SynergisticAdsorptionandPhotocatalyticActivityunderVisible IrradiationUsingAg-ZnO...

Research ArticleSynergistic Adsorption and Photocatalytic Activity under VisibleIrradiation Using Ag-ZnOGO Nanoparticles Derived atLow Temperature

Viet Ha Tran Thi 1 The Ha Cao 12 Tri Nhut Pham 34 Tien Thanh Pham 5

and Manh Cuong Le 6

1Masterrsquos Program in Environmental Engineering Vietnam Japan University Hanoi Vietnam2Center for Environmental Technology and Sustainable Development (CETASD) Hanoi Vietnam3Center of Excellence for Green Energy and Environmental Nanomaterials Nguyen Tat anh UniversityHo Chi Minh City Vietnam4NTT Hi-Tech Institute Nguyen Tat anh University Ho Chi Minh City Vietnam5Masterrsquos Program in Nano Technology Vietnam Japan University Hanoi Vietnam6Department of Building Materials National University of Civil Engineering Hanoi Vietnam

Correspondence should be addressed to Viet Ha Tran i ttvhavjuacvn

Received 7 March 2019 Revised 30 May 2019 Accepted 27 June 2019 Published 18 September 2019

Guest Editor Nguayen Van Noi

Copyright copy 2019 Viet Ha Tran i et al is is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work isproperly cited

Ag-ZnOgraphene oxide (AG-ZnOGO) nanocomposite was synthesized via facile aqueous solution reactions at low temperaturein order to improve the photocatalytic activity for cationic dye removal under visible light irradiation Analytical techniques werecarried out in order to determine the abilities including structure state of elements morphology and surface area of synthesizedmaterials Ag-ZnOGO nanocomposite presented an extremely high removal rate of methylene blue (MB) not only under UVlight (over 99 removal) but also under visible light (85 removal) during the same irradiation time In this study initial processparameters of catalyst dosage MB concentration and pH of the solution were also examined forMB removal efficiency effectseproposed mechanisms for the increased removal of MB by Ag-ZnOGO nanocomposite under visible irradiation include in-creased photocatalytic degradation mainly due to increased charge transfer capacity by lowering band gap energy minimizedrecombination of the excited electron-hole pairs of ZnO with the addition of Ag into the ZnO crystal lattice and an increasedadsorption capacity with the addition of GO with high surface area and semiconductor function with zero band gap energy

1 Introduction

Developing semiconductor photocatalysts has been consid-ered a promising green technology for solving environmentalissues Among various semiconductors zinc oxide (ZnO) hasbeen considered one of the most promising photocatalystsbecause of its outstanding properties such as physical andchemical stability low cost and nontoxicity us ZnO hasbeen widely used for many different applications such as inoptical materials sensors solar energy conversion devicesand photocatalysts for pollutant treatment ZnO also has

several advantages over TiO2mdashthe most popular photo-catalyst [1] which includes higher thermal stability and easierand less expensive synthesis [2] However the photocatalyticperformance of ZnO is reduced because of its wide band gap(theoreticalsim 32 eV at room temperature) [3] and high re-combination rate between photogenerated electrons from theconduction band (CB) and holes from the valence band (VB)[4] Such a noble metal modification can also influence thesurface properties in particular by introducing hydroxylgroups on the surface of the photocatalysts [5ndash7] Howeverthese modifications require calcination at high temperature

HindawiJournal of ChemistryVolume 2019 Article ID 2979517 13 pageshttpsdoiorg10115520192979517

(400ndash600degC) and the consequent need for strict control whichhinders large-scale production

Graphene sheets possess a unique two-dimensionallayered structure of sp2-hybridized carbon atoms and thusthey can exhibit novel electronic properties as zero band gapsemiconductors Ahmad et al synthesized graphene-AgZnO nanocomposite via a solvothermal method [8]However it is not easy to synthesize due to high levels ofimpurities with graphene thus oxidized forms are usuallyused as a substitute for graphene inmany research studies Inaddition graphene oxide (GO) provides a large scaffold foranchoring various substances owing to its large specificsurface area [9] and two-dimensional planar conjugatedstructure For example GO bonding with TiO2 or WO3composites has been widely investigated [10 11] MoreoverGO-based photocatalysts can avoid the aggregation ofnanoparticles anchored on graphene sheets which canprovide more reactive sites for the photocatalytic degrada-tion process For instance Nasrollahzadeh et al reported onthe synthesis and use of graphene oxideZnO nano-composite as a heterogeneous catalyst for the synthesis ofvarious tetrazoles [12] Easy separation of the GO-basedphotocatalysts used for organic removal from water systemsoffers other benefits for repeated catalyst use and wide in-dustrial applications [13 14] However most of the derivednanoparticles need to be calcinated at high temperaturethus GO can form reduced GO (rGO) or other forms of GORaj Pant et al synthesized Ag-ZnOrGO nanocomposite inan autoclave at 140degC [15] and Gao et al synthesizedsulfonated graphene oxide-ZnO-Ag photocatalyst at 300degC[13] Only limited reports are available for different fabri-cation methods of Ag-ZnOGO to treat organic pollutantsunder UV light [16]

Herein we report a novel fabrication method of Ag-ZnOGO nanocomposite and its characterizations and thenapply it for use in effective removal of the cationic dyemethylene blue (MB) in an aqueous solution is study alsoaims to save energy and costs by using a novel synthesismethod at low temperature with visible lamps rather thanUV lamps as the light source of the photocatalytic process Asuitable photocatalytic degradation mechanism for en-hanced MB removal was also proposed

2 Materials and Methods

21 Preparation of Photocatalysts Sodium hydroxide(NaOH) silver nitrate (AgNO3) zinc sulfate heptahy-drate (ZnSO4middot7H2O) ascorbic acid (C6H6O6) and MB(C16H18N3SCl) were purchased from DaeJung Chemicalsamp Metals Co Ltd Korea GO was purchased fromSigma-Aldrich Co LLC All purchased chemicals wereused without any further purification Distilled water wasused for experiments

ZnO nanoparticles were prepared by dropwise additionof 25mL of NaOH 04molL into 25mL of ZnSO4 02molLat an approximate addition rate of 5mLmin After stirringwith a magnetic stirrer (GLHPS-G Global Lab Ltd) at aspeed of 150 rpm for 60min the solution was kept at 60degCfor 2 h

e Ag-ZnO composite nanoparticles were prepared byadding 6mL of ascorbic acid 001molL and 13mL ofAgNO3 001molL into the solution of NaOH and ZnSO4while stirring under the same condition as in the first ex-periment and again the solution was kept at 70degC for 2 h

For the preparation of Ag-ZnOGO the steps of theAg-ZnO synthesis procedure were repeated At the sametime 50mg of GO was mixed into 50mL water in anultrasonicator (D250H DAIHAN Scientific Co Ltd) for30min at room temperature e two solutions were thenmixed and the final solution obtained was kept at 70degC for2 h In the last step the synthesized products were centri-fuged and washed with deionized water several times anddried in a vacuum at 70degC for 24 h

22 Characterization e synthesized reaction productswere characterized by X-ray diffraction (XRD Bruker AXSD8 ADVANCE) to identify the structure and phase com-position Wide-angle patterns were recorded from 2θ10degto 80deg using a step size of 01deg eir surface morphologiesand microstructures were examined using field emissionscanning electron microscopy (FE-SEM JEOL JSM-6500F10 kV) and transmission electron microscopy (TEM JEOLJEM-2100F) Composition mapping of the major elementson the material surface was carried out using energy dis-persive X-ray spectroscopy (EDS JEOL JSM-6500F) esurface compositions and chemical states were measured byusing X-ray photoelectron spectroscopy (XPS ermoFisher Scientific ESCALAB 250XI) e specific surfaceareas of the compounds were determined by theBrunauerndashEmmettndashTeller (BET) method using nitrogen gasadsorption Room temperature photoluminescence (PL)spectra were recorded using a fluorescence spectrometer

e visible light absorption of the synthesized productswas measured in the range of 400 to 800 nm using a UV-Visspectrophotometer (GENESYStrade 10S UV-Vis USA) withintegrating sphere accessories To plot the calibration curveof MB dye aqueous dye solutions were prepared at aconcentration ranging from 1 to 25mgL by using distilledwater e concentrations of the MB solutions were de-termined using the obtained calibration curve e dyeremoval efficiency was calculated based on followingequation

Removal efficiency() C0 minus CC0

times 100 (1)

where C0 (mgL) is the concentration of the MB solution atthe initial time t 0 (min) and C (mgL) is the concentrationafter the treatment reaction in a dark condition or after UV-visible light irradiation

23 PhotocatalyticActivityMeasurement e photocatalyticactivity of the synthesized materials was estimated by usingan illumination system consisting of five lamps [visible lamp(EFTR 20EX-D Kumho Co Ltd Republic of Korea)UVlamp (AL-2220D1 20W Alim Co Ltd the Republic ofKorea)] as irradiation sources In a typical process 20mg ofthe synthesized photocatalyst was suspended in 20mL ofMB

2 Journal of Chemistry

with a concentration of 15mgL in a cylindrical glass reactorBefore starting the photocatalytic reaction the suspensionwas stirred for 30min in a dark condition to obtain anadsorptiondesorption equilibrium between the dye and thephotocatalyst Photocatalytic reactions were carried outunder a stable condition (stirring speed of 80 rpm at in-tervals of 3 h under light irradiation)

To clarify the dominant radical or ion on the photo-catalysis reaction the experiments using different radicalscavengers were performed Scavengers including tert-butylalcohol benzoquinone ammonium oxalate and K2S2O8were used for OHbull O2

bull holes and electrons respectivelye experiment was carried out similar to the removalexperiment with the added radical scavenger (01mmol)

