Journl of Physics nd Chemistry of Solids ] (]]]]) ]]] ]]] Contents lists ville t ScienceDirect Journl of Physics nd Chemistry of Solids journl homepge: www.elsevier.com/locte/jpcs Friction nd chrcteriztion of photoctlytic ctivity of Fe 3 O 4 -doped CdS hollow spheres Wnqun Jing,, Cuifeng Jing, Zhen Co, Xinglong Gong,, Zhong Zhng c Deprtment of Chemistry, Hefei 2326, PR Chin CAS Key Lortory of Mechnicl Behvior nd Design of Mterils, Deprtment of Modern Mechnics, University of Science nd Technology of Chin, Hefei 2327, PR Chin c Ntionl Center for Nnoscience nd Technology, Beijing 18, PR Chin rticle info Article history: Received 3 Octoer 8 Received in revised form 2 Mrch 9 Accepted 29 Mrch 9 Keywords: A. Mgnetic mterils A. Nnostructures A. Semiconductors strct A new hollow sphere photoctlyst hs een fricted y comining Fe 3 O 4 with nnoprticulte CdS. Their microstructures nd photoctlytic ehvior were exmined y X-ry powder diffrction, trnsmission electron microscope, scnning electron microscope nd ultrviolet nd visile spectroscopy. These hollow nnostructures displyed superprmgnetism t room temperture. It showed higher ctivity on hollow sphere thn solid prticle s the ctlysis result. & 9 Elsevier Ltd. All rights reserved. 1. Introduction With the rpid development of dyestuff industry, printing dye wstewter hs lredy ecome one of the most significnt pollution sources of wter environment. This pollution source hs ttrcted much ttention of the society nd therefore extensive nd intensive reserch work ws ttempted to solve this prolem. For exmple, the ppliction of semiconductor ctlysts for degrdtion of orgnic pollution hs een key glol reserch hotspot recently [1 6]. It is minly ecuse this pproch does not generte ny secondry pollution y mking use of solr energy. Although possessing dvntges of stility nd low cost, the semiconductor ctlyst hs een proved to e of somewht limited use owing to the difficulties in seprting the products nd residul ctlysts [7]. The immoiliztion of semiconductor ctlyst hs therefore ttrcted lot of ttention. Inorgnic nnoporous mterils utilized s ctlyst supports for mny homogeneous ctlysts hve een successfully demonstrted [8 13]. Among vrious support mterils, mgnetic nnoprticles hve ecome the prominent cndidtes due to their unique properties nd potentil pplictions in vrious fields [14 ], especilly the regthering nd recycling of expensive ctlysts [7]. Mgnetic seprtion hs lwys een convenient method for seprting mgnetized species esily nd thoroughly from the multiphse system y simple mgnetic device without Corresponding uthors. Tel.: +86 55136765; fx: +86 55136419. E-mil ddresses: jingwq@ustc.edu.cn (W. Jing), gongxl@ustc.edu.cn (X. Gong). centrifugtion or filtrtion [7]. This pproch cn increse the durility of the ctlysts nd e operted esily in industry. For exmple, mgnetic nnoprticles utilized for removing nd recycling ctlysts hve een successfully demonstrted [7,21]. Unfortuntely, since mgnetic nnoprticles themselves hve strong mgnetic properties nd could esily ggregte together, pursuing stisfctory dispersion hs een criticl prolem [22]. To tckle this prolem, mgnetic hollow sphere ctlysts hve een fricted to improve dispersity y decresing ctlyst density [23]. Herein, friction of Fe 3 O 4 -doped CdS hollow sphere through simple wet-chemistry method is reported in this pper. Comprison of photoctlytic ctivity etween hollow nd solid nnoprticles hs een investigted. 2. Experimentl procedure 2.1. Preprtion of PSA@Fe 3 O 4 The mteril components include: cdmium cette (99.9%, CR), tetrhydrofurn (THF) nd mmonium hydroxide (NH 3 H 2 O, 25 28%) otined from Lingfeng Chemicl Regent Co., Ltd. of Shnghi. Ferric chloride hexhydrte (AR), sodium sulfite nhydrous (AR), thiocetmide (TAA, AR) nd methyl ornge (MO) were otined from Sinophrm Chemicl Regent Co., Ltd. All sustnces were used without further purifiction. The PSA@Fe 3 O 4 composites were prepred y simple wetchemistry method reported previously [24]. In typicl synthesis, PSA ws dispersed in lend solution with volume rtio of 2:1 22-3697/$ - see front mtter & 9 Elsevier Ltd. All rights reserved. doi:1.116/j.jpcs.9.3.14
