep

heno

lsremoved

undern

eutralcond

ition

s

Tanaka

etal[51]Ca

talystloadinglignin

concentration

illum

inationtim

e

UV-Visspectroscop

yTO

Cgel

perm

eatio

nchromatograph

y(G

PC)

1 HNMR

Fouriertransform

ationinfrared

(FTIR)

spectro

scop

y

FTIR


ationof

arom

aticmoietyp

resent

inlignin

characteris

ticband

sofaromaticrin

gsm

etho

xyand

aliphatic

sidec

hains

decrease

inTO

Cvalues

over

time

decrease


increase

catalystdo

sageB

utaft

ercatalystthreshold

valueisa


ausesa

decrease

indegradationrates

FTIR

peaksa

reshifted

towards

lower

molecular

weightregionaft

erph

otocatalysis

Tonu

cci

etal[33]

Testof

catalytic

syste

mstoob

tain

fractio

nswith

redu

ceddegreeso

fpo

lymerization

comparis

onof

thermalandph

otochemical

reactio

ns

1 HNMR

gasc

hrom

atograph

y-mass

spectro

scop

y(G

C-MS)

POMsa

relessselectivew

henused

asph

otocatalystsandno

appreciableb

leaching

ofthes

olutionwas

seen

whenPO

Mwas

used

asthermalcatalyst

deriv

edchem

icalsfrom

experim

entvanillin

hydroxylmetho

xy-acetoph

enon

econiferylalcoh

olcon


lform

icacidacetic

acidand

sometim

essm

allamou

ntso

fC-2

andC-

3alcoho

ls

Miyatae

tal[24]

Exam

inationof

cellwall

structureo

flignin(w

oodflo

ur)

before

andaft

erph

otocatalysis

GC-

MSscanning

electronmicroscop

y(SEM

)1 H

NMR



nedto

thes

urface

oflignin

deriv

edchem

icalse

xperim

entvanillin

Shende

etal[17]Testof

combinedactio

nof

bio-

andph

otocatalyticsyste

ms

UV-Visspectroscop

yGC-

MSX-

ray

dispersiv

eenergyspectro

scop

yandX-

ray

diffractio

nanalysis(EDX

XRD)SE

M

Detectio

nof

follo

wingchem


ethyl-2

-metho

xyph

enol

metho

xyph

enyloxim

eguaiacolsuccinica


vanillin


Table3Con

tinued

Reference

Parameter

studied

Analytic

sRe

sult

Tian

etal[52]

andPanetal

[53]

Testof

combinedactio

nof

electro-and

photocatalytic

syste

ms

UV-Visspectroscop

yFT

IRSEM

X-ray

(EDX)

highperfo

rmance

liquid

chromatograph

y(H

PLC)

COD

Detectio

nof

thefollowingchem

icalscarbon

ylfunctio

nalityvanillin

andvanillica

cid

Awun

gacha

Lekeleface

tal

[54][55]

Com

paris

onof

degradationrates

bydifferent

catalyst

HPL

Cflu

orescencea

ndUV-Vis

spectro

scop

ySE

MT

OC


rdegradatio

nof

thea

liphatic

moietycomparedto

the

arom

aticmoietyof

ligninsulfonateob

tained

from

paperw

astewaterPeaks

observed

durin

gHPL

Canalysis

Someo

fthe

peaksp

rodu

cedaft

erph

otocatalysishad

fluorescences

ignals

Thissuggeststhep

rodu

ctionof

newsubstances

andflu

orop

hores

Coatin

gsprod

uced

throug

hSol-G

elprocedures

arestablea

ndcanbe

used

manytim

es



2as





2




2possesses










2to glass






2gel or TiO

2particles






2





(10 gL TiO2)











2


2-P25-SiO

2catalyst with Pt













2









2or PtTiO

2




2


HO2

∙999445999468 H+ + ∙O

2


See [76]∙O2



2



2





2














200 220 240 260 280 300 320 340 360

00

05

10

15

20

25

Abso

rban

ce

Wavelength (nm)0min

30min

60min

120min

180min

300min

360min

420min

1200min



2-P25-SiO

2)

[54]






2-



2O and NH

3 Total organic



2and H





2-P25-SiO





0 200 400 600 800 1000 12000

50

100

150

200

250

Diss

olve

d ca

rbon

(ppm

)

t (min)

TiO2-P25-SiO2


ZnO + TiO2-P25-SiO2

No coating UV light


2-P25-SiO

2+Pt TiO

2-P25-SiO

2


2-P25-SiO

2) [54]




























2O2) up to at




2O2














Acknowledgments


References
























































A vol 154 no 2-3 pp 211ndash218 2003
















2as














2aqueous suspen-










2










































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of



dsand

results

from

different

workgrou

ps

Reference

Parameter

studied

Analytic

sRe

sult

MacHado

etal[42]

