Magnetite mesocellular carbon foam as a magnetically recoverable fenton catalyst

Magnetite/mesocellular carbon foam as a magnetically recoverable fenton catalyst for removal of phenol and arsenic

Jinyoung Chun a ,1,Hongshin Lee b ,1,Sang-Hyup Lee c ,Seok-Won Hong c ,Jaesang Lee c ,Changha Lee b ,?,Jinwoo Lee a ,?

a

Department of Chemical Engineering,Pohang University of Science and Technology (POSTECH),Pohang,Republic of Korea

b

School of Urban and Environmental Engineering,Ulsan National Institute of Science and Technology (UNIST),Ulsan,Republic of Korea c

Water Environmental Center,Korea Institute of Science and Technology (KIST),Seoul,Republic of Korea

h i g h l i g h t s

"We synthesize a magnetite-loaded mesocellular carbonaceous material,Fe 3O 4/MSU-F-C."Fe 3O 4/MSU-F-C exhibits superior activity as both a Fenton catalyst and an adsorbent."Fe 3O 4/MSU-F-C is easily separable from water by its strong magnetic property.

a r t i c l e i n f o Article history:

Received 20March 2012

Received in revised form 20July 2012Accepted 23July 2012

Available online 11August 2012Keywords:

Fenton reaction Water treatment

Mesoporous material Heterogeneous catalyst

a b s t r a c t

A magnetite-loaded mesocellular carbonaceous material,Fe 3O 4/MSU-F-C,exhibited superior activity as both a Fenton catalyst and an adsorbent for removal of phenol and arsenic,and strong magnetic property rendering it separable by simply applying magnetic ?eld.In the presence of hydrogen peroxide,the cat-alytic process by Fe 3O 4/MSU-F-C completely oxidized phenol and As(III)under the conditions where com-mercial iron oxides showed negligible effects.Notably,the decomposition of H 2O 2by Fe 3O 4/MSU-F-C was not faster than those by commercial iron oxides,indicating that hydroxyl radical produced via the cata-lytic process by Fe 3O 4/MSU-F-C was used more ef?ciently for the oxidation of target contaminants com-pared to the other iron oxides.The homogeneous Fenton reaction by the dissolved iron species eluted from Fe 3O 4/MSU-F-C was insigni?cant.At relatively high doses of Fe 3O 4/MSU-F-C,total concentration of arsenic decreased to a signi?cant extent due to the adsorption of arsenic on the catalyst surface.The removal of arsenic by adsorption was found to proceed via preoxidation of As(III)into As(V)and the subsequent adsorption of As(V)onto the catalyst.

ó2012Elsevier Ltd.All rights reserved.

1.Introduction

The effective removal of organic pollutants and toxic metals in wastewater is an important issue due to their hazard to human health and the environment.However,conventional chemical and biological methods for wastewater treatment are not ef?cient and their practical applications are limited (Gogate and Pandit,2004;Martinez et al.,2007;Jiang et al.,2009).To overcome this problem,advanced oxidation processes,one of powerful alterna-tive technology,have been developed and widely studied nowa-days (Hartmann et al.,2010).Strong oxidants such as the hydroxyl radical (?OH)generated from ozone,hydrogen peroxide (H 2O 2),oxygen,and air with speci?c catalyst have been mainly used in these processes (Yamamoto et al.,2009;Hartmann et al.,2010).Among the rest,Fenton process based on the reaction of fer-rous ion (Fe(II))with H 2O 2is well known to be very effective in the removal of various toxic materials (Neyens and Baeyens,2003;Li and Qu,2009).Considerable attention has been paid to Fenton reaction due to high ef?ciency,non-necessity of special equipment,low operation cost,and mild operating conditions (pressure and temperature)(Ramirez et al.,2007).

