c5ta06563A novel quasi-cubic CuFe2O4–Fe2O3 catalyst prepared at low temperature for enhanced...

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A novel quasi-cubic CuFe2O4ndash

Fe2O3 catalystprepared at low temperature for enhancedoxidation of bisphenol A via peroxymonosulfateactivationdagger

Wen-Da Ohab Zhili Dongac Zhong-Ting Hub and Teik-Thye Limab

A facile eco-friendly co-precipitation synthesis at low temperature was employed to fabricate CuFe2O4ndash

Fe2O3 for the oxidation of bisphenol A (BPA) via peroxymonosulfate (PMS) activation The formation

mechanism of CuFe2O4ndashFe2O3 at low temperature is proposed The FESEM and BET characterization

studies revealed that the CuFe2O4ndashFe2O3 catalyst has a quasi-cubic morphology and speci1047297c surface

area of 63 m2 g1 The performance of CuFe2O4ndashFe2O3 as a PMS activator was compared with those of

other catalysts and the results indicated that the performance was in the following order CuFe2O4ndash

Fe2O3 gt CuFe2O4 gt CoFe2O4 gt CuBi2O4 gt CuAl2O4 gt Fe2O3 gt MnFe2O4 A kinetic model with

mechanistic consideration of the in1047298uence of pH PMS dosage and catalyst loading was developed to

model the degradation of BPA The intrinsic rate constant (k i) was obtained from the kinetic study The

relationship between the pseudo 1047297rst-order rate constant and k i was established The trend of k i revealed

that increasing the catalyst loading decreased the BPA removal rate due to the initial preferential

production of the weaker radical (ie SO5c) for BPA degradation and Fe2+ quenching of SO4c

at higher

catalyst loading The in1047298uence of water matrix species (ie Cl NO3 HCO3

PO43 and humic acid) on

the BPA degradation rate was also investigated The CuFe2O4ndashFe2O3 catalyst exhibited excellent stability

and can be reused several times without signi1047297cant deterioration in performance

1 Introduction Advanced oxidation processes utilizing redox changes in tran-

sition metals are extensively used for the catalytic oxidation of

organic pollutants Oxidation of organic pollutants by using

sulfate radicals generated from the redox reaction between

commercially available oxidants and transition metals is being

increasingly adopted as an eco-friendly and efficient method for

removing recalcitrant pollutants from water Sulfate radicals

have a relatively high oxidation potential ( E o frac14 27 V) and they

are selective for electron transfer reactions1 A sulfate radical

has a longer half-life compared to a hydroxyl radical thus

allowing better diff usion of the generated reactive sulfate

radical for oxidation reactions in the bulk solution2 One of the

most efficient ways to generate sulfate radicals is by perox-

ymonosulfate (PMS) activation using transition metals which

can be achieved in both heterogeneous and homogeneous

reaction systems3 The heterogeneous system is advantageous

over the homogeneous system due to the ease of recovering the

catalyst for further reuse and prevention of water pollution by

the added metals The current trend of studies involves the use

of Co-based materials as PMS activators but this approach

suff ers from the dissolution of highly toxic Co ions during

treatment45 One appealing transition metal which is relatively

less toxic than Co is Cu To date the Cu-based catalysts which

have been reported include CuFe2O467 CuO8 and CuZSM59 In

most cases the catalyst preparation method involves high-temperature heat treatments environmentally harmful solvents

and other organic precursors For pragmatic applications a

facile low-energy and eco-friendly synthesis is warranted

Bisphenol A (BPA) is a xenobiotic endocrine disruptor

ubiquitously used in various manufacturing industries to

produce polycarbonate plastics and epoxy resins10 Due to its

endocrine disrupting property and widespread application

pollution due to BPA poses a potential risk to human health and

aquatic lives1112 Although a myriad of treatment methods have

been proposed in the literature such as ozonation and activated

a Nanyang Environment and Water Research Institute (NEWRI) Interdisciplinary

Graduate School (IGS) Nanyang Technological University 1 Cleantech Loop

CleanTech One Singapore 637141 Singapore E-mail cttlimntuedusg Fax +65-

6791 0676 Tel +65-6790 6933b Division of Environmental and Water Resources Engineering School of Civil and

Environmental Engineering Nanyang Technological University 50 Nanyang A venue

Singapore 639798 SingaporecSchool of Materials Science and Engineering Nanyang Technological University 50

Nanyang Avenue Singapore 639798 Singapore

dagger Electronic supplementary information (ESI) available See DOI

101039c5ta06563a

Cite this DOI 101039c5ta06563a

Received 20th August 2015

Accepted 21st September 2015

DOI 101039c5ta06563a

wwwrscorgMaterialsA

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carbon adsorption these methods require high energy

consumption or generate a secondary waste stream13

Previous investigation of the kinetics of pollutant oxidation

by using sulfate radicals in the heterogeneous system was o en

based on the pseudo rst-order kinetics with the assumption

that the oxidant (PMS) added was readily available for reac-

tion1415 Qi et al presented a second-order kinetic model to

describe the degradation of caff eine by using a Co-MCM41

catalyst16 However these kinetic models did not take intoaccount the inuence of pH PMS dosage and catalyst loading

on pollutant degradation particularly under non-ideal condi-

tions (eg non-excess PMS diff erent pH values etc) In this

regard a more robust kinetic model needs to be employed

Herein the objectives of this study are to (i) prepare and

characterize a series of catalysts encompassing CuFe2O4ndashFe2O3

ferrospinels (YFe2O4 Y frac14 Cu Co and Mn) Cu-based spinels

(CuX 2O4 X frac14 Bi and Al) and Fe2O3 (ii) investigate and compare

the performance of the as-prepared catalysts for BPA removal

via PMS activation and (iii) develop a kinetic model based on

the mechanistic consideration of various inuencing parame-

ters (ie pH PMS dosage and catalyst loading) to describe theBPA degradation The intrinsic rate constant k i was calculated

explicitly from the experimentally derived BPA degradation at

various time intervals in the kinetic modelling study and it was

compared with the pseudo rst-order rate constant (k app) to

obtain new insights into the use of heterogeneous transition

metal catalysts for pollutant removal via PMS activation

2 Experimental21 Chemicals

All the chemicals used in this study are of analytical grade The

chemicals used are as follows Cu(NO3)2$3H2O (QreC)

Co(NO3)2$6H2O (Alfa Aesar) Mn(NO3)2$4H2O (Sigma-Aldrich)

Fe(NO3)3$9H2O (Merck) Bi(NO3)3$5H2O (Alfa Aesar)

Al(NO3)3$9H2O (Sigma-Aldrich) NaOH (Alfa Aesar) HCl (Merck)

acetonitrile (Merck) citric acid (Merck) ammonia (Hach) KI

(Fisons) PMS (in the form of Oxonereg 2KHSO5$KHSO4$K2SO4

Alfa Aesar) NaCl (Qrectrade) NaNO3 (Sigma-Aldrich) humic acid

(HA Aldrich) NaHCO3 (Sigma-Aldrich) polyethylene glycol

(Sigma-Aldrich) sodium acetate (Sigma-Aldrich) bisphenol A

(Merck) and methanol (Merck) All the experiments were con-

ducted using deionized (DI) water (182 MU cm)

22 Synthesis of catalysts

The CuFe2O4ndashFe2O3 catalyst was prepared using a facile co-

precipitation method at low temperature In a typical synthesis

procedure metal precursors consisting of 5 mmol of

Cu(NO3)2$3H2O and 10 mmol of Fe(NO3)3$9H2O were dissolved

in 50 mL of DI water and the pH of the solution mixture was

adjusted to pH 10ndash11 using 6 M NaOH under rapid magnetic

stirring Then the resultant solution was heated under vigorous

stirring at 95 C for 24 h to promote hydrolysis and the

formation of the CuFe2O4ndashFe2O3 catalyst The resultant

brownish product was separated from the solution by using a

simple magnetic separation procedure and freeze-dried for 24

h Several other catalysts namely CuAl2O4 CuBi2O4 CuFe2O4

MnFe2O4 CoFe2O4 and Fe2O3 were also prepared for perfor-

mance comparison with CuFe2O4ndashFe2O3 CuAl2O4 was prepared

via a solndashgel method17 CuBi2O4 and Fe2O3 were prepared via a

low-temperature co-precipitation method13 XFe2O4 (X frac14 Mn Fe

and Co) was prepared via a solvothermal method18 The details

of the synthesis procedures for preparing ferrospinels (YFe2O4

Y frac14 Cu Co and Mn) Cu-based spinels (CuX 2O4 X frac14 Bi and Al)

and Fe2O3 are presented in the ESIdagger

23 Characterization technique

The crystallographic and mineralogical information of the as-

prepared catalysts was obtained using a X-ray diff ractometer

(Bruker AXS D8 Advance) operating at 40 kV and 40 mA with a

Cu-Ka (l frac14 15418 ˚ A) X-ray source The surface morphology and

EDX elemental distribution were studied by obtaining the

electron micrographs and elemental mappings using a eld

emission scanning electron microscope (FESEM JEOL JSM-

7600F) equipped with an energy dispersive X-ray spectrometer

(EDX Oxford Xmax80 LN2 Free) The Fourier transform infrared(FTIR) spectra were obtained using a FTIR spectrometer (Perkin

