hydrothermal synthesis of pbo /rgo nanocomposite for...

Research ArticleHydrothermal Synthesis of PbO2RGO Nanocomposite forElectrocatalytic Degradation of Cationic Red X-GRL

Weidong Li12 Huayun Yang2 and Qi Liu3

1Qianjiang College Hangzhou Normal University Hangzhou 310036 China2Environmental College Zhejiang University of Technology Hangzhou 310032 China3College of Life and Environmental Sciences Hangzhou Normal University Hangzhou China

Correspondence should be addressed to Weidong Li lwdhznueducn

Received 4 December 2016 Accepted 26 January 2017 Published 13 March 2017

Academic Editor Philip D Rack

Copyright copy 2017 Weidong Li et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

PbO2 nanoparticles were prepared using a simple hydrothermal method with 120573-PbO as precursor and ammonium peroxydisulfateas oxidant During the hydrothermal condition with ammonium peroxydisulfate the formed hydroxyl radical has played a keyrole in the oxidation of 120573-PbO to PbO2 The size of as-prepared PbO2 nanoparticles was in the range of 25ndash50 nm Reducedgraphene oxide (RGO) was successfully prepared by the simple reduction reaction of graphene oxide by sodium borohydrideand the obtained RGO was then incorporated into the PbO2 nanoparticles The surface of ITO electrode was modified with theas-prepared PbO2RGO nanocomposite The constructed PbO2RGOITO electrode was subsequently applied for the catalyticdegradation of cationic red X-GRL which was an azo dye in wastewater The effects of reaction time applied current density andinitial concentration of dye on the color removal and COD removal were thoroughly investigated All results demonstrated that thedegradation performance of the electrode modified with PbO2RGO nanocomposite was extremely excellent

1 Introduction

A large amount ofwastewater has been produced in the textileindustry since the consumption of chemical dyes andwater inthe dye bleeding processes in high demand Owing to plentyof organic matters in wastewater (ie high chemical oxygendemand (COD)) and the hard degradation the effluentsare difficult to deal with using conventional treatmentsleading to the emerge of severe environmental problems [1]Cathonic red X-GRL a kind of azo dye is widely appliedin various industries including varnish plastic and textileUnfortunately X-GRL is hard to be degraded by conventionalprocess [2] With the increasing concern of environmentalprotection and more and more strict legislation the wastew-ater produced from textile industry must be purified beforethe discharge Recently several techniques including wet airoxidation (WAO) [3ndash5] catalytic wet air oxidation (CWAO)[6] and electrochemical oxidation [7] have been employed forthe treatment of the wastewater Owing to the unaffordablecost resulted from the demand of long operation time withhigh oxygen pressure and temperature the wide application

of traditional WAO is extremely limited As to CWAO theharsh operating conditions can be alleviated [8] and certainproblems such as the efficiency reduction and secondarypollution still exist

In recent years advanced electrochemical oxidation pro-cesses (AOPs) have received wide attention as an effectivetechnique for the treatment of wastewater composed ofundegradable and poisonous compounds AOPs possessgreat many advantages such as high efficiency environmentalcompatibility and most importantly easy applicability toautomation [9ndash11] As to AOPs the electrode materials arethe most important part which decide the efficiency andeconomy [12] Generally considering the degradation per-formance for organic pollutants the nonactive electrodesoutperform the active ones [13] For the degradation of azodye using electrochemical oxidation the performances ofvarious anodes including active carbon fiber (ACF) [14]Pt [15] PbO2 [16] SnO2 [17] RuO2 [18] and diamondelectrode [19 20] were investigated in detail Neverthelessowing to the low current efficiency possibly resulted fromlimited electrode surface area the dye removal performances

HindawiJournal of NanomaterialsVolume 2017 Article ID 1798706 7 pageshttpsdoiorg10115520171798706

2 Journal of Nanomaterials

obtained on these electrodes are not satisfactory Thereforethe exploration of new novel electrodes with high perfor-mance for the degradation of wastewater is highly required

For increasing the active surface area of the electrodereducing the particle size of the electrode material is avery effective method since much higher specific surfacearea can be achieved with nanosized materials Howevernanoparticles are easy to agglomerate which will result inelectrochemical performance degradation For the sake ofretaining the high specific surface area varieties of conduc-tive materials including conductive carbon materials andpolymers and metal oxides can be adopted as a substrate forthe electrode composed of nanomaterial Graphene a two-dimensional material with only one-atom-thick layer ofcarbon has attracted worldwide attentions owing to variousextraordinary properties such as ultrahigh surface area andunique conductivityTherefore graphene can be employed inelectrode materials for enhancing the electrocatalytic activity[21ndash23]