However,in spite of above-mentioned advantageous properties,homogeneous Fenton reaction has still some disadvantages for application such as recovery of iron ion to comply with environ-ment regulations and formation of unwanted iron sludge (Marti-nez et al.,2007;Ramirez et al.,2007).These drawbacks have been improved by introduction of heterogeneous Fenton catalysts using various support materials for immobilizing iron.Porous materials have been promising supports and adsorbents due to

0045-6535/$-see front matter ó2012Elsevier Ltd.All rights reserved.https://www.360docs.net/doc/b817158766.html,/10.1016/j.chemosphere.2012.07.046

?Corresponding authors.Tel.:+82522172812;fax.:+82522172019(C.Lee),tel.:+8222792395;fax:+8222795528(J.Lee).

E-mail addresses:clee@unist.ac.kr (C.Lee),jinwoo03@postech.ac.kr (J.Lee).1

These authors contributed equally to this work.

its large surface area and well-interconnected pores,however,zeo-litic materials and activated carbons having large fraction of micropores showed poor catalytic activity due to slow diffusion kinetics or pore blocking by large molecules(Clark and Macquarrie, 1996;Pattanayak et al.,2000;Gu et al.,2007;Yamamoto et al., 2009).Therefore,catalytic supports with relatively large pore sizes are required for practical applications.

Mesoporous materials are good candidates for satisfying this condition because of facile diffusion of reactants and products through the pores,regular and tunable pore size with uniform pore structure,and good physiochemical stability as well as their large surface area and pore volume(Martinez et al.,2005;Lim et al., 2006;Chen et al.,2009;Wu and Zhao,2011).Meanwhile,it is known that carbon based materials,which are thermally stable, chemically inert and low cost,show better adsorption property for organic pollutants compared with silica materials mainly owing to their hydrophobicity(Wu and Zhao,2011).Recently developed template methods allow the synthesis of various kinds of well-or-dered mesoporous carbon,with uniform pore sizes and large sur-face areas,which provide ef?cient morphology for their application as supports and adsorbent(Lee et al.,1999;Ryoo et al.,1999;Jun et al.,2000;Lee et al.,2001,2006).Accordingly, elimination of environmental pollutants such as degradation of dye(Ramirez et al.,2007),heavy metal adsorption(Gu and Deng, 2007;Gu et al.,2007),and the removal of organic phenolic com-pounds(Yamamoto et al.,2009;Zhang et al.,2011;Hu et al., 2012)using iron-loaded mesoporous carbon have been reported by several research groups.However,mesoporous carbons used in previous reports have some drawbacks for removal of pollu-tants.First of all,pore size is too small to load suf?cient amount of iron oxide nanoparticles on the inner pore walls since several nanometer sized particles of which particle size is similar to pore size are formed by impregnation method(Hu et al.,2012).Thus, large fraction of pores is blocked and the merits of porous structure cannot be used ef?ciently.Mesoporous carbon capsule partially solved the above mentioned problems,however,it required com-plex synthetic method and magnetic saturation value was rela-tively low(Zhang et al.,2011).In the case of loading of iron ions or small amount of iron oxide nanoparticles(Gu and Deng,2007; Gu et al.,2007;Ramirez et al.,2007;Yamamoto et al.,2009),cata-lyst contents are limited and suf?cient magnetic saturation value for magnetic separation cannot be provided.Therefore,decrease of catalytic activity and necessity of complex recovery steps are inevitable.

In this sense,development of mesoporous carbon with suitable pore structure is required and we employed a large pore-sized mesoporous carbon,mesocellular carbon foam(MSU-F-C),as a support material and adsorbent in this study.MSU-F-C,which has large interconnected pores(>25nm),with a large surface area ($1000m2gà1)and pore volume($1.5cm3gà1),provides several advantages over other types of mesoporous carbon with one-dimensional small-sized pores($3nm),such as CMK-3(Jun et al.,2000).Magnetite(Fe3O4)nanoparticles(>10nm)can be eas-ily incorporated onto the inner pore walls without blocking the pore entrance.Therefore,(i)a facile diffusion pathway through interconnected pores for catalytic reaction is assured even after loading of catalysts,(ii)ef?cient loading of large amount of nano-particles onto the carbon supports can be achieved using a simple impregnation method,(iii)high concentration of ferrous ion due to loading of large amount of magnetite(Fe3O4)allow the superior catalytic activity for Fenton reaction.Furthermore,well-dispersed large amount of small-sized($15nm)magnetite nanoparticles give magnetic functionality to catalytic adsorbent materials,which leads to facile magnetic separation after the removal of environ-mental https://www.360docs.net/doc/b817158766.html,pared with other iron oxides,magnetite is known to be the most effective heterogeneous Fenton catalyst due to the enhanced production of?OH by Fe(II)in its structure (Kong et al.,1998;Kwan and Voelker,2003;Gao et al.,2007;Zhang et al.,2008);thus it is employed as catalyst in this study.

