Photocatalytic activity of metal oxide nanoparticles prepared by electrical arc discharge method in water

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1 Phototlyti tivity of metl oxide nnoprtiles prepred y eletril r dishrge method in wter ALI AKBAR ASHKARRAN 1,*, AHOUD GHORANNEVISS 1 1 Plsm Physis Reserh Center Siene nd Reserh Brnh, Islmi Azd University P.O. Box: , Tehrn IRAN * shkrrn@sriu..ir Astrt: e report novel, inexpensive nd one-step pproh for synthesis of metl oxide nnoprtiles using the novel eletril r dishrge method in wter. Importnt funtionl semiondutor nnostrutures suh s ZnO, O 3 nd ZrO 2 were prepred y this method nd evluted for phototlyti pplitions. The resulting nnostrutures were hrterized using X-ry diffrtion (XRD), trnsmission eletron mirosopy (TE), X-ry photoeletron spetrosopy (XPS) nd UV-Vis spetrosopy. O 3 Cui nnostrutures with 3 nm men prtile size were formed during the dishrge proess in wter. Dishrge etween zin eletrodes in wter leds to formtion of rod like nd semi spheril ZnO nnostrutures with 15-2 nm dimeter rnge. ZrO 2 nnoprtiles were formed using zironium eletrodes in wter. Photodegrdtion of Rhodmine B () shows tht the prepred nnostrutures in this method hve potentil ility for environmentl purifitions. Key-ords: Ar dishrge; DI wter; metl oxide nnostrutures; XRD; TE; XPS; Phototlyti tivity 1 Introdution Over the lst dede there hs een inresed interest in semiondutor nnoprtiles due to their potentil pplitions in phototlysis, gs sensors, solr ells, UV light-emitters, eletroni nd optil devies, fuel ells nd smrt mterils. [1-4]. Speifilly, muh ttention hs een drwn towrds their phototlyti properties euse of their pplitions in environmentl purifition nd deomposition of toxi nd orgni ompounds. A key requirement for improving the phototlyti tivity is to inrese the speifi surfe re nd enhne the rystllinity [5]. These requirements re met y rystlline nnostrutured mterils. Severl methods inluding hydrotherml [6], sol-gel [7], hemil vpor deposition (CVD) [8] nd sputtering [9] hve een used to prepre metl oxide nnoprtiles. For effiient phototlyti tivity, nnomterils need to e rystlline, tht is, should e grown t high tempertures or t very slow rtes. In generl, different synthesis routes of nnostrutures usully result in morphous strutures ut, eletril r dishrge in wter hs the dvntge in this regrd s it produes selfrystllized nnostrutures due to high temperture used y joule heting. oreover, ompred with other tehniques, eletril r dishrge in wter is n ttrtive method euse of simpliity of experimentl set up, lk of need for omplited equipments, low impurity, less prodution steps leding to high-throughput nd ost-effetive proedure to generte high yield of nnoprtiles. Also the simpliity of this method llows sling up for mss prodution. The erly works y r dishrge method in liquids were sed on prodution of roneous nnostrutures suh s CNTs [1-13], SCNTs, S-CNHs [11] nd nno-onions [13]. In pst few yers, few ppers hve een pulished regrding synthesis of metl nd metl oxide nnostrutures suh s os 2 [14], CuO nd Cu 2 O [15], Ag [16, 17], Au [18, 19], O 3 [2] nd ZnO [21] y r dishrge in liquids. In the present study, we report simple, inexpensive nd one-step synthesis route for synthesis of metl oxide nnostrutures y r dishrge method in DI wter. e hve studied the effet of r urrent on size distriution nd the phototlyti tivity of the produed nnostrutures. The min dvntge of the present method is the diret formtion of nnostrutures from dishrge of metlli eletrodes within wter. 2 Experimentl detils 2.1 Synthesis of metl oxide nnostrutures The experimentl set up onsists of two min prts: high urrent DC power supply nd retor ISSN: ISBN:

2 inluding node, thode nd mirometer whih moves the node towrds the thode. In this work, 5 to 45 A urrent ws pplied etween two metlli eletrodes. The voltge ws dropped to out 2 to 3.5 V during the r formtion while the urrent ws fixed to desired mount. Both the node nd thode were wire shped, 1 mm in dimeter nd hd 99.9% purity. Initilly, we ring the two eletrodes into touh leding to smll ontt ross setion nd thus to high urrent density. Then we seprte them from eh other nd s result the metl is lted from the node nd then ondensed in wter nd forms different nnostrutures. 2.2 Chrteriztion Anlysis of the rystlline strutures ws performed y XRD diffrtometer (X'pert Philips) with wvelength of Cu Kα rdition in 2Ө rnge from 1 to 8 y.5 se-1 steps. UV-Vis spetrosopy of the smples ws tken out y Lmd 95 spetrophotometer (Perkin Elmer) from 2 nm to 11 nm wvelengths. TE nlysis ws performed y LEO 912 AB instrument t 2 kev elerting energy y deposition of nnoprtiles onto the opper grid t room temperture. XPS nlysis ws tken out y dul g-al node X-ry soure. A onentri hemispheril nlyzer (from Spes ompny model EA1 plus) ws employed to nlyze the emitted eletrons from the surfe. The energy xis ws lirted y djusting the ron peks t 285 ev. Surfe re of the nnoprtiles ws determined y Belsorp dsorption-desorption (BEL Jpn In.) instrument. Phototlyti tivity of the nnoprtiles ws mesured y photodegrdtion of with the initil onentrtion nd volume of 1-5 nd 3 ml respetively t the presene of 3 ml nnoprtiles solution. First the mixed nd nnoprtiles solution ws stirred in drk for 3 min to equilirte the dsorption/desorption etween dye moleules nd metl oxide phototlysts. Then it ws irrdited t room temperture y 125 lowpressure merury lmp with 254 nm strongest pek wvelength. The degrdtion rte ws mesured y UV Vis spetrophotometer t the mximum sorption wvelength of. DI wter ws supplied from illipore wter purifition system (Diret-Q-3) with 18.2 Ω-m (.55 µs) resistne. 3 Results nd disussion 3.1 XRD nlysis of the produts XRD results for s prepred smples when using zin, tungsten nd zironium eletrodes in wter demonstrte formtion of rystlline ZnO, O 3 nd ZrO 2 phse whih is depited in Fig. 1(-). The otined spetr re in good greement with the , nd stndrd rds from the JCPDS. In this method the s prepred prtiles re usully rystllized due to high tempertures used y joule heting. Anneling the extrted powder t 5 o C in ir for 1 hour did not result in ny remrkle hnges in the intensity or position of the. The single rystlline size fter het tretment ws pproximtely onstnt ompred with efore nneling. Intensity (.u.) Intensity (.u.) Intensity (.u.) (1) (2) (2) (111) (12) (22) (21) (121) (221) (1) (2) T (11) T 2θ (degree) 2θ θ (degree)( : onolini T: Tetrgonl nneled s prepred (12) 2θ (degree) (11) (13) T nneled s prepred (112) (2) (21) (4) nneled s prepred (22) ISSN: ISBN:

3 Fig. 1. XRD pttern of s prepred nd nneled nnostrutures t 5 o C for 1 hour () ZnO, () O 3 nd () ZrO 2. XPS nlysis To e sure out the omposition of the produts we performed XPS nlysis. Fig. 2 (-) shows the XPS dt for the s-synthesized smples. Counts (.u.) Zn 2p1/2 Zn 2p3/2 O Auger O 1s Fig. 2. XPS nlysis of s prepred () ZnO, () O 3 nd () ZrO 2 nnostrutures. From XPS spetrum the inding energies of Zn 2p 1/2 nd Zn 2p 3/2 for the s prepred ZnO re nd 123 ev, 4f 7/2 nd 4d 5/2 re 35.9 nd ev nd Zr 4p, Zr 3d, Zr 3p 3/2, Zr 3p 1/2 nd Zr 3s for the s prepred ZrO 2 nnoprtiles re 53.7, 28.5, 181.5, 333, nd ev, respetively. In ddition wek C 1s pek t 285 ev is oserved due to mient ir ontmintion. The rtio of the totl re under oxygen to metl peks determines oxygen to metl rtio t the surfe. This vlue for ZnO, O 3 nd ZrO 2 ws 1.2, 3.5 nd 2.2, respetively. The exess rtio from the expeted vlues is due to dsored oxygen t the surfe of the smples. Counts (. u.) Counts (.u.) O 1 O Auger O 4 Binding energy (ev) 8 Binding Energy (ev) 6 O 1S Zr 3S 4 4 Binding energy (ev) Zr 3p 1/2 Zr 3p 3/2 C 1s C C 1S 2 2 Zr 3d 2 Zn 3s Zn 3p Zn 3d Zr 4p 3.3 TE studies The shpe nd size distriution of nnostrutures were hrterized y TE. Fig. 3 (-) illustrtes typil morphologies of ZnO, O 3 nd ZrO 2 nnostrutures otined t threshold r urrents. This is the urrent whih the metlli eletrodes strt to evporte. O 3 nnostrutures with ui geometries oserved t 25 A r urrent while rodlike s well s semi spheril ZnO nnostrutures were found in TE imges of ZnO smples t 5 A r urrent. In generl, O 3 nd ZnO tend to form ui nd rod-like strutures due to their lttie geometries. By inresing the r urrent the size f the nnostrutures inreses too (Fig. 3(d-f)) nd semi spheril nd spheril nnoprtiles were formed. The presene of high temperture region nd DI wter in the retor leds to the formtion of temperture grdient nd fst ondenstion proess. In ft rpid ooling of the produts freezes their shpe nd redues the growth rte of the reted nulei nd they hve not enough time to form ui or rod-shpe strutures efore stiliztion. Therefore the numer of semi spheril nnoprtiles is more thn ui nd rod-like nnostrutures in higher r urrents whih is due to temperture inrese t higher r urrents nd fster ondenstion. In the se of ZrO 2 we oserved tht the prtiles re nnosized nd spheril. This mens tht the spet rtio is lose to 1 nd size of the nnoprtiles is etween 7 nd 3 nm nd the verge dimeter is 21 nm. 3.3 Phototlyti tivity mesurements Phototlyti tivity of metl oxide nnostrutures depends on their surfe re. In order to evlute ISSN: ISBN:

4 ADVANCED RESEARCH in PHYSICS nd ENGINEERING their tivity we first determined the tive surfe re of the nnostrutures. BET nlysis gives the surfe re of the nnostrutures out 34, 26 nd 44 m2/g for ZnO, O3 nd ZrO2, respetively. e f Fig. 3. TE imges of () ZnO, () O3 nd () ZrO2 nnostrutures t minimum nd (d) ZnO, (e) O3 nd (f) ZrO2 nnostrutures t mximum eletril r urrents. Chnges in the sorption spetrum of under UV illumintion t different irrdition times for the smples mde t diffrent r urrents nd one smple s referene re illustrted in Fig. 4. No remrkle hnges in the onentrtion of the Rh. B solution were oserved in the sene of metl oxide nnostrutures. Therefore, deomposition of Rhodmine B only depends on the photoexittion of metl oxide nnostrutures. The onentrtion nd volume of ll smples were hosen t 1 m nd 3 ml respetively with 1:1 rtio of metl oxide to for ll mesurements. e hve mesured yield nd verge prodution rte of metl oxide nnostrutures y mesuring weight loss of the eletrodes nd durtion of the r proess to hieve sme onentrtion in ll smples. It ws oserved d ISSN: ISBN:

5 tht y inresing the irrdition time the mximum sorption pek dereses. This indites tht the onentrtion of is deresing t the presene of metl oxide nnostrutures nd UV illumintion. Ln(C/C) Ln (C/C) Ln (C/C) Rhodmine B 45 A 25 A A 15 A 1 A 15 A 5 A Fig. 4. Chnges of Rhodmine B onentrtion under UV illumintion for () ZnO, () O 3 nd () ZrO 2 nnostrutures. Though ll kineti urves ehve similrly, for the se of the lrger prtiles photodegrdtion rte is less. This n e due to higher surfe re in smples with smller size. Compring the phototlyti tivity of produed nnostrutures revels tht smples with higher surfe re hve higher phototlyti effiieny. In ddition ompred with ommeril TiO 2 phototlyst (Deguss P25) our smples show similr trend. Ln (C/C) O3 ZnO ZrO O 3 ZnO ZrO2 Fig. 5. Comprison the phototlyti tivity of produed metl oxide nnostrutures. 4 Conlusion e hve prepred metl oxide nnostrutures in one-step synthesis proess y high urrent eletril r dishrge of metl eletrodes in DI wter. XRD nd XPS results indited formtion of ZnO, O 3 nd ZrO 2 phse. TE imges reveled ui O 3 nd rod-like s well s semi spheril ZnO nnostrutures. The prtile size ws found to inrese with n inrese in the r urrent. Phototlyti tivity of produed nnostrutures demonstrted tht y inresing UV illumintion time, the mximum sorption pek nd onentrtion of dereses in the presene of metl oxide nnostrutures. In ft, derese of onentrtion for ZrO 2 ws found to e more pronouned thn the ZnO nd O 3 whih ws due to inresed surfe to volume rtio. ISSN: ISBN:

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