3 Results and Discussions

31 Characterization of Material

311 XRD Pattern Analysis Figure 1 showed the XRDpatterns of the ZnO and Ag-ZnOGO samples eAg-ZnOGO spectrum included a diffraction peak at2θ115deg of pristine GO [17 18] indicating that the majorform of graphene in the synthesized material was GO Inboth ZnO and Ag-ZnOGO spectra the observed dif-fraction peaks at 2θ 32 34 and 36deg confirmed thepresence of the hexagonal wurtzite structure of ZnO Ingeneral the intensity of the diffraction peaks decreasesgreatly with the increase in doping concentration [19]us it can be observed that the peak intensity of ZnO inthe Ag-ZnOGO sample was decreased as compared withthat of the ZnO sample Besides the XRD pattern ofAg-ZnOGO mainly showed a small silver peak at 2θ 38deg[20ndash22] and this confirmed the doping activity of Ag ontothe structure of ZnO Simultaneously a small amount ofAg entered the ZnO crystal structure as confirmed by thebroadening at 2θ 32 34 and 36deg in the Ag-ZnOGOpeaks compared to ZnO peaks [23 24] e value of fullwidth at half maximum (FWHM) of diffraction peak isshowed on Table 1

312 Morphology and Microstructure by SEM and TEMAnalysis FE-SEM and TEM analyses were used to identifythe morphology and microstructure of the synthesizedmaterialse SEM images of ZnO before addition of Ag andGO exhibited high degree of uniformity in the nanosizedZnO particles (Figures 2(a) and 2(b)) When GO was in-troduced into the composites numerous Ag-ZnO nano-particles were deposited on the GO sheets (Figures 2(c) and2(d)) In the Ag-ZnOGO heterostructure GO sheets wereconsistently decorated with Ag and ZnO nanoparticles TEMimages revealed a hexagonal shape for ZnO (Figure 2(e))with a diameter 50ndash60 nm which is in good agreement withthe diameter of ZnO revealed in SEM images Figure 2(f)shows the TEM image of Ag-ZnOGO composite dem-onstrating the attendance of few-layered GO sheets deco-rated with Ag and ZnO particles which may result in betteradsorption capacity and electron-hole separation

e chemical compositions of ZnO and Ag-ZnOGOwere analyzed by energy dispersive spectrometry (EDS) andmapping technique in conjunction with SEM (Figure 3) Allthe peaks were ascribed to Zn Ag and O in the ZnO sampleand peak of C elements appeared in the composite samplee mapping results confirmed the presence and uniformdistribution of zinc silver and oxygen on the GO surface Incombination these elemental mapping and SEM and TEMresults demonstrate the capability of GO to function as aneffective scaffold for ZnO and silver

313 XPS Analysis e surface element composition andchemical state of the as-synthesized samples were analyzedby XPS analysis as shown in Figure 4 e peaks of Zn 2p32and Zn 2p12 of the synthesized ZnO and Ag-ZnOGO wereobserved at around 10218 eV and 10451 eV respectivelywhich are very similar to the peaks of pure ZnO(Figure 4(a)) is finding therefore demonstrated thepresence of the Zn2+ form in both samples [19 25] In theC1s spectra of Ag-ZnOGO (Figure 4(b)) the presence of Cwas attributed to the GO addition Compared to ZnO the Cpeaks of the Ag-ZnOGO nanocomposite were shifted to-ward a slightly lower binding energy In the ZnO sample thepresence of C originated from the vacuum oil used in thepretreatment system before the XPS testing e four peaksin the Ag-ZnOGO sample at 2824 2848 2861 and2886 eV were ascribed to Zn-C C-CCC Zn-O-C andCO respectively [26 27]e presence of abundant carbonspecies on the surface of the Ag-ZnOGO composite in-creased the photodegradation because it facilitated the

GO

Inte

nsity

(au

)

2θ (deg)5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80

Ag

ZnOAg-ZnOGO

Figure 1 XRD patterns of the ZnO and Ag-ZnOGO samples

Table 1 FWHM in the samples

Sample FWHM (cmminus 1)ZnO 02210Ag-ZnOGO 02377

Journal of Chemistry 3

contact with organic pollutant molecules e high reso-lution spectra of the strong O1s peak (Figure 4(c)) at5313 eV in the ZnO sample was due to the oxygen in theZnO crystal lattice (Zn-O bonds) [28 29] Two O1s peaks at5315 and 5318 eV in the Ag-ZnOGO composite samplerevealed the presence of surface oxygen complexes in thecarbon phase [21 28] ese oxygen-containing groupsincreased the photocatalytic activities due to their in-volvement in the production of active radicals which play animportant role in the photodegradation process e Ag 3dXPS peaks of Ag-ZnOGO shown in Figure 4(d) located at3677 and 3740 eV were ascribed to Ag 3d52 and Ag 3d32respectively [30 31] e XPS results were in good agree-ment with the aforementioned XRD and EDS results eseobservations in Figure 4 further confirmed the successfulpreparation of Ag-ZnOGO nanoparticles and viability ofAg-ZnOGO as a superior nanocomposite material

314 UV-VIS Reflectance Spectra and Band Gap e op-tical absorption properties of the synthesized nanomaterialswere investigated by UV-VIS reflectance spectra (Figure 5)e doping activity induced a shift from the UV light

absorption of ZnO to the visible light absorption of Ag-ZnOGO e optical band gaps of the synthesized materials werecalculated by using the following Tauc equation

αh] A h] minus Eg1113872 1113873n (2)

where α is the absorption coefficient Eg is the band gap A isa constant and n is an index that characterizes the opticalabsorption process (for direct band gap semiconductormaterial n 12) By extrapolating the linear region of theplot (αh])2 vs h] the band gap could be estimatede bandgap values for ZnO and Ag-ZnOGO are given in Figure 5Band gap of Ag-ZnOGO (292 eV) is smaller than that ofsynthesized ZnO (315 eV) is decreased band gap mayhave been due to the introduction of silver and carbon asdopants in the ZnO lattice Similar phenomena have beenobserved in ZnO-based material systems in other studies[19 32 33]

315 BET Surface Area e specific surface area of thesynthesized materials was measured using the BET methodwith N2 adsorption-desorption (Figure 6) e identifiedsurface area of Ag-ZnOGO was almost 36 times larger than

(a)

(c)

(e)

(b)

(d)

(f)

Figure 2 FE-SEM and TEM analyses of synthesized materials


that of ZnO With Ag-ZnOGO present in a dark conditionpollutant adsorption is mainly assisted by the increasedspecific surface area (SBET) In general graphene has a veryhigh specific surface area [34] and thus it could provide ahigh adsorption capacity GO the oxidized form of gra-phene contains oxygen functional groups on its surface thatcan become adsorption sites erefore the enhanceddegradation capacity under visible light can be attributed tothe adsorption power of GO combined as a semiconductoror adsorption substrate [35 36] In addition the increasedpore size of Ag-ZnOGO nanocomposite could lead to theincreases in adsorption efficiency

316 PL Spectra e PL spectra of as-prepared ZnO andAg-ZnOGO at room temperature are presented in Figure 7As observed the PL intensities of the samples increase in thefollowing order Ag-ZnOGO and ZnO e PL intensity ofthe composite sample is weaker as compared with that of theZnO sample indicating that the fluorescence of the com-posite is quenched more efficiently than that of ZnO It alsoindicated that the incorporation of ZnOwith Ag and GO canimprove the separation of photoinduced electrons and holesus there is a high agreement with the order of Pl in-tensities when compared with the result from the removalexperiments and the recombination process can be

Full scale 13140 cts Cursor 0000 keV0 2 4 6 8 10

(a)


(b)

C Ka1

(c)

O Ka1

(d)

Zn Ka1

(e)

Ag La1

(f )

Figure 3 EDS and mapping analyses of synthesized materials


Zn2pZn 2p32

Zn 2p12

1015 1020 1025 1030 1035 1040 1045 1050

Inte

nsity

(au

)

Binding energy (eV)

ZnOAg-ZnOGO

(a)

C1sC-CC=C

C-OC=O

Zn-C

280 285 290 295

Inte

nsity

(au

)

Binding energy (eV)

ZnOAg-ZnOGO

(b)

O1s

525 530 535 540 545

Inte

nsity

(au

)

Binding energy (eV)

ZnOAg-ZnOGO

(c)

360 365 370 375 380

Inte

nsity

(au

)

Binding energy (eV)

Ag3dAg3d52

Ag3d32

Ag-ZnOGO

(d)

Ag-ZnOGO

Zn2p

O1s

Ag3dC1s

Inte

nsity

(au

)

Binding energy (eV)0 200 400 600 800 1000 1200

(e)

Figure 4 XPS analyses of synthesized materials


significantly suppressed through the combination of ZnOwith Ag and GO

32 Removal of MB Dye Using Synthesized Materials It iscommonly accepted that most dyes are resistant to bio-degradation and direct photolysis and many N-containingdyes such as MB undergo natural reductive anaerobicdegradation to yield potentially carcinogenic aromaticamines [31] In this study therefore MB was chosen as amodel contaminant to evaluate the photocatalytic activity ofthe synthesized photocatalysts

Figures 8(a) and 8(b) show the UV-Vis absorptionspectrum and removal efficiency of MB degraded by usingsynthesized materials under dark and light (visible and UV)irradiation conditions respectively ZnO did not showany significant adsorption of MB when the addition ofAg-ZnOGO into the MB solution without any light sourceafforded an MB removal efficiency of around 20 After theadsorption visible light or UV light was directed at the MBremoval system containing Ag-ZnOGO added into MBsolution as a photocatalyst e addition of Ag-ZnOGOinto the MB solution under visible light and UV light ir-radiation increased the MB removal efficiency after 3 h byup to 85 and 99 respectively e comparison of thelight absorption results between the dark and light irradi-ation conditions clearly demonstrated that most of the MBremoval effects were due to photocatalytic degradation bythe Ag-ZnOGO nanocomposite Under visible light MBremoval was significantly increased by Ag-ZnOGO becauseof the combination effects of the adsorption and photo-catalytic degradation Under UV conditions removal effi-ciency reached up to 99 because of the high photon energyin UV light and so photodegradation could occur morestrongly than under the visible light e photocatalyticactivity by Ag-ZnOGO under visible light is explained inthe mechanism section

To clarify the role of photogenerated radical species inthe removal process different scavengers were used It isobserved from the scavenger testsrsquo result that the degrada-tion level of MB was significantly inhibited when tert-butyl

200 300 400 500 600 700 800Wavelength (nm)

Diff

use r

efle

ctan

ce (

)

292eV

(αhυ

)2 (eV

cm

)2

315eV

Band gap (eV)25 30 35

ZnOAg-ZnOGO

(a)

Wavelength (nm)

Abso

rban

ce (a

u)

Ag-ZnOGO

ZnO

06

05

04

03

02

200 300 400 500 600 700

(b)

