JOURNAL OF ENVIRONMENTAL SCIENCES 47 (2016) Available online at ScienceDirect.

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1 JOUNL OF ENVIONMENTL SCIENCES 47 (2016) ville online t ScienceDirect Synthesis of TiO 2 visile light ctlysts with controllle crystlline phse nd morphology from Ti-ering electric rc furnce molten slg Yng Li 1,2, Lulu Liu 1, Min Guo 1,, Mei Zhng 1 1. School of Metllurgicl nd Ecologicl Engineering, University of Science nd Technology Beijing, Beijing , Chin 2. The Stte Key Lortory for efrctories nd Metllurgy, School of Mterils nd Metllurgy, Wuhn University of Science nd Technology, Wuhn , Chin TICLE INFO BSTCT rticle history: eceived 25 ugust 2015 evised 4 Novemer 2015 ccepted 12 Novemer 2015 ville online 24 Mrch 2016 Keywords: Ti-ering electric rc furnce molten slg Crystlline phse Morphology TiO 2 TiO 2 visile light ctlysts with different crystlline phses nd morphologies were synthesized from titnium-ering electric rc furnce molten slg (Ti-ering EF slg) y using simple cidolysis process. The effects of the ph of the HCl solution, liquid to solid rtio ( L/S, HCl solution to the residue rtio, ml/g) nd cidolysis time on the micro-morphology nd crystlline phse of s-prepred TiO 2 photoctlysts were systemticlly investigted. The results indicted tht with decresing ph in the HCl solution nd incresing L/S, the crystlline phse nd micro-morphology of the otined TiO 2 nnostructures tended to trnsform from ntse type TiO 2 with sphericl nnoprticle structures to rutile type TiO 2 with needle-like nnorod structures. The cidolysis time hd little influence on the crystlline phse ut gret impct on the size of the otined TiO 2. The growth mechnism of TiO 2 from Ti-ering EF slg during the cidolysis process ws lso discussed. In ddition, the influence of L/S on the photoctlytic properties of the synthesized nnostructured TiO 2 ws studied. The results showed tht the photodegrdtion efficiency for hodmine B solution could rech 91.00% in 120 min when the L/S ws controlled t 50: The eserch Center for Eco-Environmentl Sciences, Chinese cdemy of Sciences. Pulished y Elsevier B.V. Introduction The ppliction of photoctlysis for environmentl pollution tretment hs ttrcted considerle ttention for mny yers. Titnium dioxide (TiO 2 ) is the most widely used photoctlyst for contminted wter nd ir ecuse of its exceptionl opticl nd electronic properties, strong oxidizing power, nontoxicity, nd chemicl stility (Growsk et l., 2012). However, TiO 2 photoctlysts with different morphologies hve minly een prepred y chemicl regents such s TiCl 4 (Di Pol et l., 2008; Lee nd Yng, 2005, 2006; Pottier et l., 2001), TiOSO 4 (Prk et l., 1996; Wng et l., 2013), titnium isopropoxide (Syrov et l., 2014), tetrutyltitnte (Zhou et l., 2011), using vrious pproches. This pproch is not suitle for prcticl industril pplictions due to its high cost. Therefore, synthesizing TiO 2 photoctlysts using low-cost rw nturl mterils nd effective methods to meet the requirements for photodegrding pollutnts in wstewter nd polluted ir is still ig chllenge. Tskiridis et l. (2011) synthesized ntse type TiO 2 nno-powders Corresponding uthor. E-mil: guomin@ust.edu.cn (Min Guo) / 2016 The eserch Center for Eco-Environmentl Sciences, Chinese cdemy of Sciences. Pulished y Elsevier B.V.