2 W. Jing et l. / Journl of Physics nd Chemistry of Solids ] (]]]]) ]]] ]]] (V ethnol :V wter ¼ 2:1) nd 5 ml of FeCl 3 6H 2 O (.6 mol/l) which hd een purged with nitrogen for min to remove ll trces of oxygen tht ws dded. After stirring for min, N 2 SO 3 (.1 mol/l) queous solution ws grdully dded under stirring, followed y dropwise ddition of NH 3 H 2 O to djust the ph vlue to 8. The mixture ws stirred for 3 h t 65 1C under nitrogen tmosphere. After eing seprted y mgnetic field, the PSA@Fe 3 O 4 precipitte ws otined. 2.2. Preprtion of Fe 3 O 4 -doped CdS hollow spheres The synthesis of mgnetic ctlyst is s follows: typiclly, the s-prepred mgnetic sustrte prticles were dissolved in 4 ml of Cd(CH 3 COO) 2 2H 2 O (.5 mol/l) solution. 3 mmol/l of thiocetmide ws then dded.the mixture hd very cler rection with grdully deepened yellow colour, indicting the formtion of CdS. The mixture ws then stirred for 12 h t 65 1C. The coting process ws repeted twice. Finlly, the PSA@Fe 3 O 4 -doped CdS composites were seprted. The composite prticles were converted to Fe 3 O 4 -doped CdS hollow cpsules fter eing soked in THF. Susequently, the resulting hollow spheres were wshed with wter nd ethnol, then, they were dried t 5 1C for 4 h under vcuum. 2.3. Photoctlytic testing of the otined Fe 3 O 4 -doped CdS hollow cpsules The photoctlytic ctivity of the smples ws mesured y the decomposition of MO in n queous solution. The UV light ws generted y 4 W high-pressure hydrrgyrum lmp. Prior to irrdition, the suspension contining powdered ctlyst (3 mg) nd fresh queous solution of MO ws sonicted for 1 min. Given irrdition time intervls, series of queous solutions in certin volume were collected nd seprted y mgnetic field to remove the ctlyst composites. The photoctlytic performnce of the ctlyst ws evluted y monitoring the visile sornce (t l mx ¼ 463 nm) chrcteristic of the trget MO through UV vis spectroscopy using Shimdzu UV-241PC spectrometer. 2.4. Chrcteriztion 3. Results nd discussion The crystl structures of the prepred composites were oserved y the XRD mesurement. A typicl XRD pttern of PSA@Fe 3 O 4 is shown in Fig. 1, in which the diffrction peks correspond to Fe 3 O 4 [25]. It cn e oserved tht chrcteristic pek ppers t 2y ¼.31 for PSA [26]. FromFig. 1, it cn e deduced tht the composites re composed of crystlline Fe 3 O 4 nd CdS, while diffrction peks cn e indexed to typicl ulk cuic CdS with the cell prmeters ¼ 5.46 Å. This is consistent with the stndrd vlue for ulk cuic CdS (JCPDS 8-19). When the composites were treted in THF, the chnge of the chrcteristic peks of Fe 3 O 4 nd CdS cnnot e oserved. The prticle size of the shell is roughly estimted s 3 nm with the Scherrer s eqution [27], while in ccordnce to SEM, the shell is out 35 45 nm. Tht is ecuse Scherrer s eqution gives the originl size, while ggregtion exists in the SEM. No diffrction peks from other crystlline forms re detected, which demonstrtes tht these hollow Fe 3 O 4 -doped CdS smples hve high purity nd crystllinity. The Fe 3 O 4 -doped CdS hollow sphere ws further sujected to TEM nd SEM nlysis (Fig. 2). The TEM imge in Fig. 2 shows tht the mgnetite nnoprticles occupy only frction of the volume of PSA core. Compring Fig. 2 with Fig. 2, it is cler tht CdS hs een successfully coted on the PSA@Fe 3 O 4 composite. The hollow structure