Herein,we report the highly ef?cient removal of aqueous phe-nol and arsenic by the heterogeneous Fenton system,using Fe3O4 nanoparticles-loaded MSU-F-C(Fe3O4/MSU-F-C(Kang et al., 2011))as both a catalyst and an adsorbent.Fe3O4/MSU-F-C showed superior activity compared to commercial iron oxides,including magnetite(Fe3O4),hematite(a-Fe2O3)and goethite(a-FeOOH), and it was easily separated with a permanent magnet and re-dispersed into solution due to its favourable magnetic properties.

2.Materials and methods

2.1.Reagents

Iron(III)nitrate nonahydrate(98.5%,extra pure)and ethyl alco-hol(99.9%,guaranteed grade)were obtained from Samchun Chem-ical for synthesis of Fe3O4/MSU-F-C.All other chemicals were of reagent grade and were used as received without further puri?ca-tion.All aqueous solutions were prepared using18M O Milli-Q water from a Millipore system.10mM Stock solutions of iron (Fe(II))and arsenic(As(III),As(V))were prepared by dissolving fer-rous sulfate,sodium arsenite,and sodium arsenate in acidic solu-tion(10mM HCl).Stock solutions of phenol(10mM)and H2O2 (1M)was also prepared,respectively.The stock solutions were stored at4°C until use.Microsized powders of magnetite (Fe3O4),hematite(a-Fe2O3),goethite(a-FeOOH),and nanoparticu-late magnetite were obtained from Sigma–Aldrich Co.for compar-ative experiments with Fe3O4/MSU-F-C.The particle size and BET surface areas of commercial iron oxides are listed in the supple-mentary data(Table S1).

2.2.Synthesis of Fe3O4/MSU-F-C

MSU-F-C was prepared using mesocellular aluminosilicate foam as a silica template,following the previously reported procedures (Lee et al.,2001,2002).For the synthesis of Fe3O4(45wt.%)/ MSU-F-C,a wet impregnation method was employed(Kang et al., 2011).Brie?y,the desired amount of Fe(NO3)3á9H2O ethanolic solution was impregnated into the MSU-F-C at room temperature. After evaporation of the ethanol under stirring,the resultant mate-rials were heated to400°C for4h under a H2/Ar atmosphere.

2.3.Material characterization

The morphology was investigated using a scanning electron microscope(SEM,Hitachi S-4800)and a transmission electron microscope(TEM,Hitachi H-7600)operated at100kV.Energy-dis-persive X-ray spectroscopy(EDS)was performed on a JEOL JEM-2200FS instrument operated at200kV.The nitrogen adsorption/ desorption isotherms were measured at77K using a Tristar II 3020system(Micromeritics Instrument Corporation).The samples were degassed overnight at200°C before measurements.The sur-face areas of the samples were calculated from the isotherms according to the Brunauer–Emmett–Teller(BET)method and the pore volumes were taken at P/P o=0.995single point.Powder X-ray diffraction(XRD)patterns were obtained with a Rigaku D/max-2500diffractometer using CuK a radiation(k=1.5418?) at a scanning rate of 4.00°minà1.Thermogravimetic analysis (TGA)was performed using a Perkin Elmer TGS-2system under air atmosphere with a heating rate of10°C minà1.A magnetic property measurement was carried out using a superconducting quantum interference device(SQUID)magnetometer(Quantum Design,MPMS XL-7)at300K.