Figure 5 UV-VIS reflectance spectra and band gap of synthesizedmaterials

120

100

80

60

40

20

0

Relative pressure (PPo)

Qua

ntity

adso

rbed

(cm

3 g S

TP)

00 02 04 06 08 10

ZnOAg-ZnOGO

Figure 6 BET analysis data of synthesized materials

ZnO

Ag-ZnOGO

Wavelength (nm)

Inte

nsity

(au

)

350 400 450 500 550 600 650

Figure 7 PL spectra of synthesized materials


alcohol and ammonium oxalate were added us it is clearthat most of the reactive radicals responsible for catalyticactivity are found to be OHbull and photogenerated holes(Figure 9)

Synthesized composite material have higher surface areaand greater numbers of active sites as compared with ZnOwhere the photogenerated charge carriers react withabsorbed molecules to form hydroxyl and superoxide rad-icals A set of experiments was carried out in order to checkthe reusability and stability of the composite catalysts ephotodegradation experiment was duplicated eight timesafter the centrifugation and cleaning process As shown inFigure 10 the photocatalytic activities were almost stable inthe first 4 cycles From the 5th cycle the removal of MB wasdecreased it might be due to the loss of adsorption prop-erties after several centrifugation and cleaning process eparticles readily form aggregates leading to the loss of the

original structure and active sites thus decreasing thephotocatalytic efficiency

33 Effect of Initial Process Parameter pH of the solution hasbeen reported as one of the most important factors affectingthe removal efficiency of organic pollutants by photo-catalytic processes in an aqueous solution [37 38] Inter-preting the pH effects on the MB dye removal process is adifficult task because it is affected by multiple factors eeffect of pH on the removal of MB dye was investigated inthe pH range 3 to 12e pH of the point of zero charge (pHpzc) of ZnO was about 86 [39] At pH above pH pzc thesurface of the ZnO particles was mostly positively chargedAs the solution pH increases from the acidic range up to pHpzc of ZnO (pHlt 86) the decreased H3O+ concentrationproduces less repulsion of Ag-ZnOGO with the positivelycharged MB molecules resulting in increased adsorption ofMB As the solution pH further increases above pzc(pHgt 86) the increased OHminus produces more electron re-pulsion of Ag-ZnOGO with negatively charged MB mol-ecules leading to less adsorption erefore pH 85ndash9 waschosen as the optimal pH for MB adsorption (Figure 11(a))

Figure 11(b) shows the effects of different Ag-ZnOGOloadings on the MB removal process under visible lightirradiation As the dosage of Ag-ZnOGO increased up to10 gL the MB removal effect also increased e increasedAg-ZnOGO dosage led to more active sites for adsorptionand thus more moiety availability for photocatalytic deg-radation of MB molecules However even the MB removalefficiency decreased as the dosage loading was increasedabove 1 gL At higher dosages there was excessive increasein the amount of suspended Ag-ZnOGO with excessiveaddition disturbing the penetration of visible light into thereaction system is also led to reduction in the generation

12

10

08

06

04

02

00 Dark

CC 0

Light irradiation

Time (min)ndash60 ndash30 0 30 60 90 120 150 180

ZnOAg-ZnOGO_UV lightAg-ZnOGO_visible light

(a)

Abso

rban

ce (a

u)

400 500 600 700 800Wavelength (nm)

Initial MB solutionZnO_visibleAg-ZnOGOndashdark

Ag-ZnOGOndashvisibleAg-ZnOGOndashUV

(b)

Figure 8 Removal of MB by using synthesized materials

CC 0

10

08

06

04

02

00

Time (min)0 30 60 90 120 150 180

Without scavengertert-Butyl alcoholBenzoquinone

Ammonium oxalateK2S2O8

Figure 9 Evaluation of reactive radical species using variousscavengers for photocatalytic degradation of MB by usingAg-ZnOGO


of the electron-hole pairs and subsequent reduction in theproduction of oxy-radicals and hydroxyl radicals [40]Furthermore excessive photocatalyst dosage increases thepollutant removal costs Hence 1 gL was determined to bethe optimum Ag-ZnOGO dosage

Different initial MB solution concentrations rangingfrom 1mgL to 25mgL were used to evaluate the MBremoval effect by Ag-ZnOGO (Figure 11(c)) e MB re-moval efficiency decreased when the initial MB concen-tration was more than 15mgL within 3 h of irradiationWhen the MB concentration was beyond the limit of 15mgL the MB molecules adsorbed on the adsorbentphoto-catalyst surface repulsed further MB molecules fromapproaching the adsorbentphotocatalyst thereby de-creasing MB removal In addition a high initial MB con-centration hindered visible light penetration due toincreased turbidity as explained in the previous sectionwhich decreased the light irradiation effect for photocatalyticdegradation of MB [41 42]

34 PhotocatalyticMechanism reemechanisms proposedto explain the increased photocatalytic degradation of MBdye by Ag-ZnOGO under visible light irradiation areschematically shown in Figure 12

e first proposed mechanism for the increased MBremoval is associated with GO addition to the photo-catalytic system (Figure 12(a)) GO was used as a bettersubstrate for the photocatalytic reaction by increasing thesurface area of the photocatalyst Moreover the photo-catalytic degradation efficiency of MB by Ag-ZnOGOwas improved by combining it with a zero band gapsemiconductor GO [43 44] Some previous studies havereported that GO can also enhance the photocatalyticability of ZnO under visible light irradiation due to

resonance effects including the increased surface areawith added GO and increased formation of π-πlowastinteractions between the dye molecules [25] e highsurface area of GO can contribute to the effectiveadsorption of MB molecules on the photocatalyst surfaceMB is a sensitive chromophore that absorbs light in awide range of wavelengths including the visible region[45 46] and thus MB molecules easily enter an excitedstatus e electrons in the excited MBlowast can jump to theconduction band (CB) of ZnO through GO [47] and thenbe transferred to various Ag levels (Figures 12(b) and12(c)) is series of excited electron transfer can min-imize or delay the recombination of electrons with holeserefore the excited electrons can have more delayedrecombination while simultaneously increasing thecharge transfer capacity from the valence band (VB) tothe CB of ZnO

e second mechanism for the enhanced photocatalyticdegradation of MB could be due to the Ag doping effect intothe ZnO crystal lattice (Figure 12(c)) It is well known thatband gap is a region of energy with no allowed states edensity of states versus energy depends on the chemicalcomposition of the material and the state density distri-bution will be changed if the chemical composition ischanged In this case Ag dopant is the impurity so thechemical composition was changed by doping When thedoping density is high enough the dopant states generate aband If this band is very close to the valence or conductionband edge the band gap will decrease e electronstransferred to the CB of ZnO tend to be transferred to Ag atthat time which prevents delay of the recombination of theexcited electrons and holes Addition of Ag led to the for-mation of ldquostairsrdquo that allow the excited electrons to moveeasily to higher energy levels with visible light irradiationrather than directly moving down to the holes e mini-mized recombination of the excited electrons in the CB withthe holes in the VB can increase the opportunity for theproduction of oxy-radicals by reaction with O2 moleculesleading to the oxidative degradation of MB molecules

e third proposed mechanism is based on the narrowedband gap of the semiconductor (Figure 12(b)) e majorlimitation of ZnO is its restriction to UV light irradiationbecause of its wide band gap is weakness was improvedthrough Ag doping into the ZnO lattice by narrowing theband gap Dotted green lines (Figure 12(c)) represent a newband gap for ZnO which was narrowed by the interactionbetween ZnO Ag and GO during the synthesis of the Ag-ZnOGO nanocomposite [48] e major oxidative andreductive processes for the photodegradation ofMB by usingAg-ZnOGO with a narrowed band gap under visible lightillumination can be explained as shown in equation (3) to(11)

Light with appropriate spectrum + Ag-ZnOGO⟶ Ag-ZnOGO h+

+ eminus

( 1113857 (3)

CC 0

10

08

06

04

02

001st 2nd 3rd 4th 5th 6th 7th 8th

Figure 10 Reusability of the synthesized composite material


95

90

85

80

75

70

65

Deg

rada

tion

effic

ienc

y (

)

pH

35ndash

4

45ndash

5

55ndash

6

65ndash

7

75ndash

8

85ndash

9

95ndash

10

105

ndash11

115

ndash12

(a)

Dosage of catalyst (gl)

Deg

rada

tion

effic

ienc

y (

)

90

85

80

75

70

04

06

08

10

12

14

16

18

20

(b)

0 5 10 15 20 25

75

80

85

90

MB dye concentration (mgl)

Deg

rada

tion

effic

ienc

y (

)

(c)

Figure 11 Effect of the initial parameter on the MB removal efficiency

Energy (eV)

GO

MB

MBlowast

O2

ndash045eV

h+ h+ h+ h+ h+ h+

endash endash endash endash endash endash

ZnOBand gap= 33eV

Vacuum level

CB (ndash42eV)

VB (ndash75eV)

endash

endash

endash

endash

O2bullndash H2O2 OHbull

AgAg2Ag3

Agn

Ag bulkndash464eVndash360eV

Narrowed band gap

ndash442eV

(a)

(b)

(c)

Dyedyelowast + OHbullO2bull final product(s) (CO2uarr H2O)

Figure 12 Proposed mechanism for MB removal using synthesized material


(I) Oxidative reactions with holes

h++ H2O⟶ H+

+ OHbull(4)

2h++ 2H2O⟶ 2H+

+ H2O2 (5)

H2O2⟶ HObull+

bullOH (6)

(II) Reduction reaction with O2

2eminus+ O2⟶

bullO2minus

(7)

bullO2minus

+ 2H+⟶ H2O2 + O2 (8)

H2O2⟶ HObull+

bullOH (9)

(III) Photocatalytic oxidation with oxy-radicals

DyeDyelowast +bullOH⟶ final products CO2H2O ( 1113857

(10)

DyeDyelowast +bullO2

minus ⟶ final products CO2H2O ( 1113857

(11)