In this study the composite composed of nanosizedPbO2 and graphene was firstly prepared to the best of ourknowledgeThe as-prepared nanocompositewas then appliedin the modification of commercial electrode The perfor-mance of the PbO2-graphene nanocomposite for the azo dyedegradation was investigated Cationic red X-GRL a hardlybiodegradable dye that was widely used in various industriessuch as plastic textile and varnish has been employed as amodel organic substance in wastewater

2 Experimental

21 Chemicals and Materials Ammonium peroxydisulfategraphite powder (9999) with the particle size of 45120583mand orthogonal phase 120573-PbO were all obtained from Sigma-Aldrich and used as received Industrial cationic red X-GRL supplied by Jin-Jiang Chemical Dyestuff Co Ltd wasextractedwithmethanol at 50∘C in order to achieve a purity of995The obtained X-GRL with high purity was used as themodel pollutant Doubly distilled water was used in the entireexperiments

22 Preparation Graphene Oxide A modified Hummersrsquomethod was employed for the preparation of graphite oxidepowder from natural graphite powder [24] The graphiteoxide suspension with a yellow-brownish color was obtainedby dispersing the as-prepared graphite oxide powder intodoubly distilled water Then the obtained graphite oxidesuspension was sonicated under power of 150W and fre-quency of 40 kHz for 15min to promote the exfoliation ofgraphite oxide into graphene oxide sheets Finally unexfoli-ated graphite oxide was removed by treating the suspensionwith centrifugation at 6000 rpm for 30min

23 Hydrothermal Synthesis of Nanosized PbO2 1 g 120573-PbOwas mixed to 200mL distilled water and the mixture wassonicated for 30min in order to obtain a homogeneoussolution Subsequently 120mL ammonium peroxydisulfatesolution (05M) was mixed with the solution of 120573-PbO and

the mixture was treated with ultrasound for 1 h Then themixture was transferred to a Teflon lined autoclaves (500mL)and heated at 120∘C for 2 h After the reaction solution wascooled down a dark brown powder was obtained throughcentrifugation at 7500 rpm for 15min Finally the obtainedprecipitate was washed with water several times and dried inan oven at 70∘C for 1 h

24 Preparation of PbO2RGO Nanocomposite GO (50mg)was firstly dispersed into water (50mL) with sonicationfor 1 h Then nanosized PbO2 (05 g) was added to theGO suspension with sonication for another 1 h After theformation of a homogenous dispersion 10mL of NaBH4solution (1M) was quickly added to the solution and thenheated at 80∘C for 2 h under stirring After cooling downPbO2RGO was collected by treating the reaction solutionwith centrifugation at 7500 rpm for 15min

25 Electrode Modification ITO wafers were washed inacetone ethanol and DI water separately for 20min withsonicating and rinsed with plenty of doubly distilled waterand then dried under the atmosphere of N2 Subsequently1mL of PbO2RGO dispersion (1mgmL) was casted on theITO surface and dried at room temperature and the modifiedelectrode was denoted as PbO2RGOITO

26 Characterizations Powder X-ray Diffraction (PXRD)patterns of as-prepared samples were measured on Philipspowder diffractometer PW 304060 instrument with CuK120572 radiation (120582 = 1541 A) Morphological feature of thesamples was obtained on a field emission scanning electronmicroscope (SEM Hitachi-S4800) And the concentration ofred X-GRL was measured by a UV-vis spectrophotometer(Techcomp 8500 China) at wavelength of 530 nm

27 Electrocatalytic Degradation of Cationic Red X-GRLThe electrocatalytic degradation of cationic red X-GRL wasperformed in a cylindrical stainless autoclave (500mL) withstainless steel net as the cathode The experiments startedwhile the temperature of wastewater solution (250mL)within the reactor reached the set value During the entirecourse of the experiment the wastewater was stirred withsuitable stirring speed in order to guarantee the kineticallycontrolled reactions And the current density was kept con-stant at the selected value and the applied voltage was slightlyadjusted Dye concentration was analyzed spectrophotomet-rically by measuring the absorbance of the remaining dye atmaximum wavelength 530 nm on a UV-vis spectrophotome-ter The COD was measured by the standard method (closedrefluxphotometry) [25]

3 Results and Discussion

The lead oxide was converted to lead dioxide by the oxidationreaction using a strong oxidizing agent ammonium peroxy-disulfate The surface of PbO particles was firstly oxidized toPbO2 that was easily desorbed and the oxidation reactionrepeated on the reexposed PbO surface [26] The color of