J.Chun et al./Chemosphere89(2012)1230–12371231

2.4.Apparatus and procedure for batch experiments of phenol and arsenic removal

The entire experiments for removal of phenol and arsenic were performed in batch systems with100mL Pyrex vials open to the atmosphere at room temperature(20±2°C).The solution pH was initially adjusted using0.1N HCl and0.1N NaOH,and the variation of pH was less than0.1units during the reaction.The experiments were initiated by adding an aliquot of H2O2stock solution to a pH-adjusted solution containing the target compound(phenol or As(III))and the iron oxide catalyst.Samples were withdrawn at pre-determined timed intervals,and?ltered immediately through a 0.45l m nylon?lter.All the experiments were carried out in tripli-cate,and average values and the standard deviations are presented.

2.5.Analytical methods

Phenol was analyzed using high-performance liquid chroma-tography(HPLC)with UV absorbance detection at270nm.Separa-tion was performed on a Dionex–Acclaim C18column using water with10mM nitric acid and acetonitrile as the eluent at a?ow rate of1.0mL minà1.The Fe(II)concentration in solution was measured using the1,10-phenanthroline method(Tamura et al.,1974).For the analysis of total iron concentration,Fe(III)was reduced to Fe(II) with hydroxylamine hydrochloride prior to the analysis of Fe(II). The analysis of As(V)was carried out using the molybdenum blue method(Dhar et al.,2004).The total arsenic concentration was determined by analyzing As(V)after As(III)was oxidized with potassium iodide solutions.The concentration of H2O2was quanti-?ed by the titanium sulfate method(Eisenberg,1943).

3.Results and discussion

3.1.Synthesis and characterization of Fe3O4/MSU-F-C

Large-pore sized mesoporous carbon,MSU-F-C,was synthe-sized by a hard template method using mesocellular aluminosili-cate foam and furfuryl alcohol as silica template and carbon precursor,respectively.Two kinds of pores existed in MSU-F-C: large cellular pores($30nm)originated from main pores of silica template and small sized pores($5nm)generated by the dissolu-tion of the walls of template(Lee et al.,2001,2002).The detailed structure of MSU-F-C and accompanied advantages for catalytic reaction will be discussed in next paragraph with material charac-terization.Fe3O4nanoparticles could be easily incorporated in MSU-F-C by simple wet impregnation method and subsequent heat treatment in H2/Ar atmosphere.Since part of Fe(III)ions in iron precursor can be reduced to Fe(II)ion by p-electrons present on the carbon surface as well as hydrogen gas(Montes-Moran et al.,2004;Ban et al.,2010),Fe3O4nanoparticles were successfully formed on the surface of MSU-F-C.

Fig.1a and b shows SEM and TEM image of MSU-F-C,respec-tively.As shown in these images,MSU-F-C was composed of sev-eral hundred nanometer-sized particles(Fig.1a)with well developed large-sized pores($30nm Fig.1b).This morphology facilitates the diffusion of organic waste materials into the pores as well as incorporation of catalyst nanoparticles.TEM image of Fe3O4/MSU-F-C(Fig.1c)and energy dispersive X-ray spectroscopy (EDS)elemental mapping analysis of C and Fe(See Fig.S1in the supplementary data)reveal that large amount of Fe3O4nanoparti-cles were?nely dispersed onto the inner pore surface of MSU-F-C without severe pore blockage.