of the spheres is clerly reveled from the TEM imge shown in Fig. 2c compred with Fig. 2. It is evident tht there is strong contrst difference in ll of the spheres with drk edge nd right center, confirming their hollow structure [28]. The roken spheres (rrows point to) otined from SEM (Fig. 2d) indicte hollow structures further. Thiocetmide, nonionic precursor, ws chosen s the strting mteril. The S 2 ions, produced with slow speed in lkline solution nd under the het tretment results in the slow growth of the nnocrystl CdS [29,3]. Therefore, homogeneous CdS shell ws otined. We speculte tht the PSA core ws dissolved in THF forming hollow sphere. CH 3 CSNH 2 þ 2OH CH 3 COO þ NH 4 þ þ S 2 Nitrogen dsorption desorption isotherms re mesured to determine the specific surfce re nd pore volume of the Fe 3 O 4 - doped CdS hollow microspheres, nd the corresponding results X-ry powder diffrction (XRD) ptterns of the products were otined with Jpn Rigku D/Mx-gA rottion node X-ry diffrctometer equipped with grphite monochromtized Cu K rdition (l ¼.154178 nm). Trnsmission electron microscopy (TEM) photogrphs were tken with Hitchi model H-8 trnsmission electron microscope t n ccelerting voltge of kv. Scnning electron microscopy (SEM) imges were explored with JSM-67F Field Emission, Scnning Electron Micronlyser. The nitrogen (N 2 ) dsorption/desorption isotherms t out 77 K were studied dispending Micromeritics, ASAP M system. The opticl sorption ws recorded y n ultrviolet visile (UV)-241(PC)S mnufctured y Shimdzu Corportion. The mgnetiztion curves (M H curve) of the smples were recorded with Physicl Properties Mesurement System supplied y the Quntum Design Corportion. The stility of the photoctlyst ws determined y mesuring the mount of cdmium in processed wter. The solution ws diluted nd the cdmium concentrtion ws determined y inductively coupled plsm tomic emission spectroscopy (ICP AES) (Atomscn Advntge supplied y the Thermo Jrrell Ash Corportion). Intensity (.u.) 1 B (111) A(2) A(311) B (2) B (311) A Fe 3 O 4 B CdS A(511) A(44) 3 4 5 6 7 2θ (degree) Fig. 1. X-ry diffrction ptterns of () PSA@Fe 3 O 4 ; () PSA@Fe 3 O 4 -doped CdS nd (c) Fe 3 O 4 -doped CdS hollow spheres. c
W. Jing et l. / Journl of Physics nd Chemistry of Solids ] (]]]]) ]]] ]]] 3 Fig. 2. TEM of () PSA@Fe 3 O 4 ; () PSA@Fe 3 O 4 -doped CdS nd (c) Fe 3 O 4 -doped CdS hollow spheres nd SEM of Fe 3 O 4 -doped CdS hollow spheres. Quntity Asored (cm 3 /g STP) 7 6 5 4 3 2 1. Adsorption Desorption.2.4.6.8 1. Reltive Pressure (P/P ) Fig. 3. Nitrogen dsorption desorption isotherm of the Fe 3 O 4 -doped CdS hollow microspheres. M (emu/g) 1-1 - -1 M (emu/g) 1-1 - -1 H (Oe) -5 5 1 H (Oe) -5 5 1 Fig. 4. Room-temperture mgnetiztion curve of () PSA@Fe 3 O 4 -doped CdS nd () Fe 3 O 4 -doped CdS prticles. re presented in Fig. 3. The isotherms re typicl type IV, which indictes the presence of mesoporous nd mcroporous mterils ccording to IUPAC clssifiction [31]. The BET surfce re nd pore volume of the hollow microspheres re 5.9 m 2 /g nd.23 cm 3 /g, respectively, which mens there re few smll pores on the surfce, tht llow the MO solution to come into the hollow sphere. The M(H) curves of the smples re shown in Fig. 4, in which the nnoprticles exhiit superprmgnetic ehvior without the oservtion of coercivity nd remnence. These fcts re relted to finite size nd surfce effects [32]. The superprmgnetic ehvior shows the potentil pplictions in mgnetic devices on the nnometer scle. The sturtion mgnetiztion of this mgnetite nnoprticles is 18 emu/g, which is igger thn the reported vlue 3.69 emu/g of 27 nm mgnetite nnoprticles [33]. Thus, the high sturtion mgnetiztion in this cse proly ttriutes to the ig size of Fe 3 O 4 nnoprticles.