Journal of Nanomaterials 3

(221

)

(113

)

(202

)(2

20)(112

)

(102

) (121

)

(002

)

(111

)

(110

)

1210 16 188 14 2062 Theta

0

250

500

750

1000

Inte

nsity

Figure 1 XRD pattern of synthesized PbO2 synthesized under120∘C

solution changed from original yellow to dark brown afterthe hydrothermal reactionThe reactive radicals were formedduring the oxidation reaction and the specific mechanismsteps are as follows

(NH4)2 S2O8 + 2H2O 997888rarr 2HSO4∙ + 2NH4OH

HSO4∙ +H2O 997888rarr H2SO4 +OH

∙

PbO +OH∙Hydrothermal997888997888997888997888997888997888997888997888997888997888rarr PbO (OH)

PbO (OH) +OH∙Hydrothermal997888997888997888997888997888997888997888997888997888997888rarr PbO (OH)2

PbO (OH)2 lArrrArr PbO2 +H2O

(1)

As can be seen from the XRD pattern of the as-preparedsample (Figure 1) the characteristic peaks of PbO2 appearedand almost no peak of PbOwas observedTherefore it can beconcluded that the conversion rate of PbO to PbO2 was closeto 100 The peaks at 723∘ 905∘ 1072∘ 1205∘ 1219∘ 1297∘1501∘ 1588∘ 1603∘ and 1775∘ are attributed to the (110) (111)(002) (102) (121) (112) (220) (202) and (221) planes of 120572-PbO2 The preparation of PbO2 using 120573-PbO as precursor ishighly effective

For the sake of investigating the influence of temperatureon the particle size of prepared PbO2 the hydrothermal reac-tionwas performed at 100∘C 120∘C 140∘C and 160∘C respec-tively On the basis of XRD spectra the complete transforma-tion of PbO can be achieved at 120∘C 140∘C and 160∘C aswell In contrast only partial of PbO was converted tothe PbO2 at 100

∘C possibly owing to the fact that the amountof formed OH∙ that owns the ability of converting PbO toPbO2 was extremely low [26]The SEM images of as-preparedPbO2 at 120∘C 140∘C and 160∘C were shown in Figures2(a)ndash2(c) respectively It can be obviously seen that the parti-cle size of PbO2 increased as the increasing temperature Theparticles were in the 20 to 50 nm size range when the reactionwas carried out at 120∘C while in the 75 to 150 nm size

range when the reaction was carried out at 160∘C Finally120∘C was chosen for all following experiments because thehigh demand of high specific surface area can be achievedby small particle size The SEM image of the as-preparednanocomposite of PbO2RGO was shown in Figure 2(d)PbO2 was embedded uniformly in RGO sheets indicating thesuccessful preparation of PbO2RGO nanocomposite

Figure 3 showed the absorption spectra of X-GRL aftercertain degradation on the PbO2RGOITO electrode For X-GRL a characteristic peak absorbance value at 530 nm in thevisible region was observed Besides another two absorbancepeaks at 240ndash250 nm and 280ndash290 nm in the ultravioletregion were also observed [27 28] The observed uniqueabsorbance peaks can be attributed to azo linkage (ndashN=Nndash)and benzene ring contained in X-GRL The absorbance peakof azo bond (ndashN=Nndash) that resulted from the 119899 rarr 120587lowasttransition mainly appeared in the visible region And theabsorbance peak of benzene ring that resulted from the120587 rarr 120587lowast transition mainly appeared in ultraviolet region(240ndash250 nm) As can be seen in Figure 3 with the occur-rence of degradation reaction the absorbency in the vis-ible region decreased quickly and the absorbency in theultraviolet region increased in contrast suggesting the breakof azo bond and the generation of many intermediate prod-ucts with benzene ring With the breakage of azo group theabsorbance at 240ndash250 nm also increased a little while theabsorbance at 280ndash290 nm was observed to decrease

The relationship between the removal of color and CODof red X-GRL and reaction time using the PbO2RGOITOelectrode was shown in Figure 4(a) The removal efficiencyof color (884) was higher than that of COD (375) sug-gesting more chromophore structure of X-GRL was brokenaccompanied by the production of some acidic intermediatesThe removal efficiencies of both color and COD showedan increase with increasing time and no obvious decreasetrend was observed suggesting the excellent stability of thePbO2RGOITO electrode The average current efficiency(ACE) and energy consumption (EC) were also investigatedand the calculation equations were as follows