Roleof

hydroxylradicals

irradiatio

nof

ligninin

the

absencea

ndpresence

ofph

otocatalystT

iO2andH

2O2

Ultraviolet-v


scop

yionizatio

nabsorptio

nspectro

scop

y(IA

S)

sizee

xclusio

nchromatograph

y(SEC

)

Asharpdecrease

inthep

heno

liccontento

bservedforreactions

involvingdirect

photolysis

SEC

areductio

nof

almost50

inthea

verage

molecular

weighto

fligninequalto

14kD

after

90min

ofirr

adiatio

n

Ksibietal[47]

Irradiationof

ligninin

the

absencea

ndpresence

ofph

otocatalystT

iO2-P2

5

UV-Visspectroscop

y13C-

nucle

armagnetic

resonance(NMR)

solid

state

totalion

gasc

hrom

atograph

y(TIC)

indu

ctioncoup

lingplasma(

ICP)

chem

icaloxygen

demand(C

OD)


TiO

2catalystaft

er420m

inreactiontim


uctsshow

edvanillin

vanillica

cidpalm

itica

cid

biph

enylstructuresand

345-trim

etho

xybenzaldehyde

presence

ofmagnesiu

mandcalcium

ions

CODremovalishigh

erforthe


ofligninsolutio

n

Kansaletal[48]

Catalystdo

sepHoxidant

concentration

initialsubstrate

concentration

ZnOcatalystin

slurryandim

mob

ilizedmod

e

UV-Visspectroscop

yCO

D

Optim

umcatalystdo

seis1gL

optim

umoxidantcon

centratio

n2times10minus6M

graduald

ecreaseo

fabsorptionpeak

indicatin

gdecompo

sitionof

organics

CODremovalishigh

erforthe


ofligninsolutio

n

Dahm

and

Lucia[

49]

Catalystdo

seillu

mination

intensity

UV-Visspectroscop

ytotalorganiccarbon

(TOC)

capillaryionelectro

phoresis

analysis(C

IA)

Gradu

aldecrease

inabsorptio

npeak

indicatin

gdecompo

sitionof

organics

optim

alcatalystdo

seof

10mgm

high

erillum

inationintensities

correlated

well

with

high


74disapp

earanceo

fTOC

Portjanskajaand

Preis[50]

Influ

ence

offerrou

sion

sN-dop

edcatalysteffect

sprayedcatalyston

supp

ortand

subm

ersedcatalyst

CODU

V-Visspectroscop

ybiochemical

oxygen

demand(BOD)colorim

etric

measurementat570

nm

Additio

nof

Fe2+upto

28m

gLleadsto25increase

inph

otocatalyticeffi

ciency


times

high

ereffi

ciency

than

theo

neattached

bysubm

ersio

nnegligibleeffecto

fN-dop

edcatalyst

increase

ofaldehyde

concentrationover

reactio

ntim

eneutralm

ediawas

mostb

eneficialforb

iodegradability

80of

freep

heno

lsremoved

undern

eutralcond

ition

s

Tanaka

etal[51]Ca

talystloadinglignin

concentration

illum

inationtim

e

UV-Visspectroscop

yTO

Cgel

perm

eatio

nchromatograph

y(G

PC)

1 HNMR

Fouriertransform

ationinfrared

(FTIR)

spectro

scop

y

FTIR


ationof

arom

aticmoietyp

resent

inlignin

characteris

ticband

sofaromaticrin

gsm

etho

xyand

aliphatic

sidec

hains

decrease

inTO

Cvalues

over

time

decrease


increase

catalystdo

sageB

utaft

ercatalystthreshold

valueisa


ausesa

decrease

indegradationrates

FTIR

peaksa

reshifted

towards

lower

molecular

weightregionaft

erph

otocatalysis

Tonu

cci

etal[33]

Testof

catalytic

syste

mstoob

tain

fractio

nswith

redu

ceddegreeso

fpo

lymerization

comparis

onof

thermalandph

otochemical

reactio

ns

1 HNMR

gasc

hrom

atograph

y-mass

spectro

scop

y(G

C-MS)

POMsa

relessselectivew

henused

asph

otocatalystsandno

appreciableb

leaching

ofthes

olutionwas

seen

whenPO

Mwas

used

asthermalcatalyst

deriv

edchem

icalsfrom

experim

entvanillin

hydroxylmetho

xy-acetoph

enon

econiferylalcoh

olcon


lform

icacidacetic

acidand

sometim

essm

allamou

ntso

fC-2

andC-

3alcoho

ls

Miyatae

tal[24]