2 JOUNL OF ENVIONMENTL SCIENCES 47 (2016) from red mud sulfte leching solution, suggesting tht it my e possile to otin nnostructured TiO 2 from ll Ti-ering mterils. It should e noted tht there re rich minerl resources of vndium titnium mgnetite ore deposited in Chin, nd every yer millions of tons of titnium-ering slg is produced y the iron nd steel industry; thus it is worth pursuing the synthesis of nnostructured TiO 2 from Ti-ering slg. ecently, our reserch group proposed novel process to prepre nnostructured Fe-doped TiO 2 photoctlyst from titnium-ering electric rc furnce molten slg (Ti-ering EF slg) (Li et l., 2013, 2015). However, the photoctlytic performnce would e improved gretly if the crystlline phse nd morphology of the prepred TiO 2 photoctlyst could e controlled, since the properties of TiO 2 photoctlysts re closely relted to its crystlline phse nd morphology. Up to now, vriety of TiO 2 photoctlysts with different crystlline phses nd morphologies hve only een synthesized from chemicl regents (Li et l., 2006, 2008; Shen et l., 2008; Sun et l., 2011; Zhou et l., 2011). Therefore, synthesis of TiO 2 photoctlyst with controlled crystlline phse nd morphology from Ti-ering EF slg under mild tretment conditions will e the focus of this study. In this study, TiO 2 photoctlysts with different crystlline phses nd morphologies were synthesized from Ti-ering EF slg vi simple molten NOH tretment nd cidolysis process. The influence of tretment prmeters such s liquid to solid rtio ( L/S, HCl solution to the residue rtio, ml/g), ph of the HCl solution nd cidolysis time on the microstructure, morphology, nd specific surfce re of the otined TiO 2 ws studied in detil. In ddition, the photoctlytic properties of the s-synthesized TiO 2 were lso investigted. This study my open up n inexpensive nd convenient pthwy for synthesis of nnostructured TiO 2 photoctlysts. 1. Experimentl 1.1. Mterils The Ti-ering EF slg smples (Pnzhihu Steel, Sichun Province, Chin) were produced using vndium titnium mgnetite concentrte through direct reduction rection in rotry herth furnce, nd smelting seprtion in n electric furnce. ccording to our previous works (Li et l., 2013; Que et l., 2015), it is known tht tht the Ti-ering phses of the slg re nosovite solid solution (MgTi 2 O 5 or Ti 3 O 5 etc.) nd Mg 2 TiO 4, while the min impurity phses re Mgl 2 O 4 nd morphous metsilicte. The min components of the Ti-ering EF slg re shown in Tle 1. ll the chemicl regents employed were nlyticl grde (Sinophrm Chemicl egent Co. Ltd) nd distilled wter ws used throughout the experiments. Tle 1 Min chemicl compositions of the Ti-ering EF slg nd the residue (units: wt.%). Composition TiO 2 N 2 O l 2 O 3 MgO SiO 2 CO Fe 2 O 3 Ti-ering EF slg esidue esidue otined from molten NOH tretment nd wter leching process. The detiled process would e illustrted in Section m nd scn speed of 10 /min (XD, M21X, MC SCIENCE Co. Ltd., Jpn). The morphology nd microstructure of the smples were exmined y trnsmission electron microscopy (TEM, FEI, F20). The mount of ionic doping ws nlyzed y energy-dispersive X-ry spectroscopy (EDS, Zeiss, Supr-55). The texturl properties were nlyzed y N 2 dsorption t 77 K using n utomted dsorption pprtus (Micromeritics, SP 2010). The specific surfce re nd verge pore volume were clculted from the N 2 desorption isotherm employing Brunuer Emmett Teller (BET) theory. The sorption spectr of the smples were mesured y UV Vis spectrophotometer (Persee, TU-1901) Experimentl process Synthesis of TiO 2 photoctlysts The Ti-ering EF slg ws ground to out 120 mesh nd mixed with NOH homogeneously, with Ti-ering EF slg/ NOH mss rtio ( slg/noh, g/g) of 1:1.5, in nickel crucile. Then, the nickel crucile ws plced into muffle furnce nd heted to 700 C, holding for 1 hr with free ccess to ir. fter the molten NOH tretment process, the nickel crucile ws tken out rpidly nd then cooled t room temperture. Fig. 1 gives the XD pttern of the lkli fusion slg otined from molten NOH tretment. s shown in Fig. 1, fter the molten NOH tretment, the Ti-ering phses in EF slg converted to N 2 TiO 3 nd N(Mg,Ti)O 2. Menwhile, the impurity phses converted to their corresponding sodium slts such s NlO 2 or morphous N 2 SiO 3, respectively. Intensity (.u.). Smple chrcteriztion Chemicl compositions were nlyzed y inductively coupled plsm opticl emission spectroscopy (ICP-OES, TELEDYNE Leemn Ls). The phse structure ws investigted y X-ry diffrction using Cu Kα rdition (λ = nm) with 40 kv, θ ( ) Fig. 1 XD pttern of the lkli fusion slg otined from molten NOH tretment. XD: X-ry diffrction.