The nitrogen adsorption/desorption isotherms(Fig.2a)and the pore size distribution of MSU-F-C obtained from the adsorption branch of the isotherms using the BJH(Barrett-Joyner-Halenda)method(Fig.2b)also indicates the existence of two kinds of $5nm and$30nm-sized mesopores,with a large surface area ($834m2gà1,as calculated using the BET method)and pore vol-ume(1.95cm3gà1).Since Fe3O4particles,as observed in TEM im-age(Fig.1c),were larger than the small-sized mesopores($5nm), most of particles were located in the$30nm-sized mesopores. More rapid decrease of volume of large-sized pores($30nm)than that of small ones($5nm)also indicates the preference occupa-tion of Fe3O4in main large pores(Fig.2b).Although incorporation of Fe3O4in MSU-F-C induced distinct decrease of surface area (386m2gà1)and pore volume(0.59cm3gà1),all of above charac-terization of Fe3O4/MSU-F-C reveal that pore structure,morphol-ogy and physical properties for facial catalytic reaction were still maintained.

The XRD pattern of Fe3O4/MSU-F-C is shown in Fig.3a.All of the diffraction peaks were well indexed to the Fe3O4crystal structure (JCPDS number:88-0315),with small and broad diffraction peak around25°due to the amorphous carbon supports.The crystallite size of Fe3O4calculated from the XRD peaks,using Debye–Scherrer equation,was around15nm,which was well-matched with the average size of the Fe3O4particles in the TEM image.The magnetic behavior of Fe3O4/MSU-F-C was investigated by SQUID magnetom-eter at room temperature.The hysteresis loop of the Fe3O4/MSU-F-C in Fig.3b shows relatively high magnetic saturation value ($32emu gà1)and very small remanence($2.5emu gà1).Thus,it can be easily separated with permanent magnet and re-dispersed into solution quickly without severe aggregation.The very small remanence may be caused by a small fraction of unexpected large-sized Fe3O4particles,which exhibit weak ferrimagnetic prop-erty,though average particle size($15nm)of Fe3O4incorporated in MSU-F-C was smaller than superparamagnetic critical size ($25nm)(Liu et al.,2004;Yamaura et al.,2004).To con?rm the loading amount of Fe3O4,thermogravimetric analysis(TGA)was carried out up to700°C in air atmosphere(See Fig.S2in the supple-mentary data).After complete combustion of carbon supports,the content of residual reddish products(46.8wt.%)was slightly larger than that of Fe3O4because of the transformation of magnetite to hematite during the oxidation process.Therefore,considering this fact,the Fe3O4content in Fe3O4/MSU-F-C was$45wt.%,which was consistent with the expected value.The stepwise weight loss between350°C and550°C can be attributed to the catalytic com-bustion of carbon in the vicinity of Fe3O4nanoparticles(Ennas et al.,1999)and then complete burn off the remaining carbon, which is also observed in the TGA graph of c-Fe2O3loaded meso-porous carbon(Baikousi et al.,2012).

3.2.Catalytic activity of Fe3O4/MSU-F-C for oxidation of phenol and arsenic

The potential of Fe3O4/MSU-F-C for the removals of phenol and arsenic was examined in comparison with commercial iron oxides, such as magnetite(Fe3O4),hematite(a-Fe2O3)and goethite (a-FeOOH).In order to test the catalytic activity for the Fenton reaction,the time–dependent oxidation of phenol and As(III)was monitored in the presence of the catalysts and H2O2under acidic conditions.The total concentration of arsenic(arsenite,As(III)+ arsenate,As(V))in solution was measured during the process to monitor the removal of arsenic due to adsorption onto the surface of the catalysts.

Fe3O4/MSU-F-C exhibited exceptional performance as a Fenton catalyst compared to the other iron oxides.As shown in Fig.4a, Fe3O4/MSU-F-C degraded phenol by approximately95%in4h; whereas,the commercial iron oxides showed only20–30%remo-vals during the initial stage mainly attributable to adsorption.In the absence of H2O2,the phenol removal by Fe3O4/MSU-F-C was similar to those by commercial iron oxides(See Fig.S3in the

1232J.Chun et al./Chemosphere89(2012)1230–1237

supplementary data).The catalytic oxidation of As(III)into As(V) was also pronounced,with Fe3O4/MSU-F-C showing2–3-fold high-er activity than the commercial iron oxides(Fig.4b).The decrease in the total arsenic concentration([As tot])due to adsorption was insigni?cant with only0.1g Là1of material.In addition,Fe3O4/ MSU-F-C showed higher activity in oxidation of phenol and As(III) than commercial nanoparticulate Fe3O4(See Fig.S4,in the supple-mentary data),suggesting that the combination of iron oxide with mesoporous carbon foam may offer synergistic reaction routes for the catalytic oxidation of target compounds(Also see Section3.3).