Exam

inationof

cellwall

structureo

flignin(w

oodflo

ur)

before

andaft

erph

otocatalysis

GC-

MSscanning

electronmicroscop

y(SEM

)1 H

NMR



nedto

thes

urface

oflignin

deriv

edchem

icalse

xperim

entvanillin

Shende

etal[17]Testof

combinedactio

nof

bio-

andph

otocatalyticsyste

ms

UV-Visspectroscop

yGC-

MSX-

ray

dispersiv

eenergyspectro

scop

yandX-

ray

diffractio

nanalysis(EDX

XRD)SE

M

Detectio

nof

follo

wingchem


ethyl-2

-metho

xyph

enol

metho

xyph

enyloxim

eguaiacolsuccinica


vanillin


Table3Con

tinued

Reference

Parameter

studied

Analytic

sRe

sult

Tian

etal[52]

andPanetal

[53]

Testof

combinedactio

nof

electro-and

photocatalytic

syste

ms

UV-Visspectroscop

yFT

IRSEM

X-ray

(EDX)

highperfo

rmance

liquid

chromatograph

y(H

PLC)

COD

Detectio

nof

thefollowingchem

icalscarbon

ylfunctio

nalityvanillin

andvanillica

cid

Awun

gacha

Lekeleface

tal

[54][55]

Com

paris

onof

degradationrates

bydifferent

catalyst

HPL

Cflu

orescencea

ndUV-Vis

spectro

scop

ySE

MT

OC


rdegradatio

nof

thea

liphatic

moietycomparedto

the

arom

aticmoietyof

ligninsulfonateob

tained

from

paperw

astewaterPeaks

observed

durin

gHPL

Canalysis

Someo

fthe

peaksp

rodu

cedaft

erph

otocatalysishad

fluorescences

ignals

Thissuggeststhep

rodu

ctionof

newsubstances

andflu

orop

hores

Coatin

gsprod

uced

throug

hSol-G

elprocedures

arestablea

ndcanbe

used

manytim

es



2as





2




2possesses










2to glass






2gel or TiO

2particles






2





(10 gL TiO2)











2


2-P25-SiO

2catalyst with Pt













2









2or PtTiO

2




2


HO2

∙999445999468 H+ + ∙O

2


See [76]∙O2



2



2





2














200 220 240 260 280 300 320 340 360

00

05

10

15

20

25

Abso

rban

ce

Wavelength (nm)0min

30min

60min

120min

180min

300min

360min

420min

1200min



2-P25-SiO

2)

[54]






2-



2O and NH

3 Total organic



2and H





2-P25-SiO





0 200 400 600 800 1000 12000

50

100

150

200

250

Diss

olve

d ca

rbon

(ppm

)

t (min)

TiO2-P25-SiO2


ZnO + TiO2-P25-SiO2

No coating UV light


2-P25-SiO

2+Pt TiO

2-P25-SiO

2


2-P25-SiO

2) [54]




























2O2) up to at




2O2














Acknowledgments


References
























































A vol 154 no 2-3 pp 211ndash218 2003
















2as














2aqueous suspen-










2










































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


Table3Con

tinued

Reference

Parameter

studied

Analytic

sRe

sult

Tian

etal[52]

andPanetal

[53]

Testof

combinedactio

nof

electro-and

photocatalytic

syste

ms

UV-Visspectroscop

yFT

IRSEM

X-ray

(EDX)

highperfo

rmance

liquid

chromatograph

y(H

PLC)

COD

Detectio

nof

thefollowingchem

icalscarbon

ylfunctio

nalityvanillin

andvanillica

cid

Awun

gacha

Lekeleface

tal

[54][55]

Com

paris

onof

degradationrates

bydifferent

catalyst

HPL

Cflu

orescencea

ndUV-Vis

spectro

scop

ySE

MT

OC


rdegradatio

nof

thea

liphatic

moietycomparedto

the

arom

aticmoietyof

ligninsulfonateob

tained

from

paperw

astewaterPeaks

observed

durin

gHPL

Canalysis

Someo

fthe

peaksp

rodu

cedaft

erph

otocatalysishad

fluorescences

ignals

Thissuggeststhep

rodu

ctionof

newsubstances

andflu

orop

hores

Coatin

gsprod

uced

throug

hSol-G

elprocedures

arestablea

ndcanbe

used

manytim

es



2as





2




2possesses










2to glass






2gel or TiO

2particles






2





(10 gL TiO2)











2


2-P25-SiO

2catalyst with Pt













2









2or PtTiO

2




2


HO2

∙999445999468 H+ + ∙O

2


See [76]∙O2



2



2





2














200 220 240 260 280 300 320 340 360

00

05

10

15

20

25

Abso

rban

ce

Wavelength (nm)0min

30min

60min

120min

180min

300min

360min

420min

1200min



2-P25-SiO

2)