ACE =(COD0 minus COD119905) 119865119881

8119868119905times 100

EC = 119880119868119905

36 (COD0 minus COD119905) 119881

(2)

where COD0 and CODt are the chemical oxygen demand atinitial time and given time 119905 (g O2L) respectively 119865 is theFaraday constant (96487Cmol) 119868 is the current (A) 119905 is thetreatment time (s)119881 is the volume of the solution (L) and 119880is the voltage applied (V)

As shown in Figure 4(b) the ACE decreased while theEC increased linearly with the COD removal which possiblywas ascribed to the complexity of the formed intermediatesAt the initial stage the ACE was very high with the value of991 and then decreased with the increasing COD removalWhen the COD removal efficiency was higher than 20the decrease of ACE became insignificant and the finalobtained ACE value was 537 after being treated for 240min The downward trend over time was similar to other


120∘C

100nm

(a)

140∘C

100nm

(b)

160∘C

100nm

(c)

50nm

(d)

Figure 2 SEM images of PbO2 synthesized under (a) 120∘C (b) 140∘C and (c) 160∘C (d) SEM image of the PbO2RGO nanocomposite

180

0min

700400 500 600300200Wavelength (nm)

00

01

02

03

04

05

06

07

Abso

rban

ce

Figure 3 UV-vis spectra for cationic red X-GRL degradation byPbO2RGOITO

reports [20 29] and the proposed explanation for the contin-uing decreasing ACE was the difficulty in the decompositionof generated organic acids The current efficiency for thedegradation of azo dye obtained in this study was higher thanthat reported in other works (less than 40) [18 30]indicating the excellent performance of the proposed novelanode for the electrochemical oxidation of cationic red X-GRL

Table 1 The effect of current density on color and COD removalACE and EC

Currentdensity(mAcm2)

Color () COD () ACE () EC (kWhkgCOD)

05 415 105 939 1011 616 194 598 2713 884 357 513 432

The effects of current density on color removal CODremoval ACE and EC were investigated and the resultswere shown in Table 1 Obviously the removal efficienciesof both color and COD were higher when higher currentdensity applied whichwas possibly ascribed to the increasingproduction rate of hydroxyl radical that decided the dyedegradationwith increasing current densityThe removal effi-ciency of color (COD)was 433 (130) and 871 (382) atthe applied current density of 08mAcm2 and 48mAcm2respectively indicating that current density is a very impor-tant parameter that affects the removal efficiency greatlyNevertheless the ACE showed a decrease with the increasingcurrent density demonstrating that the degradation wasless efficient as the current density increased When thedegradation process took place for 120min theACEobtainedwas 939 and 513 at the current density of 05mAcm2and 3mAcm2 respectively The decrease of degradationefficiency was probably caused by the occurrence of side


CODColor

50 100 150 200 2500

Time (min)

0

20

40

60

80

100

Deg

rada

tion

rate

()

(a)

20

30

40

50

60

70

ACE

()

5 10 15 20 25 30 35 400

Removal rate ()

12

16

20

24

28

32

36

40

EC (k

Wh

kgCO

D)

(b)

Figure 4 (a) Effect of degradation time on color removal and COD removal using PbO2RGOITO (b) Variation of ACE and EC with CODremoval (pH 50 cationic red X-GRL 500 mgL current density 10mAcm2 Na2SO4 3 gL 119879 25

∘C)

2000mgL1000mgL

500mgL300mgL

20 40 60 80 100 1200Time (min)

0

10

20

30

40

50

60

70

Rem

oval

rate

()

Figure 5 Effect of initial dye concentration on color and CODremoval (pH 50 Na2SO4 3 gL current density 10mAcm2 11987925∘C)

reactions such as oxygen evolution at certain currents Inaddition the EC increased from 101 to 432 kWhkg CODGenerally long treatment time but less cost was requiredfor the degradation process when low current density wasused In contrast high current density employed will lead toshort treatment time but costlyTherefore for comprehensiveconsideration of current efficiency and removal efficiency thecurrent density of 10mAcm2 would be the best choice atwhich condition of the color removal COD removal andACE would be relatively high and EC was acceptable