35 Energy and Cost Issue Nowadays the demand andmarket for the use of nanoparticles or nanocatalysts inpollutant removal are increasing As discussed above ZnOnanoparticle is one of the most promising materials forwastewater treatment Performance of ZnO can be enhancedby adding some ingredients to make better nanocompositee methods currently developed for making better ZnOnanomaterials mainly consist of sol-gel template and hy-drothermal methods However the requirement of highcrystallinity is a major problem in ZnO synthesis With the

sol-gel method calcination of gels or thermal annealing ofemulsions is therefore required to induce crystallization ofthe nanoparticle and thus normally a high temperature ofmore than 200degC is required Hydrothermal methods aredirectly carried out at slightly lower temperatures than sol-gel methods (but not less than 120degC) However nano-crystals formed with hydrothermal methods agglomerateand thus are insoluble in most solvents and thus somestabilizing agents are required to prevent agglomerationeir characteristics from previous relevant study outcomesare summarized in Table 2 with comparisons

e search for a simple and economic synthesis methodto derive nanoparticles with good size and shape at lowtemperature is still an open challenge e ability to producenanomaterials at lower temperatures is needed for thepurpose of saving energy and increasing safety for large-scaleproduction In this study we demonstrate that it is possibleto cost effectively produce nanomaterials at low temperaturein considerable quantities with increased safety in a widerange of applications By adding the noble metal Ag as adopant and GO as a high surface area adsorption substratefirstly our nanomaterial can work excellently for adsorptionand also as a photocatalyst even under visible light Re-searchers have previously used UV light in their studies toirradiate the photocatalyst and the removal efficiency oftheir process was very high However the price of a UV lampis at least two times as high as the price of a visible lampFurthermore UV waves are invisible but very harmful forhuman eyes Secondly for processing our current methodonly a calcination temperature of around 70degC is neededwithout any requirements for complex instruments Froman economical view such fabrication may offer better op-portunities to significantly lower the cost of manufacturingnanomaterials while bringing environmental advantagessuch as low energy consumption and reduced CO2 emis-sions irdly the simplicity of the synthesis procedure

Table 2 Comparison between previous and current studies for MB removal using photocatalytic degradation

Photocatalyst Chemical ingredients Calcinationtemperature

Lightsource Adsorption Photocatalysis Total

removal Remark Ref

SulphonatedGO-ZnO-Ag

Zn(CH3COO)22H2OHMTA EG AGNO3 HClClCH2CH2SO3H AgNO3NaNO3 KMnO4 H2O2

H2SO4

160 Visible 20 78 98Sulfonated GO high

calcinationtemperature

[13]

Ag-ZnORGO

GO bis-hexamethylenetriamine Zn(NO3)26H2O

AgNO3 ethanol

140 inautoclave Visible Not separated 65

Reduced GO highcalcination

temperature inautoclave

[15]

Graphene-AgZnO

Graphene EG CH3COOAgZn(CH3COO)22H2O

NaOH160 Visible 286 656 944

Graphene expensivehigh calcinationtemperature

[8]

AgZnOGO Graphite oxide ZnOAgNO3

55 UV Not separated 98 GO UV light highenergy safety issue [16]

Ag-ZnOGO Graphene oxide AgNO3ZnSO47H2O C6H6O6

70Visible 25 60 85 GO visible light low

energy high safetyisstudy

UV 25 74 99 UV light high energysafety issue

isstudy


would make it safe for workers and easy to apply to in-dustrial manufacturing

4 Conclusion

Ag-ZnOGO nanocomposite was successfully synthesizedby facile aqueous solution reactions at low temperature eMB removal efficiency increased up to 99 under the UVlight and 85 under visible light e optimum conditionsfor maximum removal efficiency of MB were pH 85ndash9temperature 35degC and dosage 1 gL at MB concentration15mgL e significant increase in photocatalytic degra-dation for MB removal exhibited by Ag-ZnOGO was due tothe combined effects of the two semiconductors ZnO andGO and Ag doping into the ZnO crystal lattice e pro-posed mechanism for enhanced removal includes an in-crease in adsorption by adding GO with a high surface areaand an increase in photocatalytic activities due to improvedcharge transfer capacity achieved through lowering the bandgap energy of ZnO thus minimizing the recombination ofthe excited electrons in the CB with the holes in VB of ZnOleading to higher removal rate of MB

Data Availability

e data used to support the findings of this study areavailable from the corresponding author upon request

Conflicts of Interest

e authors declare that they have no conflicts of interest

Acknowledgments

e authors would like to thank Vietnam Japan UniversityResearch Fund which is funded by Japan InternationalCooperation Agency (JICA) to full time lecturer of VietnamJapan University (Dr Trani Viet Ha of Masterrsquos Programof Vietnam Japan University)

References

[1] M Nasrollahzadeh M Atarod B Jaleh andM Gandomirouzbahani ldquoIn situ green synthesis of Agnanoparticles on graphene oxideTiO2 nanocomposite andtheir catalytic activity for the reduction of 4-nitrophenol congored and methylene bluerdquo Ceramics International vol 42 no 7pp 8587ndash8596 2016

[2] M Eskandari V Ahmadi S Kohnehpoushi and M Yousefirad ldquoImprovement of ZnO nanorod based quantum Dot(cadmium sulfide) sensitized solar cell efficiency by aluminumdopingrdquo Physica E Low-Dimensional Systems and Nano-structures vol 66 pp 275ndash282 2015

[3] K Takahashi A Yoshikawa and S Adarsh Wide BandgapSemiconductors Fundamental Properties andModern Photonicand Electronic Devices Springer Heidelberg Germany 2007

[4] F Ghorbani Shahna A Bahrami I Alimohammadi et alldquoChlorobenzene degeradation by non-thermal plasma com-bined with EG-TiO2ZnO as a photocatalyst effect of pho-tocatalyst on CO2 selectivity and byproducts reductionrdquoJournal of Hazardous Materials vol 324 pp 544ndash553 2017

[5] X Li Q Wang Y Zhao W Wu J Chen and H MengldquoGreen synthesis and photo-catalytic performances for ZnO-reduced graphene oxide nanocompositesrdquo Journal of Colloidand Interface Science vol 411 pp 69ndash75 2013

[6] O Yayapao T ongtem A Phuruangrat and S ongtemldquoSonochemical synthesis of Dy-doped ZnO nanostructuresand their photocatalytic propertiesrdquo Journal of Alloys andCompounds vol 576 pp 72ndash79 2013

[7] L Zhang N Li H Jiu G Qi and Y Huang ldquoZnO-reducedgraphene oxide nanocomposites as efficient photocatalysts forphotocatalytic reduction of CO2rdquo Ceramics Internationalvol 41 no 5 pp 6256ndash6262 2015

[8] M Ahmad E Ahmed Z L Hong N R Khalid W Ahmedand A Elhissi ldquoGraphene-AgZnO nanocomposites as highperformance photocatalysts under visible light irradiationrdquoJournal of Alloys and Compounds vol 577 pp 717ndash727 2013

[9] A Omidvar B Jaleh M Nasrollahzadeh and H R DasmehldquoFabrication characterization and application of GOFe3O4Pdnanocomposite as a magnetically separable and reusable cat-alyst for the reduction of organic dyesrdquo Chemical EngineeringResearch and Design vol 121 pp 339ndash347 2017

[10] L-L Tan W-J Ong S-P Chai and A Mohamed ldquoReducedgraphene oxide-TiO2 nanocomposite as a promising visible-light-active photocatalyst for the conversion of carbon di-oxiderdquo Nanoscale Research Letters vol 8 no 1 pp 1ndash9 2013

[11] P-Q Wang Y Bai P-Y Luo and J-Y Liu ldquoGraphene-WO3nanobelt composite elevated conduction band toward pho-tocatalytic reduction of CO2 into hydrocarbon fuelsrdquo Ca-talysis Communications vol 38 pp 82ndash85 2013

[12] M Nasrollahzadeh B Jaleh and A Jabbari ldquoSynthesis charac-terization and catalytic activity of graphene oxideZnO nano-compositesrdquoRSCAdvances vol 4 no 69 pp 36713ndash36720 2014

[13] P Gao K Ng and D D Sun ldquoSulfonated graphene oxide-ZnO-Ag photocatalyst for fast photodegradation and disin-fection under visible lightrdquo Journal of Hazardous Materialsvol 262 pp 826ndash835 2013

[14] B Jaleh and A Jabbari ldquoEvaluation of reduced grapheneoxideZnO effect on properties of PVDF nanocompositefilmsrdquo Applied Surface Science vol 320 pp 339ndash347 2014

[15] H Raj Pant B Pant H Joo Kim et al ldquoA green and facile one-pot synthesis of Ag-ZnORGO nanocomposite with effectivephotocatalytic activity for removal of organic pollutantsrdquoCeramics International vol 39 no 5 pp 5083ndash5091 2013

[16] J Qin R Li C Lu Y Jiang H Tang and X Yang ldquoAgZnOgraphene oxide heterostructure for the removal of rhodamineB by the synergistic adsorption-degradation effectsrdquo CeramicsInternational vol 41 no 3 pp 4231ndash4237 2015

[17] S Xu L Fu T S H Pham A Yu F Han and L ChenldquoPreparation of ZnO flowerreduced graphene oxide compositewith enhanced photocatalytic performance under sunlightrdquo Ce-ramics International vol 41 no 3 pp 4007ndash4013 2015

[18] L Zhang G Du B Zhou and L Wang ldquoGreen synthesis offlower-like ZnO decorated reduced graphene oxide compos-itesrdquo Ceramics International vol 40 no 1 pp 1241ndash1244 2014

[19] S Shet K-S Ahn T Deutsch et al ldquoSynthesis and charac-terization of band gap-reduced ZnON and ZnO(Al N) filmsfor photoelectrochemical water splittingrdquo Journal of MaterialsResearch vol 25 no 1 pp 69ndash75 2010

[20] R S Patil M R Kokate D V Shinde S S Kolekar andS H Han ldquoSynthesis and enhancement of photocatalyticactivities of ZnO by silver nanoparticlesrdquo Spectrochimica ActaPart A Molecular and Biomolecular Spectroscopy vol 122pp 113ndash117 2014


[21] Z H Ibupoto N Jamal K Khun X Liu andMWillander ldquoApotentiometric immunosensor based on silver nanoparticlesdecorated ZnO nanotubes for the selective detection ofd-dimerrdquo Sensors and Actuators B Chemical vol 182pp 104ndash111 2013