4 W. Jing et l. / Journl of Physics nd Chemistry of Solids ] (]]]]) ]]] ]]] As 1.2 1..8.6.4.2. min 5min 1min 4min 1min 1min C/C (%) 1 9 8 7 6 5 4 3 3 4 5 6 4 6 8 1 1 wvelength (nm) Irrdition time (min) Fig. 5. (A) UV vis spectroscopy of MO t different times in the photoctlytic experiment nd (B) effect of illumintion time on the degrdtion of MO when using different ctlysts () PSA@Fe 3 O 4 -doped CdS nd () Fe 3 O 4 -doped CdS. According to previous results [1,4], CdS semiconductor cn exhiit ctlysis on orgnic dyes nd therefore reserch out the ctlysis of the mgnetic composite hs een performed. Photoctlytic ctivity of the resulting smples ws investigted on the degrdtion of MO in n queous solution. The reltion etween MO reduction rtio (C/C ) nd light ppliction time is shown in Fig. 5B. It hs een oserved tht the reduction of MO y PSA@Fe 3 O 4 did not occur to n pprecile extent without CdS nnoprticles, indicting tht CdS nnoprticles ply the role of ctlyst for the reduction of MO. As expected, enhnced photoctlytic properties of the hollow composite (Fig. 5B-) were oserved compring to tht of PSA@Fe 3 O 4 -doped CdS (Fig. 5B-). This fct cn e explined s follows. The ctlytic ctivity could e reduced due to decrese in the surfce re deduced y the collision nd mlgmtion of CdS prticles during the photoctlysis rection [34], while the possiility of prticle collision nd mlgmtion decreses in Fe 3 O 4 -doped CdS ctlyst ecuse of etter dispersion s result of smller density. Consequently, higher photoctlytic ctivity is otined. In Fig. 5B, the degrdtion percent etween 1 nd 1 min is devint. After preliminry nlysis, the most likely cuse of the devince is tht, fter 1 min irrdition, prt of photoctlyst egn to gther, which induced the irregulr photoctlysis plot line. On the other hnd, the smple hs een degrded 5%; hence, it is more difficult for the photoctlyst to e in collision with MO. In order to find the stility of the photoctlyst, the processed wter ws conducted ICP AES nlysis fter ctlysis rection. As result, it ws found tht out.1% CdS ws in the solution, which mens 99.9% CdS ws stle enough to sty ttched to the PSA@Fe 3 O 4. Oviously, the photodegrdtion of MO concentrtion is up to 75% which is chieved in the Fe 3 O 4 -doped CdS hollow spheres suspension fter 1 min irrdition. This novel mgnetic hollow sphere photoctlyst is expected to find pplictions in mny other industrilly importnt ctlytic processes. 4. Conclusion In conclusion, new mgnetic hollow sphere photoctlyst for degrdtion of orgnic dyes sed on mgnetite nnoprticles incorported in CdS nnoprticles hs een prepred. It ws found tht the s-prepred hollow composite displyed superprmgnetic property. The studies suggest higher photoctlytic ility on Fe 3 O 4 -doped CdS hollow prticles compred to solid prticles ecuse of lrger surfce re. 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