The influence of initial concentration of X-GRL on theremoval efficiency of color was also investigated and theresults were shown in Figure 5 The removal efficiency of

color was 693 within 120min at the initial concentration of300mgL However the removal efficiency of color decreasedto 167 as the initial concentration increased to 2000mgLThe decrease of color removal possibly resulted from thedecreasing ratio of formed hydroxyl radical to dye concen-tration In addition the absolute removal amount increaseddespite the decreased removal efficiency of color alongwith increasing initial concentration The absolute removalamount of X-GRL increased from 2091 to 3617mgL asthe initial concentration increased from 300 to 2000mgLMoreover the ACE (EC) obtained at the initial concentrationof 300 mgL and 2000 mgL were about 632 (294 kWhkgCOD) and 889 (185 kWhkg COD) respectively Thoughlower COD removal was observed with higher initial con-centration the COD removal can be enhanced with muchmore time Besides the ACE and EC changed little when theinitial concentration varied in the range of 500ndash2000mgLAs a result the proposed technique in this study was alsosuitable for the degradation of dye wastewater with highconcentration

4 Conclusions

In our work a simple hydrothermal method was employedfor the preparation of PbO2 nanoparticles with 120573-PbO asprecursor and ammonium peroxydisulfate as oxidant Thesize of as-prepared PbO2 nanoparticles was in the range of20ndash50 nm The PbO2RGO nanocomposite was successfullyprepared by incorporating RGO with PbO2 The fabricatedPbO2RGOITO electrode can be applied for the electrocat-alytic degradation of redX-GRL contained inwastewaterThedegradation process is cost-effective but poorly effective withthe applied low current density while it is highly effective butcostly with the applied high current densityThe removal rateincreased with the increasing temperature and the decreasinginitial dye concentration as well


Conflicts of Interest

The authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

Thiswork is supported by theNational Natural Science Foun-dation of China (nos 21207030 and 21207028) and ScienceFoundation of Zhejiang Province China (nos LY15B070013)

References

[1] G Mishra and M Tripathy ldquoA critical review of the treatmentsfor decolourization of textile effluentrdquo Colourage vol 40 pp35ndash35 1993

[2] Q Dai M Zhou and L Lei ldquoWet electrolytic oxidation ofcationic red X-GRLrdquo Journal of Hazardous Materials vol 137no 3 pp 1870ndash1874 2006

[3] V S Mishra V V Mahajani and J B Joshi ldquoWet air oxidationrdquoIndustrial and Engineering Chemistry Research vol 34 no 1 pp2ndash48 1995

[4] L Lei X Hu G Chen J F Porter and P L Yue ldquoWet airoxidation of desizing wastewater from the textile industryrdquoIndustrial and Engineering Chemistry Research vol 39 no 8 pp2896ndash2901 2000

[5] S K Bhargava J Tardio J Prasad K Foger D B Akolekarand S C Grocott ldquoWet oxidation and catalytic wet oxidationrdquoIndustrial and Engineering Chemistry Research vol 45 no 4 pp1221ndash1258 2006

[6] A Eftaxias J Font A Fortuny A Fabregat and F StuberldquoCatalytic wet air oxidation of phenol over active carboncatalyst Global kinetic modelling using simulated annealingrdquoApplied Catalysis B Environmental vol 67 no 1-2 pp 12ndash232006

[7] F H Oliveira M E Osugi F M Paschoal D Profeti P Oliviand M V B Zanoni ldquoElectrochemical oxidation of an acid dyeby active chlorine generated using TiSn(1minus119909)Ir119909O2 electrodesrdquoJournal of Applied Electrochemistry vol 37 no 5 pp 583ndash5922007

[8] J A Zazo J A Casas A F Mohedano and J J RodrıguezldquoCatalytic wet peroxide oxidation of phenol with a Feactivecarbon catalystrdquoApplied Catalysis B Environmental vol 65 no3-4 pp 261ndash268 2006

[9] K Rajeshwar J G Ibanez and G M Swain ldquoElectrochemistryand the environmentrdquo Journal of Applied Electrochemistry vol24 no 11 pp 1077ndash1091 1994

[10] C Comninellis ldquoElectrocatalysis in the electrochemical con-versioncombustion of organic pollutants for waste water treat-mentrdquoElectrochimicaActa vol 39 no 11-12 pp 1857ndash1862 1994

[11] M Zhou Z Wu and DWang ldquoElectrocatalytic degradation ofphenol in acidic and saline wastewaterrdquo Journal of Environmen-tal Science and Health Part A ToxicHazardous Substances andEnvironmental Engineering vol 37 no 7 pp 1263ndash1275 2002

[12] R Kotz S Stucki and B Carcer ldquoElectrochemical waste watertreatment using high overvoltage anodes Part I physical andelectrochemical properties of SnO2 anodesrdquo Journal of AppliedElectrochemistry vol 21 no 1 pp 14ndash20 1991

