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Gyoten, Hisaaki

Ino, Daisuke

Maruo, Yuko

Takaoka, Tomoyasu

イノ, ダイスケ

ギョウテン, ヒサアキ

タカオカ, トモヤス

マルオ, ユウコ

丸尾, ゆうこ

行天, 久朗

高岡, 友康

猪野, 大輔

English

University of Miyazaki Academic Repository

Solar-UV Photo-oxidation from Arsenite toArsenate by using TiO_2 Photocatalyst言語: English出版者: University of Miyazaki, IRISH公開日: 2020-06-21キーワード (Ja): キーワード (En): Oxidation of arsenite, TiO_2suspension作成者: 丸尾, ゆうこ, 猪野, 大輔, 高岡, 友康, 行天, 久朗,Maruo, Yuko, Ino, Daisuke, Takaoka, Tomoyasu,Gyoten, Hisaakiメールアドレス: 所属: メタデータhttp://hdl.handle.net/10458/5173URLP-1 The 3rd Arsenic Symposium in Miyazaki, lAPAN 22-26 November 2012Solar-UV photo-oxidation from arsenite to arsenate by using Ti02photocatalystYuko Maruo\ Daisuke Ino l , Tomoyasu Takaoka', Hisaaki Gyoten 1Advanced Technology Research Laboratories (ATRL), Panasonic Corporation, 3-4 Hikaridai,Seika-cho, Soraku-gun, Kyoto 619-023 7 JapanAbstractNatural contamination of groundwater by arsenic has become a threatening problem in manyparts of the world. As(IlI) is predominant species in groundwater. However, As(I1I) can not beremoved efficiently by conventional method such as coagulation and adsorption. Thus. thesemethods usually require a preliminary oxidation to convert As(III) into As(V). since As(V) iseasily removed in contrast to removal of As(lII). We have investigated the oxidation of As(lll)into As(V) by employing TiOe suspension vvith LV irradiation. The concentration of As(Ill)decreased with increase in LV ilTadiation time. On the other hand, concentration of As(V)increased with decrease in the concentTation of As(HI). This results shows that photocatalyticreaction on Ti02 was responsible for oxidation ofAs(IIl).Keywords: Oxidation of arsenite, TiOe suspension.1. IntroductionPollution of groundwater by arsenic has beensignificant environmental problem. Arsenic is wellknown to be a toxic element. Elevated As in groundwateris predominantly caused by the minerals containingarsenic. Natural contamination of groundwater by arsenichas become a threatening problem in many parts of theworld. especially in areas ""here groundwater is the onlyor major drinking v,,'ater resource, Actually, exposure ofhuman body to arsenic through drinking b'Toundwatcr hasbeen reported from many countries such as Bangladesh',China and India.2 Arsenic mainly cxists in inorganic fonnand has main two oxidation state such as As(V) andAs(JIJ) in natural water. In groundwater, As(IIl) ispredominant speCIes in grounchvater, becausegroundwater has anoxic and reduced conditions.'The conventional methods for removal of arsenic frompolluted water arc coagulation and adsoll)tion on ironoxide or activated alumina.4 These methods usuallyrequire a preliminary oxidation to convert As(llI) intoAs(V). since As(V) is easily removed in contrast toremoval of As(IIl). Oxidation of As(IH) has beenachieved by using H20 L• NaOel or Ch.In this study, Ti02 photocatalyst was employed foroxidation of As(IU). Water treatment by employing Ti02photocatalyst is attracting widespread interest due toexcellent performance in pollutant destruction. Weinvestigated the oxidation of As(lll) into As(V) by usingTi02 photocatalyst.2. Experimental metbodChemical materials used in this study were TiOLpo\vder (P25. Degussa). NaAs02 was used as the sourceofAs(HI).Ti02 suspensions werc by thoroughly mixing 0.0 I g ofP25 TiCh powder in 100 mL of ultrapure water solution.This mixed solution was ultrasonicated tor at least 1 hour,followed stirred at 30011)]11 for I hour.Monochromatic UV source used in the oxidizingContact: Yllko Maruo, Advanced Technology Researcb Laboratories, Panasonic CorporationAddress:3-4 Hikaridai. Seika-cho"Soraku-gun, Kyoto 619-0237E-mail Address:maruo.Yllko@jp.panasonic.com. phone numher:+81-774-98-2517107The 3rd Arsenic Symposium in Miyazaki, JAPAN 22-26 November 2012experiments was obtained from the combination of axenon lamp (MAX30l, Asahi Spectra Co.,Ltd, Japan)and a band-pass filter. The wavelength of themonochromatic UV was A= 350 nm with a full width athalf