Elmer Spectrum GX) The BrunauerndashEmmett ndashTeller (BET)

specic surface area of the catalysts was calculated from the N2

adsorptionndashdesorption isotherm analysis at 77 K (Quantach-

rome Autosorb-1 Analyzer)

24 Performance evaluation

Batch experiments were conducted to investigate the perfor-

mance of the catalyst for BPA treatment via PMS activation In

a typical experimental procedure a known amount of PMS

was introduced into the reaction vessels containing 100 mL of

5 mg L1 of BPA at 25 C The pH of the solution was imme-diately adjusted to the desired pH (pH 45 70 or 95) Then a

known amount of the catalyst was added into the solution to

commence the catalytic reaction At various time intervals

2 mL aliquots were sampled from the reaction vessel to

determine the BPA concentration The collected aliquots were

ltered using a cellulose acetate membrane lter and the

catalytic reaction was quenched using methanol The BPA

concentration was then determined by using high perfor-

mance liquid chromatography (HPLC) At the end of the

reaction time the pH change of the solution at pH 45 was

insignicant while for pH 70 and 95 the nal pH was 61 and

81 respectively due to their unbuff

ered condition and theformation of acidic BPA intermediates such as organic acids13

The experimental parameters studied were the PMS dosage

(018 027 and 036 g L1) catalyst loading (005 010 and

020 g L1) and initial pH (45 70 and 95) The mole ratio of

PMS to pollutant used in this study was comparable to that of

another study19 At the end of the reaction time the total

organic carbon and Cu leaching were also determined for the

selected conditions For the TOC determination the samples

were ltered and analyzed immediately without quenching

with methanol Investigation of the changes in PMS concen-

tration over time was also conducted

J Mater Chem A This journal is copy The Royal Society of Chemistry 2015

Journal of Materials Chemistry A Paper

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25 Analytical methods

The BPA concentration was determined from the calibration

curve which was developed using a HPLC (Perkin Elmer UV

detector) operating with a reverse phase column (Hypersil

Gold) and a mobile phase consisting of 60 acetonitrile and

40 water The BPA detection wavelength was 220 nm TOC

and Cu ion measurements were conducted using a TOC

Analyzer (Shimadzu ASI-V) and ICP-OES (PerkinElmer Elmer

Optima 2000DV) respectively The point of zero charge (pHzpc)

of the catalyst was determined using the pH dri method as

described by Lopez-Ramon et al20 with slight modication

Brie y a series of 30 mL of 001 mM NaCl solutions were

prepared Then 009 g of the catalyst was added into the

solutions and the pH of the solutions was adjusted to be

between pH 3ndash12 using 1 M NaOH or 01 M HCl A er 48 h the

pH of the solutions was measured again and pHzpc which is

the point at which pH(initial) frac14 pH(nal) was determined

from the intercept of the DpH vs pH(initial) plot The PMS

concentration was quantied using the iodometric method

with the aid of a UV-Vis spectrophotometer Brie y 5 mL of

sample was mixed with 1 g of KI and agitated vigorously for 30min Then the sample mixture was analyzed using a UV-Vis

spectrophotometer at lmax frac14 353 nm and the PMS concen-

tration was determined using a pre-developed calibration

curve

3 Results and discussion31 Synthesis and characteristics of the as-prepared catalysts

The CuFe2O4ndashFe2O3 catalyst was successfully prepared by

employing an eco-friendly solvent- and surfactant-free co-

precipitation method at low temperature The low temperature

synthesis method was previously used to prepare Fe2O313 TheCuFe2O4ndashFe2O3 presents an improvement over the Fe2O3 cata-

lyst due to the presence of Cu which can lead to the synergistic

Cu and Fe coupling eff ect For performance comparison other

catalysts namely ferrospinels (YFe2O4 Y frac14 Cu Co and Mn) Cu-

based spinels (CuX 2O4 X frac14 Bi and Al) and Fe2O3 were also

prepared using various synthesis methods encompassing sol-

vothermal solndashgel hydrothermal and co-precipitation

methods Fig 1a shows the XRD patterns and FTIR spectra of all

the as-prepared catalysts The XRD peaks of the CuFe2O4ndashFe2O3

catalyst can be indexed to both the CuFe2O4 spinel and Fe2O3

phases Rietveld renement analysis shows that the CuFe2O4ndash

Fe2O3 catalyst has a compositional ratio (ww) of 2 CuFe2O4 to 3Fe2O3 (83 Fe3+ 17 Cu2+) All the solvothermally prepared

ferrospinels are of single phase except for CuFe2O4 which has

20 ww of Cu0 attributed to the use of ethylene glycol which

can act as a reducing agent21 The XRD pattern of CuBi2O4 can

be indexed to the single phase CuBi2O4 The XRD pattern of

CuAl2O4 shows that additional peaks attributed to a small

amount of CuO (10 ww by Rietveld renement analysis) are

also present In all the FTIR spectra (Fig 1b) the broad band

located at 3400 cm1 is indicative of the presence of surface

hydroxyl functional groups The surface hydroxyl groups are

partly responsible for enhancing the pollutant oxidation

rate

2223

The distinctive peak at 600 cm

1

in all the FTIR spectra was attributed to the characteristic MendashO bond

The FESEM micrograph (Fig 2d) of the CuFe2O4ndashFe2O3

catalyst consists of a quasi-cubic morphology with a mean size

of 100ndash200 nm The EDX elemental mapping (Fig 2e) shows

that Cu and Fe were homogeneously distributed on the surface

at a ratio of 1 Cu to 55 Fe which is close to the theoretical ratio

of 1 Cu to5 Fe This indicates the coexistence of CuFe2O4 and

Fe2O3 phases in the cubic nanostructure The BET result indi-

cates that it has a specic surface area of 63 m2 g 1 As the

synthesis of spinel CuFe2O4 was carried out at a relatively lower

synthesis temperature than those reported in the literature the

elapsed-aging time was crucial for obtaining the desired

morphology and crystallographic phase6724 To obtain insightsinto the formation of CuFe2O4ndashFe2O3 time-dependent FESEM

micrographs and XRD patterns of CuFe2O4ndashFe2O3 were

obtained (Fig 2) Although the catalysts prepared at t frac14 3 and 5

h have magnetic properties the FESEM micrograph and XRD

pattern indicate that they consist of relatively amorphous

nanoparticles With further increase in the reaction time the

crystallinity of the nanoparticles improved and the nano-

particles began to self-assemble forming a quasi-cubic structure

via Ostwald ripening as indicated in Fig 2c The increase in the

synthesis time for the low temperature synthesis has also been

reported to increase the crystallinity of a material25 The

proposed schematic illustration of the CuFe2O4ndash

Fe2O3 forma-tion mechanism is shown in Fig 3

All the other catalysts were of quasi-spherical morphologies

(Fig S1andashedagger) except for CuAl2O4 which consists of irregular

microparticles (Fig S1f dagger) The solvothermal synthesis protocol

involving the use of surfactants resulted in materials with a

relatively higher specic surface area than the low temperature

co-precipitation method due to a signicant reduction in the

agglomeration of the materials prepared with a surfactant26

However this occurs at the expense of possible environmental

pollution due to surfactant leaching during the application (if

the surfactant is not removed) and a higher production cost

Fig 1 XRD patterns (a) and FTIR spectra (b) of the as-prepared cata-

lysts frac14 Fe2O3 frac14 Cu and frac14 CuO


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The low temperature co-precipitation method produces Fe2O3

with a high surface area due to the employment of dipicolinic

acid (DPA) for synthesis control13 However CuFe2O4ndashFe2O3

could not be formed in the presence of DPA possibly due to the

complexation of Cu with DPA making it less available for

reaction


321 Comparison of various catalysts Fig 4 shows the

performance comparison of various catalysts namely CuFe2O4ndash

Fe2O3 Fe2O3 CuX 2O4 (X frac14 Fe Bi and Al) and YFe2O4 (Y frac14 Cu Coand Mn) for BPA degradation via PMS activation at various time

intervals while Table 1 shows the BET specic surface area TOC

removal rst-order rate constant (k app) and Cu leaching for

various catalysts The catalysts were compared with respect to

diff erent synthesis methods (ie solvothermal CuFe2O4 vs low

temperature co-precipitation CuFe2O4) and diff erent mixed

metal oxide systems (ie CuX 2O4 (X frac14 Fe Bi and Al) and YFe2O4

(Y frac14 Cu Co and Mn)) The metal oxide catalysts contain a

transition metal (Men+) which can activate PMS to produce

SO4c for degrading BPA through the following single electron

transfer reaction

Men+ + HSO5Me(n+1)+ + SO4c + OH (1)