[13] P Canizares F Martınez M Dıaz J Garcıa-Gomez and MA Rodrigo ldquoElectrochemical oxidation of aqueous phenolwastes using active and nonactive electrodesrdquo Journal of theElectrochemical Society vol 149 no 8 pp D118ndashD124 2002

[14] J Jia J Yang J Liao W Wang and Z Wang ldquoTreatment ofdyeing wastewater with ACF electrodesrdquo Water Research vol33 no 3 pp 881ndash884 1999

[15] M A Sanroman M Pazos M T Ricart and C CameselleldquoElectrochemical decolourisation of structurally different dyesrdquoChemosphere vol 57 no 3 pp 233ndash239 2004

[16] H S Awad and N A Galwa ldquoElectrochemical degradation ofAcid Blue and Basic Brown dyes on PbPbO2 electrode in thepresence of different conductive electrolyte and effect of variousoperating factorsrdquo Chemosphere vol 61 no 9 pp 1327ndash13352005

[17] N Mohan and N Balasubramanian ldquoIn situ electrocatalyticoxidation of acid violet 12 dye effluentrdquo Journal of HazardousMaterials vol 136 no 2 pp 239ndash243 2006

[18] N Mohan N Balasubramanian and V Subramanian ldquoElec-trochemical treatment of simulated textile effluentrdquo ChemicalEngineering and Technology vol 24 no 7 pp 749ndash753 2001

[19] X Chen G Chen and P L Yue ldquoAnodic oxidation of dyes atnovel TiB-diamond electrodesrdquo Chemical Engineering Sciencevol 58 no 3ndash6 pp 995ndash1001 2003

[20] A Fernandes A Morao M Magrinho A Lopes and IGoncalves ldquoElectrochemical degradation of C I Acid Orange7rdquo Dyes and Pigments vol 61 no 3 pp 287ndash296 2004

[21] L Fu D Zhu and A Yu ldquoGalvanic replacement synthesisof silver dendrites-reduced graphene oxide composites andtheir surface-enhanced Raman scattering characteristicsrdquo Spec-trochimica Acta Part A Molecular and Biomolecular Spec-troscopy vol 149 pp 396ndash401 2015

[22] L Fu S Yu L Thompson and A Yu ldquoDevelopment of a novelnitrite electrochemical sensor by stepwise in situ formation ofpalladium and reduced graphene oxide nanocompositesrdquo RSCAdvances vol 5 no 50 pp 40111ndash40116 2015

[23] L Fu and A Yu ldquoElectroanalysis of dopamine using reducedgraphene oxide-palladium nanocompositesrdquo Nanoscience andNanotechnology Letters vol 7 no 2 pp 147ndash151 2015

[24] A Esfandiar O Akhavan and A Irajizad ldquoMelatonin as apowerful bio-antioxidant for reduction of graphene oxiderdquoJournal of Materials Chemistry vol 21 no 29 pp 10907ndash109142011

[25] APHA AWWA and WEF Standard Method for the Examina-tion of Water and Wastewater APHA Washington DC USA19th edition 1995

[26] S Ghasemi M F Mousavi M Shamsipur and H KaramildquoSonochemical-assisted synthesis of nano-structured lead diox-iderdquoUltrasonics Sonochemistry vol 15 no 4 pp 448ndash455 2008

[27] Z Ren J Guan H Gao J Tian Y Wen and R ZhengldquoCharacteristics of cationic Red X-GRL adsorption by rawdiatomite and diatomite concentraterdquoPhysicochemical Problemsof Mineral Processing vol 52 no 1 pp 44ndash55 2016

[28] B Qiu X Xu H Guo Y Dang X Cheng and D SunldquoAnaerobic transformation of Cationic Red X-GRL with lowlevels of carbon sourcerdquo International Biodeterioration andBiodegradation vol 95 pp 102ndash109 2014


[29] M Zhou Q Dai L Lei C Ma and D Wang ldquoLong lifemodified lead dioxide anode for organic wastewater treatmentelectrochemical characteristics and degradation mechanismrdquoEnvironmental Science amp Technology vol 39 no 1 pp 363ndash3702005

[30] P Canizares A Gadri J Lobato et al ldquoElectrochemical oxida-tion of azoic dyes with conductive-diamond anodesrdquo Industrialand Engineering Chemistry Research vol 45 no 10 pp 3468ndash3473 2006

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obtained on these electrodes are not satisfactory Thereforethe exploration of new novel electrodes with high perfor-mance for the degradation of wastewater is highly required