maximum of 10 nm. This monochromatic UV sourcewas irradiated onto a batch reactor vessel filled with a 5ml sample solution which involves As(III) at theconcentration of 1000 Ilg/L. Power density of the UVwas 1 mW/cm2 at the bottom of a reactor vessel. To fairlyevaluate an effect of inherent adsorption of As(IIl) ontothe surface of Ti02, the UV irradiation was started twohours later from the time when photocatalyst and As(IIl)were mixed. Quantitative analysis of As(IJI) wereperformed by using a high performance liquidchromatography and inductively coupled plasma coupledwith mass spectrometer system.3. Results and discussionThe highest photocatalytic activity of P25 Ti02 isobtained in the form of Ti02 suspension with treatedwater. Due to a high affinity of P25 Ti02 to aqueoussolution, Ti02 nanoparticles are thoroughly dispersed inthe suspension.Figure 1 shows a result of TiOz photooxidation ofAs(IJI). Horizontal axis represents the irradiation time ofUV, and vertical axis means the concentration of As(IlI)measured by the HPLC/TCP/MS. There was a smalldecrease of concentration at the UV irradiation time of 0mins. This is due to the inherent adsorption of As(ITI)onto the surface of photocatalystDTadiation time (mins)Figure 1 The change in concentration of As(IlI)and As(V) with irradiation time.With increase of the UV irradiation time from 0 to 8mins, an exponential decrease of the As(ITI)concentration was observed. It is obvious that thedecrease of As(Tll) concentration is attributed to thephotooxidation of As(Tll) occurred by Ti02photochemistry. On the other hand, concentration ofAs(V) increased with decrease in the concentration ofAs(ITI). The change in concentration of As(ITI) and As(V)indicated that photoreaction of Ti02 was responsible foroxidation ofAs(III) to As(V).As(JIl) was oxidized through three potential reactions inthe TiOz and UV system. Hydroxy radicals, trapped holesand superoxide radicals, which are generated by thephotoreaction on Ti02, participate in oxidizing reactionof As(III). Oxygen also plays important role, sinceoxygen is a photogenerated electron scavenger to givesuperoxide radicals which can oxidize As(IlI) to AS(V).5The other oxidant is OH radicals which produced by thereaction of water molecules with trapped hole. Aspreviously discussed, oxidation by OH radicals isdominant for oxidation ofAS(IJI).64. ConclusionWe investigated the oxidation of As(lIl) by using Ti02suspension for efficient removal of arsenic ingroundwater. In the Ti02 and UV system, theconcentration of As(lIl) decreased with increase inirradiation time. On the other hand, concentration ofAs(V) increased with decrease in that of As(llT). OHradicals generated by TiOz photoreaction was mainlyoxidizing agent for oxidation of As(III). This resultsshows that treatment by Ti02 is effective method forpreliminary oxidation of arsenic involved ingroundwater.5. ReferencesI Watanabe, C. (200 I). Environmental arsenic exposurein Bangladesh: Water versus extra-water intake of arsenic,Environ. Sci. 8, 459-466pp2 Roychowdhury, T., Tokunaga H., Uchino, T., andAndo, M., (2005). Effect of arsenic-contaminatedirrigation water on agricultural land soil and plants inWest Bengal, India, Chemosphere, 58, 799-81 Opp3 Fields, K., Chen, A., and Wang, L.(2000). Arsenicremoval from drinking water by coagulation/filtrationand lime softening plants, EPA-60012-79-1094 Kartinen, E.O., and Martin, C.J., (1995). An overviewof arsenic removal processes, Desalination, 103, 79-88pp5 Lee, H., and Choi, W, (2002). Photocatalytic oxidationof arsenite in Ti02 suspension: kinetics and mechanisms,Environ. Sci. Teehnol. 36, 3872-3878pp6 Dutta, P., Pehkonen, S., Sharma, v., and Ray, A.,(2005). Photocatalytic oxidation of As(IlI): Evidence ofhydroxyl radicals, Environ. Sci. Technol. 39,1827-1 834pp108

Solar-UV Photo-oxidation from Arsenite to Arsenate by using TiO_2 Photocatalyst

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Solar-UV Photo-oxidation from Arsenite to Arsenate by using TiO_2 Photocatalyst

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