[54]






2-



2O and NH

3 Total organic



2and H





2-P25-SiO





0 200 400 600 800 1000 12000

50

100

150

200

250

Diss

olve

d ca

rbon

(ppm

)

t (min)

TiO2-P25-SiO2


ZnO + TiO2-P25-SiO2

No coating UV light


2-P25-SiO

2+Pt TiO

2-P25-SiO

2


2-P25-SiO

2) [54]




























2O2) up to at




2O2














Acknowledgments


References
























































A vol 154 no 2-3 pp 211ndash218 2003
















2as














2aqueous suspen-










2










































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of



2as





2




2possesses










2to glass






2gel or TiO

2particles






2





(10 gL TiO2)











2


2-P25-SiO

2catalyst with Pt













2









2or PtTiO

2




2


HO2

∙999445999468 H+ + ∙O

2


See [76]∙O2



2



2





2














200 220 240 260 280 300 320 340 360

00

05

10

15

20

25

Abso

rban

ce

Wavelength (nm)0min

30min

60min

120min

180min

300min

360min

420min

1200min



2-P25-SiO

2)

[54]






2-



2O and NH

3 Total organic



2and H





2-P25-SiO





0 200 400 600 800 1000 12000

50

100

150

200

250

Diss

olve

d ca

rbon

(ppm

)

t (min)

TiO2-P25-SiO2


ZnO + TiO2-P25-SiO2

No coating UV light


2-P25-SiO

2+Pt TiO

2-P25-SiO

2


2-P25-SiO

2) [54]




























2O2) up to at




2O2














Acknowledgments


References
























































A vol 154 no 2-3 pp 211ndash218 2003
















2as














2aqueous suspen-










2










































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of





2









2or PtTiO

2




2


HO2

∙999445999468 H+ + ∙O

2


See [76]∙O2



2



2





2














200 220 240 260 280 300 320 340 360

00

05

10

15

20

25

Abso

rban

ce

Wavelength (nm)0min

30min

60min

120min

180min

300min

360min

420min

1200min



2-P25-SiO

2)

[54]






2-



2O and NH

3 Total organic



2and H





2-P25-SiO





0 200 400 600 800 1000 12000

50

100

150

200

250

Diss

olve

d ca

rbon

(ppm

)

t (min)

TiO2-P25-SiO2


ZnO + TiO2-P25-SiO2

No coating UV light


2-P25-SiO

2+Pt TiO

2-P25-SiO

2


2-P25-SiO

2) [54]




























2O2) up to at




2O2














Acknowledgments


References
























































A vol 154 no 2-3 pp 211ndash218 2003
















2as














2aqueous suspen-










2










































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of











200 220 240 260 280 300 320 340 360

00

05

10

15

20

25

Abso

rban

ce

Wavelength (nm)0min

30min

60min

120min

180min

300min

360min

420min

1200min



2-P25-SiO

2)

[54]






2-



2O and NH

3 Total organic



2and H





2-P25-SiO





0 200 400 600 800 1000 12000

50

100

150

200

250

Diss

olve

d ca

rbon

(ppm

)

t (min)

TiO2-P25-SiO2


ZnO + TiO2-P25-SiO2

No coating UV light


2-P25-SiO

2+Pt TiO

2-P25-SiO

2


2-P25-SiO

2) [54]




























2O2) up to at




2O2














Acknowledgments


References
























































A vol 154 no 2-3 pp 211ndash218 2003
















2as














2aqueous suspen-










2










































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of



2-



2O and NH

3 Total organic



2and H





2-P25-SiO





0 200 400 600 800 1000 12000

50

100

150

200

250

Diss

olve

d ca

rbon

(ppm

)

t (min)

TiO2-P25-SiO2


ZnO + TiO2-P25-SiO2

No coating UV light


2-P25-SiO

2+Pt TiO

2-P25-SiO

2


2-P25-SiO

2) [54]




























2O2) up to at




2O2














Acknowledgments


References
























































A vol 154 no 2-3 pp 211ndash218 2003
















2as














2aqueous suspen-










2










































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of

























2O2) up to at




2O2














Acknowledgments


References
























































A vol 154 no 2-3 pp 211ndash218 2003
















2as














2aqueous suspen-










2










































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of













Acknowledgments


References
























































A vol 154 no 2-3 pp 211ndash218 2003
















2as














2aqueous suspen-










2










































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of









































A vol 154 no 2-3 pp 211ndash218 2003
















2as














2aqueous suspen-










2










































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of
















2as














2aqueous suspen-










2










































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of





























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of










Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of

Date post:	17-Apr-2020
Category:	Documents
Upload:	others
View:	9 times
Download:	0 times

Review Article Photocatalytic Based Degradation Processes of...

Documents