Me(n+1)+ + HSO5

Men+ + SO5c + H+ (2)

SO4c + BPA degradation by-products (3)

There was no signicant BPA removal (lt5 in 30 min) by

adsorption and PMS oxidation The performance of the

CuFe2O4ndashFe2O3 catalyst synthesized in 3 6 and 12 h was almost

the same as that of the catalyst synthesized in 24 h (Fig S2adagger)

However the CuFe2O4ndashFe2O3 synthesized in 24 h was selected

for further performance evaluation as it is relatively more stable

(less amorphous) with a homogeneous morphology as

compared with the others Several other PMS dosages were also

Fig 3 Schematic illustration of the low temperature CuFe2O4ndashFe2O3

synthesis protocol Nucleation of the CuFe2O4ndashFe2O3 catalyst occurs

when themetalprecursor is subjected to 95 C under basic conditions

The CuFe2O4ndashFe2O3 nucleus proceeds to grow and self-assemble to

form the cubic microstructure

Fig 4 BPA degradation curves for different catalysts Initial condi-

tions [pH] frac14 70 02 [PMS] frac14 036 g L1 [catalyst] frac14 02 g L1 and

[BPA] frac14 5 mg L1

Fig 2 (andashd) Time dependent FESEM micrographs (e) EDX elemental

mappings(f) time-dependent XRDpatterns and(g) FTIR spectra of the

pristine and used CuFe2O3ndashFe2O3 catalyst



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investigated prior to the performance comparison study

(Fig S2bdagger) The activities of the catalysts are in the following

order CuFe2O4ndashFe2O3 gt CuFe2O4 gt CoFe2O4 gt CuBi2O4 gt

CuAl2O4 gt Fe2O3 gt MnFe2O4 The CuFe2O4ndashFe2O3 catalyst per-

formed better than all the other catalysts due to several factors

namely (i) its eco-friendly preparation method without using

any organic precursorsolvent whose residue in the resulting catalyst could reduce its catalytic activity and (ii) efficient

synergistic Cu and Fe redox coupling in the metal oxide

framework which has a promotional eff ect on the PMS activa-

tion72224 The TOC removal efficiency of CuFe2O4ndashFe2O3 was

24 but by prolonging the reaction time to 6 h the TOC

removal efficiency increased to 52 The use of an organic

precursorsolvent (ie surfactant) for the synthesis could result

in the formation of surface-bound organics which are difficult

to be removed without using extreme heat treatment These

surface-bound organics could compete for reaction with SO4c

and prevent the eff ective utilization of the generated radicals for

pollutant degradation This phenomenon explains the lower

catalytic performance of the solvothermally prepared CuFe2O4

and CoFe2O4 (k app frac14 052 002 and 038 001 respectively)

compared with that of the CuFe2O4ndashFe2O3 catalyst despite

having a higher surface area for catalysis In addition the

degradation of the surface-bound organics has the tendency of

causing unfavourable TOC leaching which explains the

observed negative TOC removal efficiencies when CuFe2O4

CoFe2O4 and MnFe2O4 prepared by using a solvothermal

method were employed as the catalyst for BPA treatment

The redox transition between Cu2+ndashCu+

ndashCu2+ in the presence

of PMS yields both SO5c and SO4c

Compared to Cu2+ the Cu+

species is relatively unstable and can be easily scavenged (eg by

the dissolved oxygen) Considering the thermodynamic feasi-bility of the following reaction Cu+ + Fe3+ Cu2+ + Fe2+ ( E o frac14

+060 V) the Fe3+ species acts as an intermediate electron

acceptor and reduces the amount of Cu+ scavenged In this

regard the CuFe2O4ndashFe2O3 catalyst has an advantage over

CuFe2O4 by having higher amounts of Fe3+ which could

decrease Cu+ scavenging and maximize the production of SO4c

thus enhancing the BPA degradation rate

Since Cu2+ is the active species in the CuFe2O4ndashFe2O3 catalyst

for PMS activation Cu leaching for all the Cu catalysts was

compared The Cu leaching during PMS activation of the

CuFe2O4ndashFe2O3 catalyst was comparable with that of the

solvothermally prepared CuFe2O4 ferrospinel (09 mg L1 or

005 vs 07 mg L1 or 004 respectively) However the

CuFe2O4ndashFe2O3 catalyst prepared with a 3 h synthesis time

exhibited 153 mg L1 of Cu leaching or 1 of the total

catalyst weight loss further indicating that a relatively longer

preparation time of 24 h is necessary to improve the crystallinity

and stability of the CuFe2O4ndash

Fe2O3 catalyst for low temperaturesynthesis of the catalyst

322 Eff ects of pH catalyst loading and PMS dosage

Fig 5ndash7 show the inuence of several key parameters namely

the pH PMS dosage and catalyst loading on BPA removal The

Table 1 Synthesis method BET speci1047297c surface area TOC removal efficiency Cu leaching and pseudo 1047297rst-order rate constant (k app) values of

various catalystsa

Catalyst Synthesis methodSpecic surfacearea (m2 g 1)

TOC removal efficiency at 30 min () Cu leaching (mg L1) k app

CuFe2O4ndashFe2O3 Low-temperature co-precipitation 63 24 (52) 09 (lt01) 062 004CuFe2O4 Solvothermal 101 23 07 (lt01) 052 002CuBi2O4 Low temperature co-precipitation 9 15 06 (lt01) 008 001CuAl2O4 Solndashgel 39 13 02 (lt01) 007 000

MnFe2O4 Solvothermal 151 12 mdash 004 000CoFe2O4 Solvothermal 139 32 mdash 038 001Fe2O3 Low-temperature co-precipitation 188 11 mdash 005 000

a () indicates TOC removal at t frac14 6 h

Fig 5 Experimental and calculated BPA degradation curves for

different PMS dosages at various catalyst loadings Initial conditions

[pH] frac14 45 02 and [BPA] frac14 5 mg L1



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pHzpc of CuFe2O4ndashFe2O3 is determined to be pH 76 (Fig S2cdagger)

Generally the removal efficiency and rate improved with

increasing pH PMS dosage and catalyst loading Pseudo-rst order kinetics was employed to model the BPA degradation rate

and the calculated pseudo rst-order rate constant (k app) under

diff erent conditions is presented in Table 2 While the pseudo

rst-order ttings at pH values 70 and 95 are generally good ( R2

gt 09) the tting at pH 45 is relatively poorer due to the over-

simplication of the kinetic model which adopts a ldquoblack-box rdquo

approach The pseudo rst-order kinetics did not take into

account the change of catalyst surface charge (eqn (4)) and

possible attachment of the protons to the more electronegative

peroxide bond of the PMS molecule (eqn (5)) at acidic pH which

gives rise to the interfacial repulsion leading to a weaker cata-

lytic performance13

[Cat OH] + H+4 [Cat OH+

2 ] (4)

SO2 ndashOndashOndashH + H+ SO2 ndashOndashOndashH2

+ (5)

where [Cat OH] and [Cat OH2+] are the densities of active

and deactivated catalytic sites respectively The catalyst surface

contains many surface hydroxyl moieties which are important

for PMS activation and surface protonation inuences the

density of surface hydroxyl moieties The eff ect was particularly

more pronounced at lower catalyst loading and PMS dosage

To address the limitation of the pseudo rst-order kinetics a

kinetic model based on the mechanistic consideration that thecatalytic sites could be partially deactivated as a result of surface

protonation is adopted in this study Under equilibrium

conditions the thermodynamic equilibrium constant ( K eq) for

eqn (4) can be expressed as follows

K eq frac14 frac12Cat OHo frac12Cat OH

Hthornfrac12Cat OH

(6)

where [Cat OH]o is the catalyst loading By incorporating the

variables consisting of the catalyst loading and PMS dosage into

the kinetic model the rate of BPA removal can be given as

follows

dC

BPAdt frac14 k ifrac12Cat OHC BPAC PMS (7)

where C BPA and C PMS are the concentrations of BPA and PMS

respectively and k i is the intrinsic reaction rate constant

Considering that the changes of the C PMS follows the rst-order

kinetics (Fig S3dagger) and by incorporating eqn (6) into (7) the

kinetic model can be further simplied as follows

dC BPA

dt frac14 k i

frac12Cat OHoK eq

Hthorn

thorn 1

C BPAC PMSoek PMSt (8)