For increasing the active surface area of the electrodereducing the particle size of the electrode material is avery effective method since much higher specific surfacearea can be achieved with nanosized materials Howevernanoparticles are easy to agglomerate which will result inelectrochemical performance degradation For the sake ofretaining the high specific surface area varieties of conduc-tive materials including conductive carbon materials andpolymers and metal oxides can be adopted as a substrate forthe electrode composed of nanomaterial Graphene a two-dimensional material with only one-atom-thick layer ofcarbon has attracted worldwide attentions owing to variousextraordinary properties such as ultrahigh surface area andunique conductivityTherefore graphene can be employed inelectrode materials for enhancing the electrocatalytic activity[21ndash23]

In this study the composite composed of nanosizedPbO2 and graphene was firstly prepared to the best of ourknowledgeThe as-prepared nanocompositewas then appliedin the modification of commercial electrode The perfor-mance of the PbO2-graphene nanocomposite for the azo dyedegradation was investigated Cationic red X-GRL a hardlybiodegradable dye that was widely used in various industriessuch as plastic textile and varnish has been employed as amodel organic substance in wastewater

2 Experimental

21 Chemicals and Materials Ammonium peroxydisulfategraphite powder (9999) with the particle size of 45120583mand orthogonal phase 120573-PbO were all obtained from Sigma-Aldrich and used as received Industrial cationic red X-GRL supplied by Jin-Jiang Chemical Dyestuff Co Ltd wasextractedwithmethanol at 50∘C in order to achieve a purity of995The obtained X-GRL with high purity was used as themodel pollutant Doubly distilled water was used in the entireexperiments

22 Preparation Graphene Oxide A modified Hummersrsquomethod was employed for the preparation of graphite oxidepowder from natural graphite powder [24] The graphiteoxide suspension with a yellow-brownish color was obtainedby dispersing the as-prepared graphite oxide powder intodoubly distilled water Then the obtained graphite oxidesuspension was sonicated under power of 150W and fre-quency of 40 kHz for 15min to promote the exfoliation ofgraphite oxide into graphene oxide sheets Finally unexfoli-ated graphite oxide was removed by treating the suspensionwith centrifugation at 6000 rpm for 30min

23 Hydrothermal Synthesis of Nanosized PbO2 1 g 120573-PbOwas mixed to 200mL distilled water and the mixture wassonicated for 30min in order to obtain a homogeneoussolution Subsequently 120mL ammonium peroxydisulfatesolution (05M) was mixed with the solution of 120573-PbO and

the mixture was treated with ultrasound for 1 h Then themixture was transferred to a Teflon lined autoclaves (500mL)and heated at 120∘C for 2 h After the reaction solution wascooled down a dark brown powder was obtained throughcentrifugation at 7500 rpm for 15min Finally the obtainedprecipitate was washed with water several times and dried inan oven at 70∘C for 1 h

24 Preparation of PbO2RGO Nanocomposite GO (50mg)was firstly dispersed into water (50mL) with sonicationfor 1 h Then nanosized PbO2 (05 g) was added to theGO suspension with sonication for another 1 h After theformation of a homogenous dispersion 10mL of NaBH4solution (1M) was quickly added to the solution and thenheated at 80∘C for 2 h under stirring After cooling downPbO2RGO was collected by treating the reaction solutionwith centrifugation at 7500 rpm for 15min

25 Electrode Modification ITO wafers were washed inacetone ethanol and DI water separately for 20min withsonicating and rinsed with plenty of doubly distilled waterand then dried under the atmosphere of N2 Subsequently1mL of PbO2RGO dispersion (1mgmL) was casted on theITO surface and dried at room temperature and the modifiedelectrode was denoted as PbO2RGOITO

26 Characterizations Powder X-ray Diffraction (PXRD)patterns of as-prepared samples were measured on Philipspowder diffractometer PW 304060 instrument with CuK120572 radiation (120582 = 1541 A) Morphological feature of thesamples was obtained on a field emission scanning electronmicroscope (SEM Hitachi-S4800) And the concentration ofred X-GRL was measured by a UV-vis spectrophotometer(Techcomp 8500 China) at wavelength of 530 nm

27 Electrocatalytic Degradation of Cationic Red X-GRLThe electrocatalytic degradation of cationic red X-GRL wasperformed in a cylindrical stainless autoclave (500mL) withstainless steel net as the cathode The experiments startedwhile the temperature of wastewater solution (250mL)within the reactor reached the set value During the entirecourse of the experiment the wastewater was stirred withsuitable stirring speed in order to guarantee the kineticallycontrolled reactions And the current density was kept con-stant at the selected value and the applied voltage was slightlyadjusted Dye concentration was analyzed spectrophotomet-rically by measuring the absorbance of the remaining dye atmaximum wavelength 530 nm on a UV-vis spectrophotome-ter The COD was measured by the standard method (closedrefluxphotometry) [25]

