Preparation and visible light photocatalytic activity of Bi 2 O 3 /CaO photocatalysts

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1 Rec Kinet Mech Ct (2010) 99: DOI /s Preprtion nd visible light photoctlytic ctivity of Bi 2 O 3 /CO photoctlysts Limin Song Shujun Zhng Received: 2 June 2009 / Accepted: 20 September 2009 / Published online: 6 Jnury 2010 Ó The Author(s) This rticle is published with open ccess t Springerlink.com Abstrct To utilize visible light more efficiently in photoctlytic rections, Bi 2 O 3 /CO photoctlysts were prepred by mechnicl mixing method nd chrcterized by X-ry diffrction (XRD) nd UV vis spectroscopy. UV vis spectroscopy results showed tht the photoctlysts hve wide bsorption bnd in the rnge of visible light. The photoctlytic ctivities of obtined Bi 2 O 3, CO, nd Bi 2 O 3 /CO smples were evluted by methylene blue degrdtion under visible light irrdition. It ws found tht the Bi 2 O 3 /CO smple exhibited the highest photoctlytic ctivity. Keywords Photoctlysts Bi 2 O 3 /CO A mechniclly mixing method Visible light irrdition Methylene blue Introduction In recent yers, lrge number of investigtions hve focused on semiconductor-bsed photoctlysts becuse of their wide pplictions in solr energy conversion nd environmentl purifiction [1 9]. Photoctlytic degrdtion hs proven to be promising technology for the removl of vrious orgnic pollutnts in wstewter for its mny ttrctive dvntges, including the environmentl friendly feture, reltively low cost nd little energy consumption. However, the fst recombintion rte of the photogenerted electron/hole pirs hinders the commerciliztion of this technology [10]. Among vrious semiconductors employed, Bi 2 O 3 is known to be good photoctlyst for the degrdtion of severl environmentl contminnts [10 15] due to its high photosensitivity, which L. Song College of Environment nd Chemicl Engineering nd Tinjin Key Lbortory of Fiber Modifiction nd Functionl Fiber, Tinjin Polytechnic University, Tinjin, People s Republic of Chin S. Zhng (&) College of Science, Tinjin University of Science nd Technology, Tinjin, People s Republic of Chin e-mil: cbnk@yhoo.cn

2 236 L. Song, S. Zhng mens high driving force for the reduction nd oxidtion processes. For the more efficient utiliztion of Bi 2 O 3, efforts hve been mde to combine Bi 2 O 3 with other semiconductors hving different bnd energies since the coupling of two semiconductor prticles with different energy levels is useful to chieve effective chrge seprtion [11 13]. In this report, novel Bi 2 O 3 /CO photoctlyst ws investigted, which is highly ctive in the photoctlytic oxidtive decomposition of MB under visible light irrdition. Experimentl Synthesis nd chrcteriztion of Bi 2 O 3 /CO photoctlysts The Bi 2 O 3 /CO photoctlyst ws synthesized by simple precipittion clcintionmixture method. Aqueous solutions of C(NO 3 ) 2 4H 2 O or Bi(NO 3 ) 2 6H 2 O nd NOH were mixed together in 1:3 molr rtio under stirring. The mixtures were stirred for 20 min t room temperture. Afterwrds, the precipittes formed were centrifuged, wshed with de-ionized wter, nd dried t 373 K in ir for 3 h. The obtined powder ws clcined t 800 C for 6 h to produce crystlline mterils. Finlly, Bi 2 O 3 nd CO prepred seprtely were mechniclly mixed in fixed molr rtio to obtin the Bi 2 O 3 /CO photoctlysts. Chrcteriztion X-ry diffrction (XRD) ptterns of the smples were tken on Rigku D/mx 2500 powder diffrctometer by using Cu K rdition with the wvelength of Å nd recorded from 3 to 80 (2h). UV vis bsorption spectr were recorded in the rnge of nm on HP8453 UV vis spectrometer. The BET surfce res (S BET ) were mesured by N 2 dsorption t -196 C using n utomtic surfce re nd pore size nlyzer (Autosorb-1-MP 1530VP). S BET mesurements were performed using the fivepoint BET method. Photoctlytic decomposition of methylene blue The photoctlytic ctivity under visible light irrdition of the Bi 2 O 3 /CO smples ws evluted by using methylene blue (MB) s the model substrte. 250 ml MB (10 mg/l) queous solution nd 1.0 g of photoctlyst powder were mixed in qurtz photorector. Prior to photoctlytic rection, the photoctlyst suspension ws sonicted to rech dsorption equilibrium with the photoctlyst in the drk. The bove solution ws photoirrdited by using 300 W Xe lmp s light source under continuous stirring. A cut-off filter ws used in these experiments (k [ 400 nm). At defined time intervl, the concentrtion of MB in the photoctlytic rection ws nlyzed by using n UV vis spectrophotometer t 665 nm. Results nd discussion The powder XRD ptterns of the Bi 2 O 3, CO, nd Bi 2 O 3 /CO smples treted t 800 C re shown in Fig. 1. From the corresponding chrcteristic 2h vlues of the diffrction peks in Fig. 1 nd b, it cn be confirmed tht the s-prepred Bi 2 O 3 smple is identified