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where k PMS is the rst-order rate constant for PMS consump-tion Eqn (8) can be solved analytically to become eqn (9) by

integrating with respect to t under the following boundary

conditions at t frac14 0 C BPA frac14 C BPAo

C BPA frac14 C BPAoe

k i

k PMS

frac12CatOHo

ethK eq frac12Hthorn thorn1THORN

C PMSoethek 2t 1THORN(9)

Eqn (9) will be explicitly validated by tting with the experi-

mentally obtained BPA degradation results using Matlab and

the kinetic parameters can be calculated by optimization using

the nonlinear least squares method Preliminary ttings indi-

cated that all K eq have a value close to 10 The K eq frac14 1 indicates

that neither the [Cat OH2+] nor the [Cat OH] are favoured

species and the equilibrium is dependent on pH (ie when [H+]

is higher at acidic pH the [Cat OH2+][Cat OH] is higher)

Therefore K eq was used as a constant for the subsequent kinetic

modelling studies

Table 2 also shows the calculated kinetic parameters con-

sisting of k i and k PMS with their respective R2 When the PMS is

readily available for activation without signicant inuence by

the pH (rst-order) the relationship between k app and k i can be

established by using the following equation

k t frac14 k app

K eq

Hthorn

thorn 1

frac12Cat OHofrac12PMSo

(10)

A relatively good t was observed for all cases ( R2 gt 099)

indicating that the kinetic model is able to account for the eff ect

of diff erent reaction pH values In general the trend of k i value

decreases linearly with increasing catalyst loading suggesting

that the BPA oxidation reaction per unit catalyst proceeds

slower at higher catalyst loading It should be noted that k i has

been normalized with respect to the catalyst loading and PMS

dosage This was also observed previously for the k i values

calculated from eqn (10) in other heterogeneous PMS systems

employing pseudo-rst-order kinetics to model the pollutant

degradation rate1427 This observation could be due to the fact

that PMS activation by using CuFe2O3ndashFe2O3 is a multi-step

activation process generating both SO4c and SO5c

for BPA

degradation (eqn (11)ndash(14))222

Cu2+ + HSO5

Cu+ + SO5c + H+ (11)

Cu+ + HSO5

Cu2+ + SO4c + OH (12)

Fe3+ + HSO5

Fe2+ + SO5c + H+ (13)

Table 2 Kinetic parameters of CuFe2O4ndashFe2O3 catalyzed BPA degradation via PMS activation under various conditions

PMS dosage (g L1) Catalyst loading (g L1) k app R2 k i k PMS R2

pH 45

018 005 0031 0002 019 607 125 022 004 0996010 0046 0001 021 485 050 023 003 0991020 013 001 095 215 015 0050 0003 0999

027 005 0043 0003 047 385 007 015 001 0998010 0062 0001 049 327 018 019 001 0985

020 017 001 083 213 008 007 001 0999036 005 0067 0001 049 459 006 015 000 0997

010 0083 0003 059 271 006 015 001 0995020 023 002 090 198 004 006 002 0996

pH 70

018 005 011 001 099 498 041 002 001 0996010 016 001 099 468 029 004 001 0999020 046 004 098 413 018 0004 0002 0999

027 005 014 001 096 418 010 0016 0002 0999010 024 001 098 403 002 003 001 0999020 053 007 091 543 010 011 002 0999

036 005 014 001 090 416 020 0043 0001 0999010 028 004 096 398 033 005 001 0999020 062 004 099 400 000 0002 0001 0999

pH 90

018 005 033 001 097 1705 037 002 001 0999010 056 001 088 1670 062 009 001 0999020 069 002 091 1288 111 024 003 0999

027 005 075 012 098 2477 060 011 007 0999010 090 008 097 1652 164 018 013 0999020 166 041 099 1314 207 017 008 0999

036 005 090 008 093 3288 132 030 008 0999010 123 004 098 1654 138 019 005 0999020 141 011 099 1371 107 076 001 0999



View Article Online



Fe2+ + HSO5

Fe3+ + SO4c + OH (14)

The catalyst consists predominantly of transition metals at a

higher oxidation state (ie Cu2+ and Fe3+) which favours the

generation of SO5c during the initial major activation steps

(eqn (11)ndash(13)) When a higher catalyst loading is employed a

higher amount of PMS is instantaneously converted to SO5c

rst for BPA oxidation resulting in less PMS available for

producing SO4c

SO5c

is a considerably weaker radical thanSO4c

which lowers the BPA degradation rate13 While the redox

reaction also produces Fe2+ which is critical to generate SO4c

excessive Fe2+ generated from SO5c production at higher

catalyst loading acts as a strong quencher for SO4c2829

Fe2thorn thorn SO4cFe3thorn thorn SO4

2k Fe2thornthornSOc

4frac14 3 108 M1 s1

(15)

As such it can be construed that at lower catalyst loading

PMS can be utilized more efficiently to generate SO4c for BPA

degradation All the k i values at pH 95 are signicantly higher

than those at pH values 45 and 70 attributed to the productionof HOc Under alkaline conditions synergistic BPA degradation

by both SO4c and HOc occurs No consistent trend for k PMS was

observed which could be due to the complex interaction of PMS

with diff erent generated radicals (eg SO4c HOc SO5c

etc)29ndash31 The PMS could also react with both the BPA and its

intermediates

HSO5 thorn SO4

cSO5

c thorn SO42 thorn Ηthorn

ethk HSO5thornSO4 c

frac14 1 105 M1 s1THORN (16)

HSO5 thorn HOcSO5


ethk HSO5thornHOc frac14 1 107 M1 s1THORN

(17)

HSO5 + SO5c

+ H2O SO4c + SO4

2 + O2 + H3O+ (18)

HSO5 + SO5c

+ H2O HOc + 2SO42 + O2 + 2H+ (19)

323 Eff ects of water matrix species Fig 8a shows the

eff ects of various water matrix species (Cl NO3 HCO3

PO43 and HA) on BPA degradation A kinetic model (eqn (9))

was used to describe the BPA degradation rate in the presence of

diff erent water matrix species and their respective intrinsic rate

constants k i ( R2 gt 099) are presented in Fig 8b The concen-

trations of water matrix species were selected to resemble the

typical characteristics of wastewater The results indicated that

Cl and HA exerted a signicant negative impact while the

NO3 HCO3

and PO43 anions did not have a signicant

impact on the BPA degradation It is known that the Cl anion

could quench the generated SO4c to produce weaker radicals

(Clc and Cl2c as shown in eqn (20) and (21) respectively) and

HClO3233 while HA consumes PMS and competes with BPA for

the reactive SO4c and PMS (eqn (22) and (23)) thus retarding

the BPA degradation reaction Moreover HA could also foul the

catalyst leading to the deactivation of the catalytic active sites

for PMS activation34

Cl thorn SO4cClcthorn SO4

2

ethk ClthornSO4c frac14 2

8 108 M1 s1THORN (20)

Cl thorn ClcCl2c

k ClthornClc frac14 8 109 M1 s1 (21)

Humic acid + HSO5

by-products + SO42 (22)

Humic acid + SO4c


A previous report has indicated that a PO43 anion at natural

pH can induce the formation of SO4c from PMS which could

have a positive eff

ect on BPA degradation However a higherPO43 concentration of up to 9 g L1 than that used in this study

(100 mg L1) was required to have a signicant eff ect35 The

HCO3 anion is a strong SO4c

and OHc quencher (eqn (24) and

(25)) and previous studies have reported that it could induce a

detrimental eff ect on the BPA degradation rate but this was not

observed in this study due to the use of a lower HCO3-concentration in this study36

HCO3 thorn SO4

cSO4

2 thorn CO3c thornΗthorn

ethk HCO3thornSO4 c

frac14 16 106 M1 s1THORN (24)

Fig 8 (a) Effects of different water matrix species on the BPA

degradation and (b) k i values Initial conditions [pH] frac14 70 02 [PMS]

frac14 018 g L1 [catalyst] frac14 005 g L1 and [BPA] frac14 5 mg L1



View Article Online



HCO3 thorn OHcCO3c thorn Η2O

k HCO3thornOHc frac14 85 106 M1 s1

(25)