[22] Y-W Tseng F-Y Hung T-S Lui and S-J ChangldquoStructural and Raman properties of silver-doped ZnOnanorod arrays using electrically induced crystallizationprocessrdquo Materials Research Bulletin vol 64 pp 274ndash2782015

[23] R Viswanath H S B Naik Y K G SomalanaikP K P Neelanjeneallu K N Harish and M C PrabhakaraldquoStudies on characterization optical absorption and photo-luminescence of yttrium doped ZnS nanoparticlesrdquo Journal ofNanotechnology vol 2014 Article ID 924797 8 pages 2014

[24] S W Lu B I Lee Z L Wang et al ldquoSynthesis and pho-toluminescence enhancement of Mn2+-doped ZnS nano-crystalsrdquo Journal of Luminescence vol 92 no 1-2 pp 73ndash782000

[25] S Vadivel M Vanitha A Muthukrishnaraj andN Balasubramanian ldquoGraphene oxidendashBiOBr compositematerial as highly efficient photocatalyst for degradation ofmethylene blue and rhodamine-B dyesrdquo Journal of WaterProcess Engineering vol 1 pp 17ndash26 2014

[26] H Ma X Cheng C Ma et al ldquoCharacterization and pho-tocatalytic activity of N-doped ZnOZnS compositesrdquo In-ternational Journal of Photoenergy vol 2013 Article ID625024 8 pages 2013

[27] M Ahmad E Ahmed W Ahmed A Elhissi Z L Hong andR N Khalid ldquoEnhancing visible light responsive photo-catalytic activity by decorating Mn-doped ZnO nanoparticleson graphenerdquo Ceramics International vol 40 no 7pp 10085ndash10097 2014

[28] K Dai L Lu C Liang et al ldquoGraphene oxide modified ZnOnanorods hybrid with high reusable photocatalytic activityunder UV-LED irradiationrdquoMaterials Chemistry and Physicsvol 143 no 3 pp 1410ndash1416 2014

[29] Y Ji S-A Lee A-N Cha et al ldquoResistive switching char-acteristics of ZnO-graphene quantum dots and their use as anactive component of an organic memory cell with one diode-one resistor architecturerdquo Organic Electronics vol 18pp 77ndash83 2015

[30] J Xu Y Chang Y Zhang S Ma Y Qu and C Xu ldquoEffect ofsilver ions on the structure of ZnO and photocatalytic per-formance of AgZnO compositesrdquo Applied Surface Sciencevol 255 no 5 pp 1996ndash1999 2008

[31] J Xu X Han H Liu and Y Hu ldquoSynthesis and opticalproperties of silver nanoparticles stabilized by gemini sur-factantrdquo Colloids and Surfaces A Physicochemical and En-gineering Aspects vol 273 no 1ndash3 pp 179ndash183 2006

[32] B Sankara Reddy Y Prabhakara Reddy S V Reddy andN K Reddy ldquoStructural optical and magnetic properties of(Fe Ag) co-doped ZnO nanostructuresrdquo Advanced MaterialsLetters vol 5 pp 199ndash205 2014

[33] R Rahimi J Shokrayian and M Rabbani ldquoPhotocatalyticremoving of methylene blue by using of Cu-doped ZnO Ag-doped ZnO and CuAg-codoped ZnO nanostructurerdquo inProceedings of the 17th International Electronic Conference onSynthetic Organic Chemistry Basel Switzerland November2013

[34] Y Zhu S Murali W Cai et al ldquoGraphene and grapheneoxide synthesis properties and applicationsrdquo AdvancedMaterials vol 22 no 35 pp 3906ndash3924 2010

[35] P Fu Y Luan and X Dai ldquoPreparation of activated carbonfibers supported TiO2 photocatalyst and evaluation of itsphotocatalytic reactivityrdquo Journal of Molecular Catalysis AChemical vol 221 no 1-2 pp 81ndash88 2004

[36] H Yoneyama and T Torimoto ldquoTitanium dioxideadsorbenthybrid photocatalysts for photodestruction of organic sub-stances of dilute concentrationsrdquo Catalysis Today vol 58no 2-3 pp 133ndash140 2000

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

[38] L N Lewis ldquoChemical catalysis by colloids and clustersrdquoChemical Reviews vol 93 no 8 pp 2693ndash2730 1993

[39] J Wang Z Jiang Z Zhang et al ldquoSonocatalytic degradationof acid red B and rhodamine B catalyzed by nano-sized ZnOpowder under ultrasonic irradiationrdquo Ultrasonics Sono-chemistry vol 15 no 5 pp 768ndash774 2008

[40] M Pera-Titus V Garcıa-Molina M A Bantildeos J Gimenezand S Esplugas ldquoDegradation of chlorophenols by means ofadvanced oxidation processes a general reviewrdquo AppliedCatalysis B Environmental vol 47 no 4 pp 219ndash256 2004

[41] M M Ba-Abbad A A Al-Amiery A Mohamad andM Takriff ldquoToxicity evaluation for low concentration ofchlorophenols under solar radiation using zinc oxide (ZnO)nanoparticlesrdquo International Journal of Physical Sciencesvol 7 no 1 pp 48ndash52 2012

[42] M M Ba-Abbad A A H Kadhum A Bakar MohamadM S Takriff and K Sopian ldquoe effect of process parameterson the size of ZnO nanoparticles synthesized via the sol-geltechniquerdquo Journal of Alloys and Compounds vol 550pp 63ndash70 2013

[43] S Cao K L Yeung J K C Kwan P M T To and S C T YuldquoAn investigation of the performance of catalytic aerogelfiltersrdquo Applied Catalysis B Environmental vol 86 no 3-4pp 127ndash136 2009

[44] N Yao S Cao and K L Yeung ldquoMesoporous TiO2-SiO2aerogels with hierarchal pore structuresrdquo Microporous andMesoporous Materials vol 117 no 3 pp 570ndash579 2009

[45] J S Lee K H You and C B Park ldquoHighly photoactive lowbandgap TiO2 nanoparticles wrapped by graphenerdquoAdvancedMaterials vol 24 no 8 pp 1084ndash1088 2012

[46] A Sionkowska ldquoe influence of methylene blue on thephotochemical stability of collagenrdquo Polymer Degradationand Stability vol 67 no 1 pp 79ndash83 2000

[47] A Adan-Mas and D Wei ldquoPhotoelectrochemical propertiesof graphene and its derivativesrdquo Nanomaterials vol 3 no 3pp 325ndash356 2013

[48] H N Tien V H Luan L T Hoa et al ldquoOne-pot synthesis of areduced graphene oxide-zinc oxide sphere composite and itsuse as a visible light photocatalystrdquo Chemical EngineeringJournal vol 229 pp 126ndash133 2013


TribologyAdvances in

Hindawiwwwhindawicom Volume 2018


International Journal ofInternational Journal ofPhotoenergy


Journal of

Chemistry


Advances inPhysical Chemistry

Hindawiwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2018

Bioinorganic Chemistry and ApplicationsHindawiwwwhindawicom Volume 2018

SpectroscopyInternational Journal of


Hindawi Publishing Corporation httpwwwhindawicom Volume 2013Hindawiwwwhindawicom

The Scientific World Journal

Volume 2018

Medicinal ChemistryInternational Journal of


NanotechnologyHindawiwwwhindawicom Volume 2018

Journal of

Applied ChemistryJournal of



Biochemistry Research International


Enzyme Research


Journal of

SpectroscopyAnalytical ChemistryInternational Journal of


MaterialsJournal of



BioMed Research International Electrochemistry

International Journal of


Na

nom

ate

ria

ls


Journal ofNanomaterials

Submit your manuscripts atwwwhindawicom

(400ndash600degC) and the consequent need for strict control whichhinders large-scale production

Graphene sheets possess a unique two-dimensionallayered structure of sp2-hybridized carbon atoms and thusthey can exhibit novel electronic properties as zero band gapsemiconductors Ahmad et al synthesized graphene-AgZnO nanocomposite via a solvothermal method [8]However it is not easy to synthesize due to high levels ofimpurities with graphene thus oxidized forms are usuallyused as a substitute for graphene inmany research studies Inaddition graphene oxide (GO) provides a large scaffold foranchoring various substances owing to its large specificsurface area [9] and two-dimensional planar conjugatedstructure For example GO bonding with TiO2 or WO3composites has been widely investigated [10 11] MoreoverGO-based photocatalysts can avoid the aggregation ofnanoparticles anchored on graphene sheets which canprovide more reactive sites for the photocatalytic degrada-tion process For instance Nasrollahzadeh et al reported onthe synthesis and use of graphene oxideZnO nano-composite as a heterogeneous catalyst for the synthesis ofvarious tetrazoles [12] Easy separation of the GO-basedphotocatalysts used for organic removal from water systemsoffers other benefits for repeated catalyst use and wide in-dustrial applications [13 14] However most of the derivednanoparticles need to be calcinated at high temperaturethus GO can form reduced GO (rGO) or other forms of GORaj Pant et al synthesized Ag-ZnOrGO nanocomposite inan autoclave at 140degC [15] and Gao et al synthesizedsulfonated graphene oxide-ZnO-Ag photocatalyst at 300degC[13] Only limited reports are available for different fabri-cation methods of Ag-ZnOGO to treat organic pollutantsunder UV light [16]

Herein we report a novel fabrication method of Ag-ZnOGO nanocomposite and its characterizations and thenapply it for use in effective removal of the cationic dyemethylene blue (MB) in an aqueous solution is study alsoaims to save energy and costs by using a novel synthesismethod at low temperature with visible lamps rather thanUV lamps as the light source of the photocatalytic process Asuitable photocatalytic degradation mechanism for en-hanced MB removal was also proposed

2 Materials and Methods

21 Preparation of Photocatalysts Sodium hydroxide(NaOH) silver nitrate (AgNO3) zinc sulfate heptahy-drate (ZnSO4middot7H2O) ascorbic acid (C6H6O6) and MB(C16H18N3SCl) were purchased from DaeJung Chemicalsamp Metals Co Ltd Korea GO was purchased fromSigma-Aldrich Co LLC All purchased chemicals wereused without any further purification Distilled water wasused for experiments