3 Preprtion nd visible light photoctlytic ctivity 237 Intensity(.u.) c b θ/degree Fig. 1 Powder X-ry diffrction ptterns of the () CO, (b) Bi 2 O 3, nd (c) Bi 2 O 3 /Co smples clcined t 800 C s monoclinic phse (ICDD PDF ), while the CO is cubic phse (ICDD PDF ). Fig. 1c shows the XRD ptterns of the Bi 2 O 3 /CO smple obtined by mechniclly mixing lone Bi 2 O 3 nd CO clcined t 800 C. From Fig. 1c, ll the diffrction lines re nice mtch for the XRD ptterns of lone Bi 2 O 3 nd CO. It cn be observed tht there re no impurities other thn the phse of Bi 2 O 3 nd CO in Fig. 1c. The verge crystllite size of the CO nd Bi 2 O 3 components of the Bi 2 O 3 /CO smples ws clculted using the Debye Scherrer eqution: D ¼ 0:94k=b cos h where D is the verge crystllite size in ngstroms, k is the wvelength of the X-ry rdition (Cu K, nm), b is the full width t hlf-mximum, nd h is the diffrction ngle. The clculted results re 28 nd 21 nm for the CO nd Bi 2 O 3 components, respectively. Fig. 2 presents UV vis bsorption spectr of the Bi 2 O 3, CO, nd Bi 2 O 3 /CO smples clcified t 800 C. The s-prepred CO smple exhibits no obvious opticl properties concerning the bsorption in the visible light rnge, which is different from the Bi 2 O 3 smple. The Bi 2 O 3 smple hs wide bsorption bnd in the rnge of nm. For the Bi 2 O 3 /CO smple, there exists wide bsorption bnd in the visible light rnge, which shows tht the photoctlyst cn exhibit the higher visible light ctivity. The photoctlytic ctivity of the prepred smples ws determined by the degrdtion of 10 mg/l MB queous solutions under visible light irrdition. MB shows mximum bsorption t bout 665 nm. Totl concentrtions of MB were simply determined by the mximum bsorption mesurement. The specific surfce re of the Bi 2 O 3, CO, Bi 2 O 3 / CO, nd P25 smples is 12, 39, 27, 45 m 2 g -1, in order. (The mole rtio of Bi/C is 0.25.) The decrese of the concentrtion of MB in queous solution fter 9.5 h under visible light irrdition in the presence of the Bi 2 O 3, CO nd Bi 2 O 3 /CO smples clcined t 800 C is shown in Fig. 3. From Fig. 3, the MB photolysis without photoctlysts only produces bout 10% decomposition of MB molecules, which cn be ccounted for the photosensitized cpbility of MB molecules. Under the sme rection conditions, the P25,

4 238 L. Song, S. Zhng Absorbnce c b Wvelength (nm) Fig. 2 UV-vis bsorption spectr of the smples. ()Bi 2 O 3,(b) CO, nd (c)bi 2 O 3 /CO clcined t 800 C Fig. 3 Concentrtion of MB fter 9.5 h under visible light irrdition () MB photolysis, (b) P25, (c) Bi 2 O 3,(d) CO, (e) Bi 2 O 3 /CO nd (f) dsorption of MB into Bi 2 O 3 /CO in drk MB Concentrtion (mg L -1 ) b c d e f CO nd Bi 2 O 3 smples exhibit low visible light photoctlytic ctivity for queous MB degrdtion. Their photodegrdtion efficiency is bout 32.8, 16.7 nd 53.8% (Fig. 3b d). The photodegrdtion efficiency of the Bi 2 O 3 /CO smple hs chieved 94.2% (Fig. 3e). However, the dsorption cpcity of MB into Bi 2 O 3 /CO is very smll in drk (Fig. 3f). In comprison with the seprte Bi 2 O 3 nd CO smples, the smple hs the highest photoctlytic ctivity towrd the MB degrdtion. The spectrl chnges during the photodegrdtion of MB medited by the typicl Bi 2 O 3 / CO smple (800 C, 6 h) under visible light irrdition re displyed in Fig. 4. In Fig. 4, there re two min bsorbnce peks t bout 290 nd 665 nm before the photoctlytic rection, which re ttributed to the bsorbnce of the phenyl ring nd the chromophore. During the photodegrdtion process, the two mjor bsorption bnds grdully shifted to bout 280 nd 590 nm, nd the intensities of the two bsorbnce peks decresed grdully with temporl evolution, which my imply the destruction of the MB structure over the Bi 2 O 3 /CO smple.