3 Results and Discussion

The lead oxide was converted to lead dioxide by the oxidationreaction using a strong oxidizing agent ammonium peroxy-disulfate The surface of PbO particles was firstly oxidized toPbO2 that was easily desorbed and the oxidation reactionrepeated on the reexposed PbO surface [26] The color of


(221

)

(113

)

(202

)(2

20)(112

)

(102

) (121

)

(002

)

(111

)

(110

)

1210 16 188 14 2062 Theta

0

250

500

750

1000

Inte

nsity





∙




(1)







ACE =(COD0 minus COD119905) 119865119881

8119868119905times 100

EC = 119880119868119905

36 (COD0 minus COD119905) 119881

(2)




120∘C

100nm

(a)

140∘C

100nm

(b)

160∘C

100nm

(c)

50nm

(d)


180

0min

700400 500 600300200Wavelength (nm)

00

01

02

03

04

05

06

07

Abso

rban

ce






05 415 105 939 1011 616 194 598 2713 884 357 513 432



CODColor

50 100 150 200 2500

Time (min)

0

20

40

60

80

100

Deg

rada

tion

rate

()

(a)

20

30

40

50

60

70

ACE

()

5 10 15 20 25 30 35 400

Removal rate ()

12

16

20

24

28

32

36

40

EC (k

Wh

kgCO

D)

(b)


∘C)

2000mgL1000mgL

500mgL300mgL

20 40 60 80 100 1200Time (min)

0

10

20

30

40

50

60

70

Rem

oval

rate

()





4 Conclusions





Acknowledgments


References







































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




(221

)

(113

)

(202

)(2

20)(112

)

(102

) (121

)

(002

)

(111

)

(110

)

1210 16 188 14 2062 Theta

0

250

500

750

1000

Inte

nsity





∙




(1)







ACE =(COD0 minus COD119905) 119865119881

8119868119905times 100

EC = 119880119868119905

36 (COD0 minus COD119905) 119881

(2)




120∘C

100nm

(a)

140∘C

100nm

(b)

160∘C

100nm

(c)

50nm

(d)


180

0min

700400 500 600300200Wavelength (nm)

00

01

02

03

04

05

06

07

Abso

rban

ce






05 415 105 939 1011 616 194 598 2713 884 357 513 432



CODColor

50 100 150 200 2500

Time (min)

0

20

40

60

80

100

Deg

rada

tion

rate

()

(a)

20

30

40

50

60

70

ACE

()

5 10 15 20 25 30 35 400

Removal rate ()

12

16

20

24

28

32

36

40

EC (k

Wh

kgCO

D)

(b)


∘C)

2000mgL1000mgL

500mgL300mgL

20 40 60 80 100 1200Time (min)

0

10

20

30

40

50

60

70

Rem

oval

rate

()





4 Conclusions





Acknowledgments


References







































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




120∘C

100nm

(a)

140∘C

100nm

(b)

160∘C

100nm

(c)

50nm

(d)


180

0min

700400 500 600300200Wavelength (nm)

00

01

02

03

04

05

06

07

Abso

rban

ce






05 415 105 939 1011 616 194 598 2713 884 357 513 432



CODColor

50 100 150 200 2500

Time (min)

0

20

40

60

80

100

Deg

rada

tion

rate

()

(a)

20

30

40

50

60

70

ACE

()

5 10 15 20 25 30 35 400

Removal rate ()

12

16

20

24

28

32

36

40

EC (k

Wh

kgCO

D)

(b)


∘C)

2000mgL1000mgL

500mgL300mgL

20 40 60 80 100 1200Time (min)

0

10

20

30

40

50

60

70

Rem

oval

rate

()





4 Conclusions





Acknowledgments


References







































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




CODColor

50 100 150 200 2500

Time (min)

0

20

40

60

80

100

Deg

rada

tion

rate

()

(a)

20

30

40

50

60

70

ACE

()

5 10 15 20 25 30 35 400

Removal rate ()

12

16

20

24

28

32

36

40

EC (k

Wh

kgCO

D)

(b)


∘C)

2000mgL1000mgL

500mgL300mgL

20 40 60 80 100 1200Time (min)

0

10

20

30

40

50

60

70

Rem

oval

rate

()





4 Conclusions





Acknowledgments


References







































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials






Acknowledgments


References







































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials













CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



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