ZnO nanoparticles were prepared by dropwise additionof 25mL of NaOH 04molL into 25mL of ZnSO4 02molLat an approximate addition rate of 5mLmin After stirringwith a magnetic stirrer (GLHPS-G Global Lab Ltd) at aspeed of 150 rpm for 60min the solution was kept at 60degCfor 2 h

e Ag-ZnO composite nanoparticles were prepared byadding 6mL of ascorbic acid 001molL and 13mL ofAgNO3 001molL into the solution of NaOH and ZnSO4while stirring under the same condition as in the first ex-periment and again the solution was kept at 70degC for 2 h

For the preparation of Ag-ZnOGO the steps of theAg-ZnO synthesis procedure were repeated At the sametime 50mg of GO was mixed into 50mL water in anultrasonicator (D250H DAIHAN Scientific Co Ltd) for30min at room temperature e two solutions were thenmixed and the final solution obtained was kept at 70degC for2 h In the last step the synthesized products were centri-fuged and washed with deionized water several times anddried in a vacuum at 70degC for 24 h

22 Characterization e synthesized reaction productswere characterized by X-ray diffraction (XRD Bruker AXSD8 ADVANCE) to identify the structure and phase com-position Wide-angle patterns were recorded from 2θ10degto 80deg using a step size of 01deg eir surface morphologiesand microstructures were examined using field emissionscanning electron microscopy (FE-SEM JEOL JSM-6500F10 kV) and transmission electron microscopy (TEM JEOLJEM-2100F) Composition mapping of the major elementson the material surface was carried out using energy dis-persive X-ray spectroscopy (EDS JEOL JSM-6500F) esurface compositions and chemical states were measured byusing X-ray photoelectron spectroscopy (XPS ermoFisher Scientific ESCALAB 250XI) e specific surfaceareas of the compounds were determined by theBrunauerndashEmmettndashTeller (BET) method using nitrogen gasadsorption Room temperature photoluminescence (PL)spectra were recorded using a fluorescence spectrometer

e visible light absorption of the synthesized productswas measured in the range of 400 to 800 nm using a UV-Visspectrophotometer (GENESYStrade 10S UV-Vis USA) withintegrating sphere accessories To plot the calibration curveof MB dye aqueous dye solutions were prepared at aconcentration ranging from 1 to 25mgL by using distilledwater e concentrations of the MB solutions were de-termined using the obtained calibration curve e dyeremoval efficiency was calculated based on followingequation

Removal efficiency() C0 minus CC0

times 100 (1)

where C0 (mgL) is the concentration of the MB solution atthe initial time t 0 (min) and C (mgL) is the concentrationafter the treatment reaction in a dark condition or after UV-visible light irradiation

23 PhotocatalyticActivityMeasurement e photocatalyticactivity of the synthesized materials was estimated by usingan illumination system consisting of five lamps [visible lamp(EFTR 20EX-D Kumho Co Ltd Republic of Korea)UVlamp (AL-2220D1 20W Alim Co Ltd the Republic ofKorea)] as irradiation sources In a typical process 20mg ofthe synthesized photocatalyst was suspended in 20mL ofMB











GO

Inte

nsity

(au

)

2θ (deg)5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80

Ag

ZnOAg-ZnOGO








αh] A h] minus Eg1113872 1113873n (2)



(a)

(c)

(e)

(b)

(d)

(f)






(a)


(b)

C Ka1

(c)

O Ka1

(d)

Zn Ka1

(e)

Ag La1

(f )



Zn2pZn 2p32

Zn 2p12

1015 1020 1025 1030 1035 1040 1045 1050

Inte

nsity

(au

)

Binding energy (eV)

ZnOAg-ZnOGO

(a)

C1sC-CC=C

C-OC=O

Zn-C

280 285 290 295

Inte

nsity

(au

)

Binding energy (eV)

ZnOAg-ZnOGO

(b)

O1s

525 530 535 540 545

Inte

nsity

(au

)

Binding energy (eV)

ZnOAg-ZnOGO

(c)

360 365 370 375 380

Inte

nsity

(au

)

Binding energy (eV)

Ag3dAg3d52

Ag3d32

Ag-ZnOGO

(d)

Ag-ZnOGO

Zn2p

O1s

Ag3dC1s

Inte

nsity

(au

)


(e)







200 300 400 500 600 700 800Wavelength (nm)

Diff

use r

efle

ctan

ce (

)

292eV

(αhυ

)2 (eV

cm

)2

315eV


ZnOAg-ZnOGO

(a)

Wavelength (nm)

Abso

rban

ce (a

u)

Ag-ZnOGO

ZnO

06

05

04

03

02

200 300 400 500 600 700

(b)


120

100

80

60

40

20

0


Qua

ntity

adso

rbed

(cm

3 g S

TP)

00 02 04 06 08 10

ZnOAg-ZnOGO


ZnO

Ag-ZnOGO

Wavelength (nm)

Inte

nsity

(au

)

350 400 450 500 550 600 650








12

10

08

06

04

02

00 Dark

CC 0

Light irradiation



(a)

Abso

rban

ce (a

u)

400 500 600 700 800Wavelength (nm)



(b)


CC 0

10

08

06

04

02

00

Time (min)0 30 60 90 120 150 180













+ eminus

( 1113857 (3)

CC 0

10

08

06

04

02




95

90

85

80

75

70

65

Deg

rada

tion

effic

ienc

y (

)

pH

35ndash

4

45ndash

5

55ndash

6

65ndash

7

75ndash

8

85ndash

9

95ndash

10

105

ndash11

115

ndash12

(a)


Deg

rada

tion

effic

ienc

y (

)

90

85

80

75

70

04

06

08

10

12

14

16

18

20

(b)

0 5 10 15 20 25

75

80

85

90


Deg

rada

tion

effic

ienc

y (

)

(c)


Energy (eV)

GO

MB

MBlowast

O2

ndash045eV

h+ h+ h+ h+ h+ h+


ZnOBand gap= 33eV

Vacuum level

CB (ndash42eV)

VB (ndash75eV)

endash

endash

endash

endash


AgAg2Ag3

Agn


Narrowed band gap

ndash442eV

(a)

(b)

(c)





h++ H2O⟶ H+

+ OHbull(4)

2h++ 2H2O⟶ 2H+

+ H2O2 (5)

H2O2⟶ HObull+

bullOH (6)


2eminus+ O2⟶

bullO2minus

(7)

bullO2minus

+ 2H+⟶ H2O2 + O2 (8)

H2O2⟶ HObull+

bullOH (9)



(10)



(11)







removal Remark Ref



H2SO4



[13]

Ag-ZnORGO


AgNO3 ethanol




[15]

Graphene-AgZnO




[8]







isstudy



4 Conclusion


Data Availability




Acknowledgments


References
























































Journal of

Chemistry





Journal of

Volume 2018






Volume 2018




Journal of






Enzyme Research


Journal of



MaterialsJournal of






Na

nom

ate

ria

ls













GO

Inte

nsity

(au

)

2θ (deg)5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80

Ag

ZnOAg-ZnOGO








αh] A h] minus Eg1113872 1113873n (2)



(a)

(c)

(e)

(b)

(d)

(f)






(a)


(b)

C Ka1

(c)

O Ka1

(d)

Zn Ka1

(e)

Ag La1

(f )



Zn2pZn 2p32

Zn 2p12

1015 1020 1025 1030 1035 1040 1045 1050

Inte

nsity

(au

)

Binding energy (eV)

ZnOAg-ZnOGO

(a)

C1sC-CC=C

C-OC=O

Zn-C

280 285 290 295

Inte

nsity

(au

)

Binding energy (eV)

ZnOAg-ZnOGO

(b)

O1s

525 530 535 540 545

Inte

nsity

(au

)

Binding energy (eV)

ZnOAg-ZnOGO

(c)

360 365 370 375 380

Inte

nsity

(au

)

Binding energy (eV)

Ag3dAg3d52

Ag3d32

Ag-ZnOGO

(d)

Ag-ZnOGO

Zn2p

O1s

Ag3dC1s

Inte

nsity

(au

)


(e)







200 300 400 500 600 700 800Wavelength (nm)

Diff

use r

efle

ctan

ce (

)

292eV

(αhυ

)2 (eV

cm

)2

315eV


ZnOAg-ZnOGO

(a)

Wavelength (nm)

Abso

rban

ce (a

u)

Ag-ZnOGO

ZnO

06

05

04

03

02

200 300 400 500 600 700

(b)


120

100

80

60

40

20

0


Qua

ntity

adso

rbed

(cm

3 g S

TP)

00 02 04 06 08 10

ZnOAg-ZnOGO


ZnO

Ag-ZnOGO

Wavelength (nm)

Inte

nsity

(au

)

350 400 450 500 550 600 650








12

10

08

06

04

02

00 Dark

CC 0

Light irradiation



(a)

Abso

rban

ce (a

u)

400 500 600 700 800Wavelength (nm)



(b)


CC 0

10

08

06

04

02

00

Time (min)0 30 60 90 120 150 180













+ eminus

( 1113857 (3)

CC 0

10

08

06

04

02




95

90

85

80

75

70

65

Deg

rada

tion

effic

ienc

y (

)

pH

35ndash

4

45ndash

5

55ndash

6

65ndash

7

75ndash

8

85ndash

9

95ndash

10

105

ndash11

115

ndash12

(a)


Deg

rada

tion

effic

ienc

y (

)

90

85

80

75

70

04

06

08

10

12

14

16

18

20

(b)

0 5 10 15 20 25

75

80

85

90


Deg

rada

tion

effic

ienc

y (

)

(c)


Energy (eV)

GO

MB

MBlowast

O2

ndash045eV

h+ h+ h+ h+ h+ h+


ZnOBand gap= 33eV

Vacuum level

CB (ndash42eV)

VB (ndash75eV)

endash

endash

endash

endash


AgAg2Ag3

Agn


Narrowed band gap

ndash442eV

(a)

(b)

(c)





h++ H2O⟶ H+

+ OHbull(4)

2h++ 2H2O⟶ 2H+

+ H2O2 (5)

H2O2⟶ HObull+

bullOH (6)


2eminus+ O2⟶

bullO2minus

(7)

bullO2minus

+ 2H+⟶ H2O2 + O2 (8)

H2O2⟶ HObull+

bullOH (9)



(10)



(11)







removal Remark Ref



H2SO4



[13]

Ag-ZnORGO


AgNO3 ethanol




[15]