5 Preprtion nd visible light photoctlytic ctivity 239 Absorbnce h 1.0h 1.5h 2.5h 3.5h 5.5h 7.5h 9.5h Wvelength (nm) Fig. 4 Spectrl chnges during the photodegrdtion of MB medited by the Bi 2 O 3 /CO smple clcined t 800 C under visible light irrdition MB Fig. 5 Reusbility of Bi 2 O 3 / CO obtined by mechniclly mixing lone Bi 2 O 3 nd CO clcined t 800 C MB Concentrtion (mg L -1 ) Reusble Times To investigte the reusbility of the Bi 2 O 3 /CO photoctlyst, the Bi 2 O 3 /CO photoctlyst ws repetedly used 5 times under the sme experimentl conditions. Fig. 5 shows the reusbility results. According to Fig. 5, it is cler tht the concentrtion of MB in the photoctlytic rection grdully increses with incresing reuse times. The photoctlytic ctivity of Bi 2 O 3 /CO in the fifths experiment decreses by only 78%. XRD nlysis of the solid mteril remining fter five rection cycles reveled tht (BiO) 2 CO 3 hs been produced (Fig. 6). The result is the sme s in n erlier reference [16]. The slight structurl chnge my be min reson for the decrese in the photoctlytic ctivity of Bi 2 O 3 /CO. It is inferred tht the higher ctivity of Bi 2 O 3 /CO my be ttributed to the formtion of heterojunctions on its surfce in references [17, 18]. The electrons in the vlence bnd (VB) of Bi 2 O 3 cn be excited to the conduction bnd (CB) with visible light irrdition

6 240 L. Song, S. Zhng Fig. 6 Powder X-ry diffrction ptterns of () Bi 2 O 3 /CO, nd (b) dectivted mteril obtined fter five rection cycles Intensity(.u.) b θ/degree becuse Bi 2 O 3 hs high bsorption over the visible light rnge of nm. Therefore, mny vcnt holes re rendered in the VB of Bi 2 O 3, t the sme time, the electrons in the VB of CO cn be trnsferred to tht of Bi 2 O 3, which results in n effective seprtion of photogenerted electrons s well s holes, nd the holes in the VB of CO cn generte the photoctlytic oxidtion rections. Thus, the Bi 2 O 3 /CO photoctlyst cn effectively degrde MB by bsorbing the visible light. In summry, Bi 2 O 3 /CO photoctlysts were prepred nd the photoctlytic ctivity of s-prepred smples ws evluted. The electron trnsfer occurring inside the Bi 2 O 3 /CO photoctlysts ws demonstrted by performing the photoctlytic decomposition of MB under visible light irrdition. The photoctlysts exhibited higher photoctlytic ctivity towrds MB degrdtion thn pure P25, CO nd Bi 2 O 3 under visible light irrdition. Acknowledgment This work ws supported by Development Progrm of Science nd Technology of Tinjin (06TXTJJC14400). Open Access This rticle is distributed under the terms of the Cretive Commons Attribution Noncommercil License which permits ny noncommercil use, distribution, nd reproduction in ny medium, provided the originl uthor(s) nd source re credited. References 1. Fujishim A, Hond K (1972) Nture 37: Ashi R, Morikw T, Ohwki T, Aoki K, Tg Y (2001) Science 293: Fu XX, Yng QH, Wng JZ (2003) J Rre Erth 21: Miyuchi M, Tkshio M, Tobimtsu H (2004) Lngmuir 20: Nosk Y, Mtsushit M, Nishino J, Nosk AY (2005) Sci Technol Adv Mter 6: Irie H, Wshizuk S, Hshimoto K (2006) Thin Solid Films 510:21 7. Zeng J, Wng H (2007) J Phys Chem C 111: Liu JW, Chen G, Zhng ZG (2007) J. Hydrog Energy 32: Compton OC, Crroll EC (2007) J Phys Chem C 111: Hoffmnn MR, Mrtin ST, Choi W, Bhnemnn DW (1995) Chem Rev 95: Bessekhoud Y, Robert D, Weber JV (2005) Ctl Tody 101:315

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