33 Catalyst stability and reusability

Fig 9 shows the reusability of CuFe2O3ndashFe2O3 for BPA removal

via PMS activation over 3 cycles A er 3 consecutive cycles the

rate of BPA removal decreased slightly This could be due to the

adsorption of BPA degradation intermediates on the catalyst

surface as evidenced by the presence of an additional absor-

banceband at 1000 cm1 in the FTIR spectra of the used catalyst

(Fig 2g) which could be attributed to CndashO stretching of the

aromatic ring The catalyst can be reused with no signicant

diff erence in the performance by simple washing and drying indicating that the low-temperature synthesis method could

produce a stable efficient and easily regenerable catalyst for

generating SO4c from PMS

4 Conclusions

The CuFe2O3ndashFe2O3 catalyst was successfully synthesized via an

eco-friendly co-precipitation protocol at low temperature to

generate sulfate radicals from PMS for BPA removal The

mechanism of the formation of CuFe2O3ndashFe2O3 at low temper-

ature is proposed The CuFe2O3ndashFe2O3 catalyst performed

signi

cantly better than other catalysts namely ferrospinels(YFe2O4 Y frac14 Cu Co and Mn) Cu-based spinels (CuX 2O4 X frac14 Bi

and Al) and Fe2O3 due to its preparation method without the

use of organic precursors and efficient synergistic redox

coupling between Cu2+ and Fe3+ A kinetic model was developed

based on the mechanistic consideration of the inuences of

various operating parameters namely pH PMS dosage and

catalyst loading The proposed mechanistic kinetic model tted

relatively better than the pseudo-rst order kinetics which did

not take into consideration the pH-dependent surface-charge

eff ect The relationship between the pseudo rst-order rate

constant (k app) and the intrinsic rate constant (k i) was

established The presence of chloride and humic acid in the

solution could signicantly aff ect the BPA degradation rate

This work provides new insights into the use of environmentally

benign catalysts for efficient degradation of xenobiotic pollut-

ants via sulfate radical-based advanced oxidation processes

Acknowledgements

The nancial support from Academic Research Fund RG7612 is

gratefully acknowledged The authors would also like to thank

the interdisciplinary graduate school (IGS) and Nanyang Envi-

ronment and Water Research Institute (NEWRI) for the award of

PhD research Scholarship The kind assistance from all the

technical staff in the Environmental Laboratories is deeply

appreciated

References

1 G P Anipsitakis D D Dionysiou and M A Gonzalez

Environ Sci Technol 2005 40 10002 W-D Oh S-K Lua Z Dong and T-T Lim J Hazard Mater

2015 284 1

3 G P Anipsitakis and D D Dionysiou Environ Sci Technol

2004 38 3705

4 Y Hardjono H Sun H Tian C E Buckley and S Wang

Chem Eng J 2011 174 376

5 Z Huang H Bao Y Yao W Lu and W Chen Appl Catal B

2014 154ndash155 36

6 Y Ding L Zhu N Wang and H Tang Appl Catal B 2013

129 153

7 T Zhang H Zhu and J-P Croue Environ Sci Technol 2013

47 2784

8 F Ji C Li and L Deng Chem Eng J 2011 178 2399 F Ji C Li Y Liu and P Liu Sep Purif Technol 2014 135 1

10 J I Eid S M Eissa and A A El-Ghor J Basic Appl Zool

2015 71 10

11 J R Rochester Reprod Toxicol 2013 42 132

12 T Olmez-Hanci D Dursun E Aydin I Arslan-Alaton

B Girit L Mita N Diano D G Mita and M Guida

Chemosphere 2015 119 S115

13 W-D Oh S-K Lua Z Dong and T-T Lim J Mater Chem A

2014 2 15836

14 J Liu Z Zhao P Shao and F Cui Chem Eng J 2015 262

854

15 J Zhang X Shao C Shi and S Yang Chem Eng J 2013232 259

16 F Qi W Chu and B Xu Chem Eng J 2014 235 10

17 B K Kwak D S Park Y S Yun and J Yi Catal Commun

2012 24 90

18 H Deng H Chen and H Li Mater Chem Phys 2007 101

509

19 Y Yao Y Cai F Lu F Wei X Wang and S Wang J Hazard

Mater 2014 270 61

20 M V Lopez-Ramon F Stoeckli C Moreno-Castilla and

F Carrasco-Marin Carbon 1999 37 1215

21 J Li J Zhu and X Liu Dalton Trans 2014 43 132ndash137

Fig 9 Reusability of the CuFe2O3ndashFe2O3 catalyst Initial conditions

pH frac14 70 02 [PMS] frac14 018 g L1 [catalyst] frac14 005 g L1 and [BPA] frac145 mg L1



View Article Online



22 Y Ren L Lin J Ma J Yang J Feng and Z Fan Appl Catal

B 2015 165 572

23 W Zhang H L Tay S S Lim Y Wang Z Zhong and R Xu

Appl Catal B 2010 95 93

24 Y-H Guan J Ma Y-M Ren Y-L Liu J-Y Xiao L-Q Lin

and C Zhang Water Res 2013 47 5431

25 Z-T Hu B Chen and T-T Lim RSC Adv 2014 4 27820

26 X Chen W Cai C Fu H Chen and Q Zhang J Sol-Gel Sci

Technol 2011 57 14927 C Tan N Gao Y Deng J Deng S Zhou J Li and X Xin J

Hazard Mater 2014 276 452

28 A Rastogi S R Al-Abed and D D Dionysiou Appl Catal B

2009 85 171

29 C Brandt and R van Eldik Chem Rev 1995 95 119

30 O Gimeno J Rivas M Carbajo and T Borralho World

2009 57 223

31 T Balakrishnan and S D Kumar J Chem Sci 2000 112

497

32 W-D Oh S-K Lua Z Dong and T-T Lim Nanoscale 2015

7 8149

33 P Wang S Yang L Shan R Niu and X Shao J Environ Sci

2011 23 1799

34 B P Chaplin E Roundy K A Guy J R Shapley andC J Werth Environ Sci Technol 2006 40 3075

35 X Lou L Wu Y Guo C Chen Z Wang D Xiao C Fang

J Liu J Zhao and S Lu Chemosphere 2014 117 582

36 J Sharma I M Mishra D D Dionysiou and V Kumar

Chem Eng J 2015 276 193



View Article Online



carbon adsorption these methods require high energy

consumption or generate a secondary waste stream13

Previous investigation of the kinetics of pollutant oxidation

by using sulfate radicals in the heterogeneous system was o en

based on the pseudo rst-order kinetics with the assumption

that the oxidant (PMS) added was readily available for reac-

tion1415 Qi et al presented a second-order kinetic model to

describe the degradation of caff eine by using a Co-MCM41

catalyst16 However these kinetic models did not take intoaccount the inuence of pH PMS dosage and catalyst loading

on pollutant degradation particularly under non-ideal condi-

tions (eg non-excess PMS diff erent pH values etc) In this

regard a more robust kinetic model needs to be employed

Herein the objectives of this study are to (i) prepare and

characterize a series of catalysts encompassing CuFe2O4ndashFe2O3

ferrospinels (YFe2O4 Y frac14 Cu Co and Mn) Cu-based spinels

(CuX 2O4 X frac14 Bi and Al) and Fe2O3 (ii) investigate and compare

the performance of the as-prepared catalysts for BPA removal

via PMS activation and (iii) develop a kinetic model based on

the mechanistic consideration of various inuencing parame-

ters (ie pH PMS dosage and catalyst loading) to describe theBPA degradation The intrinsic rate constant k i was calculated

explicitly from the experimentally derived BPA degradation at

various time intervals in the kinetic modelling study and it was

compared with the pseudo rst-order rate constant (k app) to

obtain new insights into the use of heterogeneous transition

metal catalysts for pollutant removal via PMS activation

2 Experimental21 Chemicals

All the chemicals used in this study are of analytical grade The

chemicals used are as follows Cu(NO3)2$3H2O (QreC)

Co(NO3)2$6H2O (Alfa Aesar) Mn(NO3)2$4H2O (Sigma-Aldrich)

Fe(NO3)3$9H2O (Merck) Bi(NO3)3$5H2O (Alfa Aesar)

Al(NO3)3$9H2O (Sigma-Aldrich) NaOH (Alfa Aesar) HCl (Merck)

acetonitrile (Merck) citric acid (Merck) ammonia (Hach) KI

(Fisons) PMS (in the form of Oxonereg 2KHSO5$KHSO4$K2SO4

Alfa Aesar) NaCl (Qrectrade) NaNO3 (Sigma-Aldrich) humic acid

(HA Aldrich) NaHCO3 (Sigma-Aldrich) polyethylene glycol

(Sigma-Aldrich) sodium acetate (Sigma-Aldrich) bisphenol A

(Merck) and methanol (Merck) All the experiments were con-

ducted using deionized (DI) water (182 MU cm)