Graphene-AgZnO




[8]







isstudy



4 Conclusion


Data Availability




Acknowledgments


References
























































Journal of

Chemistry





Journal of

Volume 2018






Volume 2018




Journal of






Enzyme Research


Journal of



MaterialsJournal of






Na

nom

ate

ria

ls







αh] A h] minus Eg1113872 1113873n (2)



(a)

(c)

(e)

(b)

(d)

(f)






(a)


(b)

C Ka1

(c)

O Ka1

(d)

Zn Ka1

(e)

Ag La1

(f )



Zn2pZn 2p32

Zn 2p12

1015 1020 1025 1030 1035 1040 1045 1050

Inte

nsity

(au

)

Binding energy (eV)

ZnOAg-ZnOGO

(a)

C1sC-CC=C

C-OC=O

Zn-C

280 285 290 295

Inte

nsity

(au

)

Binding energy (eV)

ZnOAg-ZnOGO

(b)

O1s

525 530 535 540 545

Inte

nsity

(au

)

Binding energy (eV)

ZnOAg-ZnOGO

(c)

360 365 370 375 380

Inte

nsity

(au

)

Binding energy (eV)

Ag3dAg3d52

Ag3d32

Ag-ZnOGO

(d)

Ag-ZnOGO

Zn2p

O1s

Ag3dC1s

Inte

nsity

(au

)


(e)







200 300 400 500 600 700 800Wavelength (nm)

Diff

use r

efle

ctan

ce (

)

292eV

(αhυ

)2 (eV

cm

)2

315eV


ZnOAg-ZnOGO

(a)

Wavelength (nm)

Abso

rban

ce (a

u)

Ag-ZnOGO

ZnO

06

05

04

03

02

200 300 400 500 600 700

(b)


120

100

80

60

40

20

0


Qua

ntity

adso

rbed

(cm

3 g S

TP)

00 02 04 06 08 10

ZnOAg-ZnOGO


ZnO

Ag-ZnOGO

Wavelength (nm)

Inte

nsity

(au

)

350 400 450 500 550 600 650








12

10

08

06

04

02

00 Dark

CC 0

Light irradiation



(a)

Abso

rban

ce (a

u)

400 500 600 700 800Wavelength (nm)



(b)


CC 0

10

08

06

04

02

00

Time (min)0 30 60 90 120 150 180













+ eminus

( 1113857 (3)

CC 0

10

08

06

04

02




95

90

85

80

75

70

65

Deg

rada

tion

effic

ienc

y (

)

pH

35ndash

4

45ndash

5

55ndash

6

65ndash

7

75ndash

8

85ndash

9

95ndash

10

105

ndash11

115

ndash12

(a)


Deg

rada

tion

effic

ienc

y (

)

90

85

80

75

70

04

06

08

10

12

14

16

18

20

(b)

0 5 10 15 20 25

75

80

85

90


Deg

rada

tion

effic

ienc

y (

)

(c)


Energy (eV)

GO

MB

MBlowast

O2

ndash045eV

h+ h+ h+ h+ h+ h+


ZnOBand gap= 33eV

Vacuum level

CB (ndash42eV)

VB (ndash75eV)

endash

endash

endash

endash


AgAg2Ag3

Agn


Narrowed band gap

ndash442eV

(a)

(b)

(c)





h++ H2O⟶ H+

+ OHbull(4)

2h++ 2H2O⟶ 2H+

+ H2O2 (5)

H2O2⟶ HObull+

bullOH (6)


2eminus+ O2⟶

bullO2minus

(7)

bullO2minus

+ 2H+⟶ H2O2 + O2 (8)

H2O2⟶ HObull+

bullOH (9)



(10)



(11)







removal Remark Ref



H2SO4



[13]

Ag-ZnORGO


AgNO3 ethanol




[15]

Graphene-AgZnO




[8]







isstudy



4 Conclusion


Data Availability




Acknowledgments


References
























































Journal of

Chemistry





Journal of

Volume 2018






Volume 2018




Journal of






Enzyme Research


Journal of



MaterialsJournal of






Na

nom

ate

ria

ls







(a)


(b)

C Ka1

(c)

O Ka1

(d)

Zn Ka1

(e)

Ag La1

(f )



Zn2pZn 2p32

Zn 2p12

1015 1020 1025 1030 1035 1040 1045 1050

Inte

nsity

(au

)

Binding energy (eV)

ZnOAg-ZnOGO

(a)

C1sC-CC=C

C-OC=O

Zn-C

280 285 290 295

Inte

nsity

(au

)

Binding energy (eV)

ZnOAg-ZnOGO

(b)

O1s

525 530 535 540 545

Inte

nsity

(au

)

Binding energy (eV)

ZnOAg-ZnOGO

(c)

360 365 370 375 380

Inte

nsity

(au

)

Binding energy (eV)

Ag3dAg3d52

Ag3d32

Ag-ZnOGO

(d)

Ag-ZnOGO

Zn2p

O1s

Ag3dC1s

Inte

nsity

(au

)


(e)







200 300 400 500 600 700 800Wavelength (nm)

Diff

use r

efle

ctan

ce (

)

292eV

(αhυ

)2 (eV

cm

)2

315eV


ZnOAg-ZnOGO

(a)

Wavelength (nm)

Abso

rban

ce (a

u)

Ag-ZnOGO

ZnO

06

05

04

03

02

200 300 400 500 600 700

(b)


120

100

80

60

40

20

0


Qua

ntity

adso

rbed

(cm

3 g S

TP)

00 02 04 06 08 10

ZnOAg-ZnOGO


ZnO

Ag-ZnOGO

Wavelength (nm)

Inte

nsity

(au

)

350 400 450 500 550 600 650








12

10

08

06

04

02

00 Dark

CC 0

Light irradiation



(a)

Abso

rban

ce (a

u)

400 500 600 700 800Wavelength (nm)



(b)


CC 0

10

08

06

04

02

00

Time (min)0 30 60 90 120 150 180













+ eminus

( 1113857 (3)

CC 0

10

08

06

04

02




95

90

85

80

75

70

65

Deg

rada

tion

effic

ienc

y (

)

pH

35ndash

4

45ndash

5

55ndash

6

65ndash

7

75ndash

8

85ndash

9

95ndash

10

105

ndash11

115

ndash12

(a)


Deg

rada

tion

effic

ienc

y (

)

90

85

80

75

70

04

06

08

10

12

14

16

18

20

(b)

0 5 10 15 20 25

75

80

85

90


Deg

rada

tion

effic

ienc

y (

)

(c)


Energy (eV)

GO

MB

MBlowast

O2

ndash045eV

h+ h+ h+ h+ h+ h+


ZnOBand gap= 33eV

Vacuum level

CB (ndash42eV)

VB (ndash75eV)

endash

endash

endash

endash


AgAg2Ag3

Agn


Narrowed band gap

ndash442eV

(a)

(b)

(c)





h++ H2O⟶ H+

+ OHbull(4)

2h++ 2H2O⟶ 2H+

+ H2O2 (5)

H2O2⟶ HObull+

bullOH (6)


2eminus+ O2⟶

bullO2minus

(7)

bullO2minus

+ 2H+⟶ H2O2 + O2 (8)

H2O2⟶ HObull+

bullOH (9)



(10)



(11)







removal Remark Ref



H2SO4



[13]

Ag-ZnORGO


AgNO3 ethanol




[15]

Graphene-AgZnO




[8]







isstudy



4 Conclusion


Data Availability




Acknowledgments


References
























































Journal of

Chemistry





Journal of

Volume 2018






Volume 2018




Journal of






Enzyme Research


Journal of



MaterialsJournal of






Na

nom

ate

ria

ls




Zn2pZn 2p32

Zn 2p12

1015 1020 1025 1030 1035 1040 1045 1050

Inte

nsity

(au

)

Binding energy (eV)

ZnOAg-ZnOGO

(a)

C1sC-CC=C

C-OC=O

Zn-C

280 285 290 295

Inte

nsity

(au

)

Binding energy (eV)

ZnOAg-ZnOGO

(b)

O1s

525 530 535 540 545

Inte

nsity

(au

)

Binding energy (eV)

ZnOAg-ZnOGO

(c)

360 365 370 375 380

Inte

nsity

(au

)

Binding energy (eV)

Ag3dAg3d52

Ag3d32

Ag-ZnOGO

(d)

Ag-ZnOGO

Zn2p

O1s

Ag3dC1s

Inte

nsity

(au

)


(e)







200 300 400 500 600 700 800Wavelength (nm)

Diff

use r

efle

ctan

ce (

)

292eV

(αhυ

)2 (eV

cm

)2

315eV


ZnOAg-ZnOGO

(a)

Wavelength (nm)

Abso

rban

ce (a

u)

Ag-ZnOGO

ZnO

06

05

04

03

02

200 300 400 500 600 700

(b)


120

100

80

60

40

20

0


Qua

ntity

adso

rbed

(cm

3 g S

TP)

00 02 04 06 08 10

ZnOAg-ZnOGO


ZnO

Ag-ZnOGO

Wavelength (nm)

Inte

nsity

(au

)

350 400 450 500 550 600 650








12

10

08

06

04

02

00 Dark

CC 0

Light irradiation



(a)

Abso

rban

ce (a

u)

400 500 600 700 800Wavelength (nm)



(b)


CC 0

10

08

06

04

02

00

Time (min)0 30 60 90 120 150 180













+ eminus

( 1113857 (3)

CC 0

10

08

06

04

02




95

90

85

80

75

70

65

Deg

rada

tion

effic

ienc

y (

)

pH

35ndash

4

45ndash

5

55ndash

6

65ndash

7

75ndash

8

85ndash

9

95ndash

10

105

ndash11

115

ndash12

(a)


Deg

rada

tion

effic

ienc

y (

)

90

85

80

75

70

04

06

08

10

12

14

16

18

20

(b)

0 5 10 15 20 25

75

80

85

90


Deg

rada

tion

effic

ienc

y (

)

(c)


Energy (eV)

GO

MB

MBlowast

O2

ndash045eV

h+ h+ h+ h+ h+ h+


ZnOBand gap= 33eV

Vacuum level

CB (ndash42eV)

VB (ndash75eV)

endash

endash

endash

endash


AgAg2Ag3

Agn


Narrowed band gap

ndash442eV

(a)

(b)

(c)





h++ H2O⟶ H+

+ OHbull(4)

2h++ 2H2O⟶ 2H+

+ H2O2 (5)