A pulse radiolysis study(Kl?ning et al.,1989)have suggested that As(IV)is formed as an intermediate during the oxidation of arsenic by?OH.As(IV)can be converted into As(V)by either disproportion-ation or further oxidation by oxygen.

On the other hand,the stability of Fe3O4/MSU-F-C was examined by conducting multiple runs of experiments of phenol degradation reusing the catalyst under identical reaction conditions([Fe3O4-MSU-F-C]0=0.1g Là1,[H2O2]0=10mM,[Phenol]0=0.1mM,pH0= 3.0,reaction time=4h).Fe3O4/MSU-F-C was simply recoverable by a permanent magnet after each run(See the inset image in Scheme1).

3.3.H2O2utilization ef?ciency for oxidation of phenol and arsenic

A notable observation is that the superior catalytic activity of Fe3O4/MSU-F-C was not based on the accelerated decomposition of H2O2(Fig.5),indicating that Fe3O4/MSU-F-C may have a higher ef?ciency for converting H2O2into?OH compared to commercial iron oxides.Fe3O4/MSU-F-C decomposed H2O2by only10% (1mM;similar to commercial iron oxides;Fig.5a)when0.1mM phenol was almost completely removed(Fig.4a).Interestingly,this observation is in contrast to the behaviors of contaminant oxidation

Fig.1.(a)SEM image and(b)TEM image of MSU-F-C.(c)TEM image of Fe3O4/MSU-F-C.

(a)Nitrogen adsorption–desorption isotherms and(b)corresponding pore size distributions of MSU-F-C and Fe3O4/MSU-F-C.

Fe3O4/MSU-F-C.Parentheses indicate the peaks for crystalline Fe3O4(JCPDS number:88-0315).(b)The magnetic hysteresis K).

phenol and(b)arsenic(III)by Fe3O4/MSU-F-C catalyst and commercial iron oxides in the presence of H2O2:[Fe3O4-MSU-F-C] =[a-FeOOH]0=0.045g Là1;[H2O2]0=10mM;[Phenol]0=[As(III)]0=0.1mM;pH0=3.0.

Scheme1.Schematic representation for removal of arsenic and phenol using Fe3O4/MSU-F-C as a catalytic adsorbent.

of H2O2and iron dissolution during the oxidation of(a)phenol and(b)arsenic in the presence of iron oxide and H2O2:[Fe3O [Fe3O4]0=[a-Fe2O3]0=[a-FeOOH]0=0.045g Là1;[H2O2]0=10mM;[Phenol]0=[As(III)]0=0.1mM;pH0=3.0.

by iron oxide-loaded mesoporous silica reported in the previous study (Lim et al.,2006):the degradation rate of contaminant in-creased to the degree that the decomposition of H 2O 2was acceler-ated.From the results in Figs.4a and 5a,the H 2O 2utilization ef?ciency for the phenol removal (i.e.[Phenol]divided by [H 2O 2])was calculated as approximately 10%,although it is not an opti-mized value.The high H 2O 2utilization ef?ciency of Fe 3O 4/MSU-F-C appears to be attributable to the af?nity of contaminants for the mesoporous carbon support.The molecules of phenol or arsenic ad-sorbed on the mesoporous carbon foam are retained in close prox-imity to the active site of iron at which ?OH is generated,increasing the chance for the contaminant to be exposed to ?OH.The enhance-ment in the H 2O 2utilization ef?ciency has been also reported with silica–alumina-supported iron oxides (Pham et al.,2009).However,further research will be needed to elucidate the detailed mecha-nism for the high activity of this material as a Fenton catalyst.3.4.Effect of dissolved iron