22 Synthesis of catalysts

The CuFe2O4ndashFe2O3 catalyst was prepared using a facile co-

precipitation method at low temperature In a typical synthesis

procedure metal precursors consisting of 5 mmol of

Cu(NO3)2$3H2O and 10 mmol of Fe(NO3)3$9H2O were dissolved

in 50 mL of DI water and the pH of the solution mixture was

adjusted to pH 10ndash11 using 6 M NaOH under rapid magnetic

stirring Then the resultant solution was heated under vigorous

stirring at 95 C for 24 h to promote hydrolysis and the

formation of the CuFe2O4ndashFe2O3 catalyst The resultant

brownish product was separated from the solution by using a

simple magnetic separation procedure and freeze-dried for 24

h Several other catalysts namely CuAl2O4 CuBi2O4 CuFe2O4

MnFe2O4 CoFe2O4 and Fe2O3 were also prepared for perfor-

mance comparison with CuFe2O4ndashFe2O3 CuAl2O4 was prepared

via a solndashgel method17 CuBi2O4 and Fe2O3 were prepared via a

low-temperature co-precipitation method13 XFe2O4 (X frac14 Mn Fe

and Co) was prepared via a solvothermal method18 The details

of the synthesis procedures for preparing ferrospinels (YFe2O4

Y frac14 Cu Co and Mn) Cu-based spinels (CuX 2O4 X frac14 Bi and Al)

and Fe2O3 are presented in the ESIdagger

23 Characterization technique

The crystallographic and mineralogical information of the as-

prepared catalysts was obtained using a X-ray diff ractometer

(Bruker AXS D8 Advance) operating at 40 kV and 40 mA with a

Cu-Ka (l frac14 15418 ˚ A) X-ray source The surface morphology and

EDX elemental distribution were studied by obtaining the

electron micrographs and elemental mappings using a eld

emission scanning electron microscope (FESEM JEOL JSM-

7600F) equipped with an energy dispersive X-ray spectrometer

(EDX Oxford Xmax80 LN2 Free) The Fourier transform infrared(FTIR) spectra were obtained using a FTIR spectrometer (Perkin

Elmer Spectrum GX) The BrunauerndashEmmett ndashTeller (BET)

specic surface area of the catalysts was calculated from the N2

adsorptionndashdesorption isotherm analysis at 77 K (Quantach-

rome Autosorb-1 Analyzer)


Batch experiments were conducted to investigate the perfor-

mance of the catalyst for BPA treatment via PMS activation In

a typical experimental procedure a known amount of PMS

was introduced into the reaction vessels containing 100 mL of

5 mg L1 of BPA at 25 C The pH of the solution was imme-diately adjusted to the desired pH (pH 45 70 or 95) Then a

known amount of the catalyst was added into the solution to

commence the catalytic reaction At various time intervals

2 mL aliquots were sampled from the reaction vessel to

determine the BPA concentration The collected aliquots were

ltered using a cellulose acetate membrane lter and the

catalytic reaction was quenched using methanol The BPA

concentration was then determined by using high perfor-

mance liquid chromatography (HPLC) At the end of the

reaction time the pH change of the solution at pH 45 was

insignicant while for pH 70 and 95 the nal pH was 61 and

81 respectively due to their unbuff

ered condition and theformation of acidic BPA intermediates such as organic acids13

The experimental parameters studied were the PMS dosage

(018 027 and 036 g L1) catalyst loading (005 010 and

020 g L1) and initial pH (45 70 and 95) The mole ratio of

PMS to pollutant used in this study was comparable to that of

another study19 At the end of the reaction time the total

organic carbon and Cu leaching were also determined for the

selected conditions For the TOC determination the samples

were ltered and analyzed immediately without quenching

with methanol Investigation of the changes in PMS concen-

tration over time was also conducted



View Article Online


























curve



























rate

2223


1








































View Article Online








reaction














transfer reaction


Me(n+1)+ + HSO5

Men+ + SO5c + H+ (2)























View Article Online


























































various catalystsa











View Article Online
















lytic performance13


2 ] (4)


+ (5)













Hthornfrac12Cat OH

(6)




follows

dC







dC BPA

dt frac14 k i

frac12Cat OHoK eq

Hthorn

thorn 1










View Article Online







k i

k PMS

frac12CatOHo












modelling studies






k t frac14 k app

K eq

Hthorn

thorn 1


(10)














for BPA


Cu2+ + HSO5

Cu+ + SO5c + H+ (11)

Cu+ + HSO5

Cu2+ + SO4c + OH (12)

Fe3+ + HSO5

Fe2+ + SO5c + H+ (13)



pH 45

018 005 0031 0002 019 607 125 022 004 0996010 0046 0001 021 485 050 023 003 0991020 013 001 095 215 015 0050 0003 0999

027 005 0043 0003 047 385 007 015 001 0998010 0062 0001 049 327 018 019 001 0985

020 017 001 083 213 008 007 001 0999036 005 0067 0001 049 459 006 015 000 0997

010 0083 0003 059 271 006 015 001 0995020 023 002 090 198 004 006 002 0996

pH 70

018 005 011 001 099 498 041 002 001 0996010 016 001 099 468 029 004 001 0999020 046 004 098 413 018 0004 0002 0999

027 005 014 001 096 418 010 0016 0002 0999010 024 001 098 403 002 003 001 0999020 053 007 091 543 010 011 002 0999

036 005 014 001 090 416 020 0043 0001 0999010 028 004 096 398 033 005 001 0999020 062 004 099 400 000 0002 0001 0999

pH 90

018 005 033 001 097 1705 037 002 001 0999010 056 001 088 1670 062 009 001 0999020 069 002 091 1288 111 024 003 0999

027 005 075 012 098 2477 060 011 007 0999010 090 008 097 1652 164 018 013 0999020 166 041 099 1314 207 017 008 0999

036 005 090 008 093 3288 132 030 008 0999010 123 004 098 1654 138 019 005 0999020 141 011 099 1371 107 076 001 0999



View Article Online



Fe2+ + HSO5

Fe3+ + SO4c + OH (14)







producing SO4c

SO5c







2k Fe2thornthornSOc

4frac14 3 108 M1 s1

(15)









intermediates

HSO5 thorn SO4

cSO5


ethk HSO5thornSO4 c

frac14 1 105 M1 s1THORN (16)

HSO5 thorn HOcSO5



(17)

HSO5 + SO5c

+ H2O SO4c + SO4

2 + O2 + H3O+ (18)

HSO5 + SO5c

+ H2O HOc + 2SO42 + O2 + 2H+ (19)










NO3 HCO3











2


8 108 M1 s1THORN (20)

Cl thorn ClcCl2c


Humic acid + HSO5


Humic acid + SO4c




have a positive eff








HCO3 thorn SO4

cSO4


ethk HCO3thornSO4 c

frac14 16 106 M1 s1THORN (24)






View Article Online





(25)













4 Conclusions






signi

















Acknowledgements







appreciated

References



2015 284 1


2004 38 3705


Chem Eng J 2011 174 376


2014 154ndash155 36


129 153


47 2784



2015 71 10






2014 2 15836


854




2012 24 90


509


Mater 2014 270 61








View Article Online




B 2015 165 572










2009 85 171



2009 57 223


497


7 8149


2011 23 1799





Chem Eng J 2015 276 193



View Article Online


























curve



























rate

2223


1








































View Article Online








reaction














transfer reaction


Me(n+1)+ + HSO5

Men+ + SO5c + H+ (2)























View Article Online


























































various catalystsa











View Article Online
















lytic performance13


2 ] (4)


+ (5)













Hthornfrac12Cat OH

(6)




follows

dC







dC BPA

dt frac14 k i

frac12Cat OHoK eq

Hthorn

thorn 1










View Article Online







k i

k PMS

frac12CatOHo












modelling studies






k t frac14 k app

K eq

Hthorn

thorn 1


(10)














for BPA


Cu2+ + HSO5

Cu+ + SO5c + H+ (11)

Cu+ + HSO5

Cu2+ + SO4c + OH (12)

Fe3+ + HSO5

Fe2+ + SO5c + H+ (13)



pH 45

018 005 0031 0002 019 607 125 022 004 0996010 0046 0001 021 485 050 023 003 0991020 013 001 095 215 015 0050 0003 0999

027 005 0043 0003 047 385 007 015 001 0998010 0062 0001 049 327 018 019 001 0985

020 017 001 083 213 008 007 001 0999036 005 0067 0001 049 459 006 015 000 0997

010 0083 0003 059 271 006 015 001 0995020 023 002 090 198 004 006 002 0996

pH 70

018 005 011 001 099 498 041 002 001 0996010 016 001 099 468 029 004 001 0999020 046 004 098 413 018 0004 0002 0999

027 005 014 001 096 418 010 0016 0002 0999010 024 001 098 403 002 003 001 0999020 053 007 091 543 010 011 002 0999