H2O2⟶ HObull+

bullOH (6)


2eminus+ O2⟶

bullO2minus

(7)

bullO2minus

+ 2H+⟶ H2O2 + O2 (8)

H2O2⟶ HObull+

bullOH (9)



(10)



(11)







removal Remark Ref



H2SO4



[13]

Ag-ZnORGO


AgNO3 ethanol




[15]

Graphene-AgZnO




[8]







isstudy



4 Conclusion


Data Availability




Acknowledgments


References
























































Journal of

Chemistry





Journal of

Volume 2018






Volume 2018




Journal of






Enzyme Research


Journal of



MaterialsJournal of






Na

nom

ate

ria

ls








200 300 400 500 600 700 800Wavelength (nm)

Diff

use r

efle

ctan

ce (

)

292eV

(αhυ

)2 (eV

cm

)2

315eV


ZnOAg-ZnOGO

(a)

Wavelength (nm)

Abso

rban

ce (a

u)

Ag-ZnOGO

ZnO

06

05

04

03

02

200 300 400 500 600 700

(b)


120

100

80

60

40

20

0


Qua

ntity

adso

rbed

(cm

3 g S

TP)

00 02 04 06 08 10

ZnOAg-ZnOGO


ZnO

Ag-ZnOGO

Wavelength (nm)

Inte

nsity

(au

)

350 400 450 500 550 600 650








12

10

08

06

04

02

00 Dark

CC 0

Light irradiation



(a)

Abso

rban

ce (a

u)

400 500 600 700 800Wavelength (nm)



(b)


CC 0

10

08

06

04

02

00

Time (min)0 30 60 90 120 150 180













+ eminus

( 1113857 (3)

CC 0

10

08

06

04

02




95

90

85

80

75

70

65

Deg

rada

tion

effic

ienc

y (

)

pH

35ndash

4

45ndash

5

55ndash

6

65ndash

7

75ndash

8

85ndash

9

95ndash

10

105

ndash11

115

ndash12

(a)


Deg

rada

tion

effic

ienc

y (

)

90

85

80

75

70

04

06

08

10

12

14

16

18

20

(b)

0 5 10 15 20 25

75

80

85

90


Deg

rada

tion

effic

ienc

y (

)

(c)


Energy (eV)

GO

MB

MBlowast

O2

ndash045eV

h+ h+ h+ h+ h+ h+


ZnOBand gap= 33eV

Vacuum level

CB (ndash42eV)

VB (ndash75eV)

endash

endash

endash

endash


AgAg2Ag3

Agn


Narrowed band gap

ndash442eV

(a)

(b)

(c)





h++ H2O⟶ H+

+ OHbull(4)

2h++ 2H2O⟶ 2H+

+ H2O2 (5)

H2O2⟶ HObull+

bullOH (6)


2eminus+ O2⟶

bullO2minus

(7)

bullO2minus

+ 2H+⟶ H2O2 + O2 (8)

H2O2⟶ HObull+

bullOH (9)



(10)



(11)







removal Remark Ref



H2SO4



[13]

Ag-ZnORGO


AgNO3 ethanol




[15]

Graphene-AgZnO




[8]







isstudy



4 Conclusion


Data Availability




Acknowledgments


References
























































Journal of

Chemistry





Journal of

Volume 2018






Volume 2018




Journal of






Enzyme Research


Journal of



MaterialsJournal of






Na

nom

ate

ria

ls









12

10

08

06

04

02

00 Dark

CC 0

Light irradiation



(a)

Abso

rban

ce (a

u)

400 500 600 700 800Wavelength (nm)



(b)


CC 0

10

08

06

04

02

00

Time (min)0 30 60 90 120 150 180













+ eminus

( 1113857 (3)

CC 0

10

08

06

04

02




95

90

85

80

75

70

65

Deg

rada

tion

effic

ienc

y (

)

pH

35ndash

4

45ndash

5

55ndash

6

65ndash

7

75ndash

8

85ndash

9

95ndash

10

105

ndash11

115

ndash12

(a)


Deg

rada

tion

effic

ienc

y (

)

90

85

80

75

70

04

06

08

10

12

14

16

18

20

(b)

0 5 10 15 20 25

75

80

85

90


Deg

rada

tion

effic

ienc

y (

)

(c)


Energy (eV)

GO

MB

MBlowast

O2

ndash045eV

h+ h+ h+ h+ h+ h+


ZnOBand gap= 33eV

Vacuum level

CB (ndash42eV)

VB (ndash75eV)

endash

endash

endash

endash


AgAg2Ag3

Agn


Narrowed band gap

ndash442eV

(a)

(b)

(c)





h++ H2O⟶ H+

+ OHbull(4)

2h++ 2H2O⟶ 2H+

+ H2O2 (5)

H2O2⟶ HObull+

bullOH (6)


2eminus+ O2⟶

bullO2minus

(7)

bullO2minus

+ 2H+⟶ H2O2 + O2 (8)

H2O2⟶ HObull+

bullOH (9)



(10)



(11)







removal Remark Ref



H2SO4



[13]

Ag-ZnORGO


AgNO3 ethanol




[15]

Graphene-AgZnO




[8]







isstudy



4 Conclusion


Data Availability




Acknowledgments


References
























































Journal of

Chemistry





Journal of

Volume 2018






Volume 2018




Journal of






Enzyme Research


Journal of



MaterialsJournal of






Na

nom

ate

ria

ls












+ eminus

( 1113857 (3)

CC 0

10

08

06

04

02




95

90

85

80

75

70

65

Deg

rada

tion

effic

ienc

y (

)

pH

35ndash

4

45ndash

5

55ndash

6

65ndash

7

75ndash

8

85ndash

9

95ndash

10

105

ndash11

115

ndash12

(a)


Deg

rada

tion

effic

ienc

y (

)

90

85

80

75

70

04

06

08

10

12

14

16

18

20

(b)

0 5 10 15 20 25

75

80

85

90


Deg

rada

tion

effic

ienc

y (

)

(c)


Energy (eV)

GO

MB

MBlowast

O2

ndash045eV

h+ h+ h+ h+ h+ h+


ZnOBand gap= 33eV

Vacuum level

CB (ndash42eV)

VB (ndash75eV)

endash

endash

endash

endash


AgAg2Ag3

Agn


Narrowed band gap

ndash442eV

(a)

(b)

(c)





h++ H2O⟶ H+

+ OHbull(4)

2h++ 2H2O⟶ 2H+

+ H2O2 (5)

H2O2⟶ HObull+

bullOH (6)


2eminus+ O2⟶

bullO2minus

(7)

bullO2minus

+ 2H+⟶ H2O2 + O2 (8)

H2O2⟶ HObull+

bullOH (9)



(10)



(11)







removal Remark Ref



H2SO4



[13]

Ag-ZnORGO


AgNO3 ethanol




[15]

Graphene-AgZnO




[8]







isstudy



4 Conclusion


Data Availability




Acknowledgments


References
























































Journal of

Chemistry





Journal of

Volume 2018






Volume 2018




Journal of






Enzyme Research


Journal of



MaterialsJournal of






Na

nom

ate

ria

ls




95

90

85

80

75

70

65

Deg

rada

tion

effic

ienc

y (

)

pH

35ndash

4

45ndash

5

55ndash

6

65ndash

7

75ndash

8

85ndash

9

95ndash

10

105

ndash11

115

ndash12

(a)


Deg

rada

tion

effic

ienc

y (

)

90

85

80

75

70

04

06

08

10

12

14

16

18

20

(b)

0 5 10 15 20 25

75

80

85

90


Deg

rada

tion

effic

ienc

y (

)

(c)


Energy (eV)

GO

MB

MBlowast

O2

ndash045eV

h+ h+ h+ h+ h+ h+


ZnOBand gap= 33eV

Vacuum level

CB (ndash42eV)

VB (ndash75eV)

endash

endash

endash

endash


AgAg2Ag3

Agn


Narrowed band gap

ndash442eV

(a)

(b)

(c)





h++ H2O⟶ H+

+ OHbull(4)

2h++ 2H2O⟶ 2H+

+ H2O2 (5)

H2O2⟶ HObull+

bullOH (6)


2eminus+ O2⟶

bullO2minus

(7)

bullO2minus

+ 2H+⟶ H2O2 + O2 (8)

H2O2⟶ HObull+

bullOH (9)



(10)



(11)







removal Remark Ref



H2SO4



[13]

Ag-ZnORGO


AgNO3 ethanol




[15]

Graphene-AgZnO




[8]







isstudy



4 Conclusion


Data Availability




Acknowledgments


References
























































Journal of

Chemistry





Journal of

Volume 2018






Volume 2018




Journal of






Enzyme Research


Journal of



MaterialsJournal of






Na

nom

ate

ria

ls





h++ H2O⟶ H+

+ OHbull(4)

2h++ 2H2O⟶ 2H+

+ H2O2 (5)

H2O2⟶ HObull+

bullOH (6)


2eminus+ O2⟶

bullO2minus

(7)

bullO2minus

+ 2H+⟶ H2O2 + O2 (8)

H2O2⟶ HObull+

bullOH (9)



(10)



(11)







removal Remark Ref



H2SO4



[13]

Ag-ZnORGO


AgNO3 ethanol




[15]

Graphene-AgZnO




[8]







isstudy



4 Conclusion


Data Availability




Acknowledgments


References
























































Journal of

Chemistry





Journal of

Volume 2018






Volume 2018




Journal of






Enzyme Research


Journal of



MaterialsJournal of






Na

nom

ate

ria

ls





4 Conclusion


Data Availability




Acknowledgments


References
























































Journal of

Chemistry





Journal of

Volume 2018






Volume 2018




Journal of






Enzyme Research


Journal of



MaterialsJournal of






Na

nom

ate

ria

ls






































Journal of

Chemistry





Journal of

Volume 2018






Volume 2018




Journal of






Enzyme Research


Journal of



MaterialsJournal of






Na

nom

ate

ria

ls









Journal of

Chemistry





Journal of

Volume 2018






Volume 2018




Journal of






Enzyme Research


Journal of



MaterialsJournal of






Na

nom

ate

ria

ls




Date post:	27-May-2020
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SynergisticAdsorptionandPhotocatalyticActivityunderVisible IrradiationUsingAg-ZnO...

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