The processes with heterogeneous Fenton catalysts do not only rely on the reactions that occur on the surface of the catalyst,but also on homogeneous reactions in the bulk phase by dissolved iron

released from the catalyst.The relative importance of the homoge-neous reactions depends on the type of catalysts and experimental conditions.Several reports have shown that the Fenton reaction by dissolved iron species signi?cantly contributes to the oxidation of the target contaminants in the catalytic processes using iron oxides (Li et al.,2007;Lan et al.,2008;Pariente et al.,2008;Gulshan et al.,2010).On the contrary,a few studies have reported a negligible ef-fect of the homogeneous reactions (Feng et al.,2003;Yuranova et al.,2004).In the present work,the concentration of iron eluted from Fe 3O 4/MSU-F-C was approximately 3M,and separate exper-iments showed that the oxidation of phenol and arsenic in the presence of 3M Fe(III)and 10mM H 2O 2was negligible (data not shown).In addition,the concentration of eluted iron was almost constant regardless of the catalyst used (Fig.5),which con?rms that the superior catalytic activity of Fe 3O 4/MSU-F-C is not due to homogeneous Fenton reactions by the dissolved iron species.3.5.Removal of arsenic by adsorption

As the dose of Fe 3O 4/MSU-F-C was increased,the decrease in the [As tot ]became signi?cant due to the adsorption of arsenic onto the catalyst surface (Fig.6a),simultaneously leading to a decrease

in

arsenic and oxidation of arsenic(III)by Fe 3O 4/MSU-F-C (a and b)and commercial iron oxides (c and d)in the presence [Fe 3O 4]0=[a -Fe 2O 3]0=[a -FeOOH]0=1.0g L à1;[H 2O 2]0=10mM;[As(III)]0=0.1mM;pH 0=3.0.

the[As(V)]in solution(Fig.6b).In the absence of H2O2,a negligible amount of arsenic(mostly As(III))was removed by adsorption (Fig.6a),which was consistent with the previous?ndings that As(III)was more mobile than As(V)in soils and would be unlikely to be adsorbed onto the mineral surfaces at the mineral–water interface(Manning and Goldberg,1997;Manning et al.,2002). These observations clearly indicated the removal process of arsenic by the Fe3O4/MSU-F-C/H2O2system proceeded via the preoxidation of As(III)into As(V),with the subsequent adsorption of As(V)onto the catalyst.Arsenic was also adsorbed onto the commercial iron oxides when the dose was increased(1g Là1),but their ef?ciencies were not comparable to that of Fe3O4/MSU-F-C(Fig.6c and d). Although the catalytic activity for As(III)oxidation into As(V)was different among the commercial iron oxides(Fig.6c),their adsorp-tion capacities for total arsenic species were shown similar(Fig.6d).

4.Conclusions

Fe3O4/MSU-F-C showed promise as a versatile material for appli-cation to the removal of toxic water contaminants,which exhibited strong magnetism as well as superior catalytic activity and adsorb-tivity.Fe3O4/MSU-F-C showed exceptional activity for oxidizing phenol and arsenic compared to commercial iron oxides without signi?cantly accelerating the decomposition of H2O2,which pro-vides a great advantage for the utilization of H2O2in the Fenton sys-tem.Arsenic was completely removed in the presence of Fe3O4/ MSU-F-C and H2O2by two steps,the oxidation of As(III)into As(V) and the subsequent adsorption of As(V)on the catalyst surface. Acknowledgements

This work was supported by Fundamental Technology Develop-ment Programs for the Future(2E22173-11-069)through the Kor-ean Institute of Science and Technology(KIST)and by Korea Ministry of Environment as‘The Converging Technology Project’(191-101-006)and as‘‘The GAIA Project(2012000550021)’’.This work was also?nancially supported by the second stage of the BK21program of Korea.

Appendix A.Supplementary material

Supplementary data associated with this article can be found,in the online version,at https://www.360docs.net/doc/b817158766.html,/10.1016/j.chemosphere. 2012.07.046.

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