036 005 014 001 090 416 020 0043 0001 0999010 028 004 096 398 033 005 001 0999020 062 004 099 400 000 0002 0001 0999

pH 90

018 005 033 001 097 1705 037 002 001 0999010 056 001 088 1670 062 009 001 0999020 069 002 091 1288 111 024 003 0999

027 005 075 012 098 2477 060 011 007 0999010 090 008 097 1652 164 018 013 0999020 166 041 099 1314 207 017 008 0999

036 005 090 008 093 3288 132 030 008 0999010 123 004 098 1654 138 019 005 0999020 141 011 099 1371 107 076 001 0999



View Article Online



Fe2+ + HSO5

Fe3+ + SO4c + OH (14)







producing SO4c

SO5c







2k Fe2thornthornSOc

4frac14 3 108 M1 s1

(15)









intermediates

HSO5 thorn SO4

cSO5


ethk HSO5thornSO4 c

frac14 1 105 M1 s1THORN (16)

HSO5 thorn HOcSO5



(17)

HSO5 + SO5c

+ H2O SO4c + SO4

2 + O2 + H3O+ (18)

HSO5 + SO5c

+ H2O HOc + 2SO42 + O2 + 2H+ (19)










NO3 HCO3











2


8 108 M1 s1THORN (20)

Cl thorn ClcCl2c


Humic acid + HSO5


Humic acid + SO4c




have a positive eff








HCO3 thorn SO4

cSO4


ethk HCO3thornSO4 c

frac14 16 106 M1 s1THORN (24)






View Article Online





(25)













4 Conclusions






signi

















Acknowledgements







appreciated

References



2015 284 1


2004 38 3705


Chem Eng J 2011 174 376


2014 154ndash155 36


129 153


47 2784



2015 71 10






2014 2 15836


854




2012 24 90


509


Mater 2014 270 61








View Article Online




B 2015 165 572










2009 85 171



2009 57 223


497


7 8149


2011 23 1799





Chem Eng J 2015 276 193



View Article Online








reaction














transfer reaction


Me(n+1)+ + HSO5

Men+ + SO5c + H+ (2)























View Article Online


























































various catalystsa











View Article Online
















lytic performance13


2 ] (4)


+ (5)













Hthornfrac12Cat OH

(6)




follows

dC







dC BPA

dt frac14 k i

frac12Cat OHoK eq

Hthorn

thorn 1










View Article Online







k i

k PMS

frac12CatOHo












modelling studies






k t frac14 k app

K eq

Hthorn

thorn 1


(10)














for BPA


Cu2+ + HSO5

Cu+ + SO5c + H+ (11)

Cu+ + HSO5

Cu2+ + SO4c + OH (12)

Fe3+ + HSO5

Fe2+ + SO5c + H+ (13)



pH 45

018 005 0031 0002 019 607 125 022 004 0996010 0046 0001 021 485 050 023 003 0991020 013 001 095 215 015 0050 0003 0999

027 005 0043 0003 047 385 007 015 001 0998010 0062 0001 049 327 018 019 001 0985

020 017 001 083 213 008 007 001 0999036 005 0067 0001 049 459 006 015 000 0997

010 0083 0003 059 271 006 015 001 0995020 023 002 090 198 004 006 002 0996

pH 70

018 005 011 001 099 498 041 002 001 0996010 016 001 099 468 029 004 001 0999020 046 004 098 413 018 0004 0002 0999

027 005 014 001 096 418 010 0016 0002 0999010 024 001 098 403 002 003 001 0999020 053 007 091 543 010 011 002 0999

036 005 014 001 090 416 020 0043 0001 0999010 028 004 096 398 033 005 001 0999020 062 004 099 400 000 0002 0001 0999

pH 90

018 005 033 001 097 1705 037 002 001 0999010 056 001 088 1670 062 009 001 0999020 069 002 091 1288 111 024 003 0999

027 005 075 012 098 2477 060 011 007 0999010 090 008 097 1652 164 018 013 0999020 166 041 099 1314 207 017 008 0999

036 005 090 008 093 3288 132 030 008 0999010 123 004 098 1654 138 019 005 0999020 141 011 099 1371 107 076 001 0999



View Article Online



Fe2+ + HSO5

Fe3+ + SO4c + OH (14)







producing SO4c

SO5c







2k Fe2thornthornSOc

4frac14 3 108 M1 s1

(15)









intermediates

HSO5 thorn SO4

cSO5


ethk HSO5thornSO4 c

frac14 1 105 M1 s1THORN (16)

HSO5 thorn HOcSO5



(17)

HSO5 + SO5c

+ H2O SO4c + SO4

2 + O2 + H3O+ (18)

HSO5 + SO5c

+ H2O HOc + 2SO42 + O2 + 2H+ (19)










NO3 HCO3











2


8 108 M1 s1THORN (20)

Cl thorn ClcCl2c


Humic acid + HSO5


Humic acid + SO4c




have a positive eff








HCO3 thorn SO4

cSO4


ethk HCO3thornSO4 c

frac14 16 106 M1 s1THORN (24)






View Article Online





(25)













4 Conclusions






signi

















Acknowledgements







appreciated

References



2015 284 1


2004 38 3705


Chem Eng J 2011 174 376


2014 154ndash155 36


129 153


47 2784



2015 71 10






2014 2 15836


854




2012 24 90


509


Mater 2014 270 61








View Article Online




B 2015 165 572










2009 85 171



2009 57 223


497


7 8149


2011 23 1799





Chem Eng J 2015 276 193



View Article Online


























































various catalystsa











View Article Online
















lytic performance13


2 ] (4)


+ (5)













Hthornfrac12Cat OH

(6)




follows

dC







dC BPA

dt frac14 k i

frac12Cat OHoK eq

Hthorn

thorn 1










View Article Online







k i

k PMS

frac12CatOHo












modelling studies






k t frac14 k app

K eq

Hthorn

thorn 1


(10)














for BPA


Cu2+ + HSO5

Cu+ + SO5c + H+ (11)

Cu+ + HSO5

Cu2+ + SO4c + OH (12)

Fe3+ + HSO5

Fe2+ + SO5c + H+ (13)



pH 45

018 005 0031 0002 019 607 125 022 004 0996010 0046 0001 021 485 050 023 003 0991020 013 001 095 215 015 0050 0003 0999

027 005 0043 0003 047 385 007 015 001 0998010 0062 0001 049 327 018 019 001 0985

020 017 001 083 213 008 007 001 0999036 005 0067 0001 049 459 006 015 000 0997

010 0083 0003 059 271 006 015 001 0995020 023 002 090 198 004 006 002 0996

pH 70

018 005 011 001 099 498 041 002 001 0996010 016 001 099 468 029 004 001 0999020 046 004 098 413 018 0004 0002 0999

027 005 014 001 096 418 010 0016 0002 0999010 024 001 098 403 002 003 001 0999020 053 007 091 543 010 011 002 0999

036 005 014 001 090 416 020 0043 0001 0999010 028 004 096 398 033 005 001 0999020 062 004 099 400 000 0002 0001 0999

pH 90

018 005 033 001 097 1705 037 002 001 0999010 056 001 088 1670 062 009 001 0999020 069 002 091 1288 111 024 003 0999

027 005 075 012 098 2477 060 011 007 0999010 090 008 097 1652 164 018 013 0999020 166 041 099 1314 207 017 008 0999

036 005 090 008 093 3288 132 030 008 0999010 123 004 098 1654 138 019 005 0999020 141 011 099 1371 107 076 001 0999



View Article Online



Fe2+ + HSO5

Fe3+ + SO4c + OH (14)







producing SO4c

SO5c







2k Fe2thornthornSOc

4frac14 3 108 M1 s1

(15)









intermediates

HSO5 thorn SO4

cSO5


ethk HSO5thornSO4 c

frac14 1 105 M1 s1THORN (16)

HSO5 thorn HOcSO5



(17)

HSO5 + SO5c

+ H2O SO4c + SO4

2 + O2 + H3O+ (18)

HSO5 + SO5c

+ H2O HOc + 2SO42 + O2 + 2H+ (19)










NO3 HCO3











2


8 108 M1 s1THORN (20)

Cl thorn ClcCl2c


Humic acid + HSO5


Humic acid + SO4c




have a positive eff








HCO3 thorn SO4

cSO4


ethk HCO3thornSO4 c

frac14 16 106 M1 s1THORN (24)






View Article Online





(25)













4 Conclusions






signi

















Acknowledgements







appreciated

References



2015 284 1


2004 38 3705


Chem Eng J 2011 174 376


2014 154ndash155 36


129 153


47 2784



2015 71 10






2014 2 15836


854




2012 24 90


509


Mater 2014 270 61








View Article Online




B 2015 165 572










2009 85 171



2009 57 223


497


7 8149


2011 23 1799





Chem Eng J 2015 276 193



View Article Online
















lytic performance13


2 ] (4)


+ (5)













Hthornfrac12Cat OH

(6)




follows

dC







dC BPA

dt frac14 k i

frac12Cat OHoK eq

Hthorn

thorn 1










View Article Online







k i

k PMS

frac12CatOHo












modelling studies






k t frac14 k app

K eq

Hthorn

thorn 1


(10)














for BPA


Cu2+ + HSO5

Cu+ + SO5c + H+ (11)

Cu+ + HSO5

Cu2+ + SO4c + OH (12)

Fe3+ + HSO5

Fe2+ + SO5c + H+ (13)



pH 45

018 005 0031 0002 019 607 125 022 004 0996010 0046 0001 021 485 050 023 003 0991020 013 001 095 215 015 0050 0003 0999

027 005 0043 0003 047 385 007 015 001 0998010 0062 0001 049 327 018 019 001 0985

020 017 001 083 213 008 007 001 0999036 005 0067 0001 049 459 006 015 000 0997

010 0083 0003 059 271 006 015 001 0995020 023 002 090 198 004 006 002 0996

pH 70

018 005 011 001 099 498 041 002 001 0996010 016 001 099 468 029 004 001 0999020 046 004 098 413 018 0004 0002 0999

027 005 014 001 096 418 010 0016 0002 0999010 024 001 098 403 002 003 001 0999020 053 007 091 543 010 011 002 0999

036 005 014 001 090 416 020 0043 0001 0999010 028 004 096 398 033 005 001 0999020 062 004 099 400 000 0002 0001 0999

pH 90

018 005 033 001 097 1705 037 002 001 0999010 056 001 088 1670 062 009 001 0999020 069 002 091 1288 111 024 003 0999

027 005 075 012 098 2477 060 011 007 0999010 090 008 097 1652 164 018 013 0999020 166 041 099 1314 207 017 008 0999

036 005 090 008 093 3288 132 030 008 0999010 123 004 098 1654 138 019 005 0999020 141 011 099 1371 107 076 001 0999



View Article Online



Fe2+ + HSO5

Fe3+ + SO4c + OH (14)







producing SO4c

SO5c







2k Fe2thornthornSOc

4frac14 3 108 M1 s1

(15)









intermediates

HSO5 thorn SO4

cSO5


ethk HSO5thornSO4 c

frac14 1 105 M1 s1THORN (16)

HSO5 thorn HOcSO5



(17)

HSO5 + SO5c

+ H2O SO4c + SO4

2 + O2 + H3O+ (18)

HSO5 + SO5c

+ H2O HOc + 2SO42 + O2 + 2H+ (19)










NO3 HCO3











2


8 108 M1 s1THORN (20)

Cl thorn ClcCl2c


Humic acid + HSO5


Humic acid + SO4c




have a positive eff








HCO3 thorn SO4

cSO4


ethk HCO3thornSO4 c

frac14 16 106 M1 s1THORN (24)






View Article Online





(25)













4 Conclusions






signi

















Acknowledgements







appreciated

References



2015 284 1


2004 38 3705


Chem Eng J 2011 174 376


2014 154ndash155 36


129 153


47 2784



2015 71 10






2014 2 15836


854




2012 24 90


509


Mater 2014 270 61








View Article Online




B 2015 165 572










2009 85 171



2009 57 223


497


7 8149


2011 23 1799





Chem Eng J 2015 276 193



View Article Online







k i

k PMS

frac12CatOHo












modelling studies






k t frac14 k app

K eq

Hthorn

thorn 1


(10)














for BPA


Cu2+ + HSO5

Cu+ + SO5c + H+ (11)

Cu+ + HSO5

Cu2+ + SO4c + OH (12)

Fe3+ + HSO5

Fe2+ + SO5c + H+ (13)



pH 45

018 005 0031 0002 019 607 125 022 004 0996010 0046 0001 021 485 050 023 003 0991020 013 001 095 215 015 0050 0003 0999

027 005 0043 0003 047 385 007 015 001 0998010 0062 0001 049 327 018 019 001 0985

020 017 001 083 213 008 007 001 0999036 005 0067 0001 049 459 006 015 000 0997

010 0083 0003 059 271 006 015 001 0995020 023 002 090 198 004 006 002 0996

pH 70

018 005 011 001 099 498 041 002 001 0996010 016 001 099 468 029 004 001 0999020 046 004 098 413 018 0004 0002 0999

027 005 014 001 096 418 010 0016 0002 0999010 024 001 098 403 002 003 001 0999020 053 007 091 543 010 011 002 0999

036 005 014 001 090 416 020 0043 0001 0999010 028 004 096 398 033 005 001 0999020 062 004 099 400 000 0002 0001 0999

pH 90

018 005 033 001 097 1705 037 002 001 0999010 056 001 088 1670 062 009 001 0999020 069 002 091 1288 111 024 003 0999

027 005 075 012 098 2477 060 011 007 0999010 090 008 097 1652 164 018 013 0999020 166 041 099 1314 207 017 008 0999

036 005 090 008 093 3288 132 030 008 0999010 123 004 098 1654 138 019 005 0999020 141 011 099 1371 107 076 001 0999



View Article Online



Fe2+ + HSO5

Fe3+ + SO4c + OH (14)







producing SO4c

SO5c







2k Fe2thornthornSOc

4frac14 3 108 M1 s1

(15)









intermediates

HSO5 thorn SO4

cSO5


ethk HSO5thornSO4 c

frac14 1 105 M1 s1THORN (16)

HSO5 thorn HOcSO5



(17)

HSO5 + SO5c

+ H2O SO4c + SO4

2 + O2 + H3O+ (18)

HSO5 + SO5c

+ H2O HOc + 2SO42 + O2 + 2H+ (19)










NO3 HCO3











2


8 108 M1 s1THORN (20)

Cl thorn ClcCl2c


Humic acid + HSO5


Humic acid + SO4c




have a positive eff








HCO3 thorn SO4

cSO4


ethk HCO3thornSO4 c

frac14 16 106 M1 s1THORN (24)






View Article Online





(25)













4 Conclusions






signi

















Acknowledgements







appreciated

References



2015 284 1


2004 38 3705


Chem Eng J 2011 174 376


2014 154ndash155 36


129 153


47 2784



2015 71 10






2014 2 15836


854




2012 24 90


509


Mater 2014 270 61








View Article Online




B 2015 165 572










2009 85 171



2009 57 223


497


7 8149


2011 23 1799





Chem Eng J 2015 276 193



View Article Online



Fe2+ + HSO5

Fe3+ + SO4c + OH (14)







producing SO4c

SO5c







2k Fe2thornthornSOc

4frac14 3 108 M1 s1

(15)









intermediates

HSO5 thorn SO4

cSO5


ethk HSO5thornSO4 c

frac14 1 105 M1 s1THORN (16)

HSO5 thorn HOcSO5



(17)

HSO5 + SO5c

+ H2O SO4c + SO4

2 + O2 + H3O+ (18)

HSO5 + SO5c

+ H2O HOc + 2SO42 + O2 + 2H+ (19)










NO3 HCO3











2


8 108 M1 s1THORN (20)

Cl thorn ClcCl2c


Humic acid + HSO5


Humic acid + SO4c




have a positive eff








HCO3 thorn SO4

cSO4


ethk HCO3thornSO4 c

frac14 16 106 M1 s1THORN (24)






View Article Online





(25)













4 Conclusions






signi

















Acknowledgements







appreciated

References



2015 284 1


2004 38 3705


Chem Eng J 2011 174 376


2014 154ndash155 36


129 153


47 2784



2015 71 10






2014 2 15836


854




2012 24 90


509


Mater 2014 270 61








View Article Online




B 2015 165 572










2009 85 171



2009 57 223


497


7 8149


2011 23 1799





Chem Eng J 2015 276 193



View Article Online





(25)













4 Conclusions






signi

















Acknowledgements







appreciated

References



2015 284 1


2004 38 3705


Chem Eng J 2011 174 376


2014 154ndash155 36


129 153


47 2784



2015 71 10






2014 2 15836


854




2012 24 90


509


Mater 2014 270 61








View Article Online




B 2015 165 572










2009 85 171



2009 57 223


497


7 8149


2011 23 1799





Chem Eng J 2015 276 193



View Article Online




B 2015 165 572










2009 85 171



2009 57 223


497


7 8149


2011 23 1799





Chem Eng J 2015 276 193



View Article Online

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c5ta06563A novel quasi-cubic CuFe2O4–Fe2O3 catalyst prepared at low temperature for enhanced...

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