3 16 JOUNL OF ENVIONMENTL SCIENCES 47 (2016) Then, the lkli fusion slg ws ground to out 200 mesh nd leched in distilled wter severl times until the lechte ecme neutrl. The slurry ws filtered nd the residue ws dried in oven t 80 C for 24 hr. During this process, the wter solule sodium slts such s N 2 SiO 3 nd NlO 2 could e seprted from wter insolule sodium titnte slts (N 2 TiO 3 nd N(Mg,Ti)O 2 ) ccording to their different soluilities. So, the components left in the residue were minly sodium titnte slts s lso shown in Tle 1. This residue ws used s rw mteril to perform the cidolysis process for synthesis of TiO 2 photoctlysts. During the cidolysis process, 5 g of the residue ws mixed with wter homogeneously under fixed L/S in flsk. Concentrted HCl solution ws used to djust the ph. Then the mixture ws heted to 100 C, refluxing for certin time. Vigorous stirring ws mintined throughout the entire process. Susequently, the smple otined from the cidolysis process ws filtered to otin the residue. Finlly, the residue ws dried in n oven t 80 C for 24 hr nd clcined in muffle furnce t 450 C for 1 hr to prepre TiO 2 photoctlysts. The overll flow sheet of the process to synthesize TiO 2 photoctlysts from Ti-ering EF slg is illustrted in Fig. 2. It should e noted tht the cidolysis process ws the key step to determine the crystlline phse nd morphology of the nnostructured TiO 2 otined from the Ti-ering EF slg. Therefore, this study minly focused on the cidolysis process of sodium titnte under different conditions in order to elucidte the crystl growth mechnism of nnostructured TiO 2 clerly. NOH ( slg/noh =1:1.5) Titnium-ering EF slg lkli fusion slg Photoctlytic ctivity mesurements The photoctlytic ctivity of TiO 2 photoctlysts otined from Ti-ering EF slg with different L/S ws investigted y mesuring the photodegrdtion rte of hodmine B in queous solution. Photoctlytic rections under visile light irrdition were crried out in qurtz glss rector equipped with mgnetic stirrer nd collimted light source. For the visile light irrdition experiment, 500 W xenon lmp ws used s the light source, nd cutoff filter ws used to lock the UV light (<350 nm). 5 g s-prepred TiO 2 nd 200 ml hodmine B queous solution (5 mg/l) were plced into the rection vessel. O 2 ws continuously uled into the solution for 30 min efore switching on the lmp nd throughout the photoctlytic rections. t given intervls of visile light irrdition, 5 ml smples were withdrwn from the solution nd the ctlyst ws seprted from the solution y filtrtion. Quntittive determintion of hodmine B in the solution ws performed y mesuring its sorption with UV Vis spectrophotometer. The photodegrdtion efficiency (η) ws evluted s: η ¼ 0 t 100% ð1þ 0 where, 0 nd t re the concentrtions of hodmine B t the eginning nd fter illumintion for time t, respectively. 2. esults nd discussion During the cidolysis process, the rections tht occurred etween the residue nd HCl solution cn e regrded s liquid solid rections (Eqs. (2) (4)). The residue otined from the wter leching process might e dissolved in HCl solution nd then Ti ions would form TiO 2 crystl nuclei on the surfce of undissolved residue y heterogeneous nucletion. t the sme time, n ion exchnge rection would lso occur etween the remining undissolved residue nd H + to form hydrted Distilled wter, Electromgnetic stirring Wter, djust liquid-solid Concentrted HCl, djust ph vlue esidue Filtrtion lkli solution ecycling : rutile : ntse 50:1 eflux condensing, Electromgnetic stirring Filtrtion 75:1 esidue Drying, Clcintion 100:1 Nnostructured TiO 2 Fig. 2 Flow sheet of the process to synthesize TiO 2 photoctlysts from Ti-ering electric rc furnce slg θ ( ) Fig. 3 XD ptterns of TiO 2 photoctlysts otined with different L/S with refluxing for 6 hr t ph 0.22.

4 JOUNL OF ENVIONMENTL SCIENCES 47 (2016) Tle 2 Phse compositions nd texturl properties of the smples otined with different L/S. L/S Constitute (%) BET surfce Morphology res (m 2 /g) ntse utile 50: Nnoprticles clusters 75: Urchin-like structures 100: Urchin-like structures TiO 2, which cn e converted to TiO 2 y drying nd clcintion. The two competitive rections, nmely, the dissolution rection nd H + ion exchnge rection, would hppen simultneously. Therefore, the experimentl prmeters including L/S,pHnd rection time plyed importnt roles in determining the key rection during the cidolysis process, which influenced the crystlline phse nd morphology of the otined TiO 2. N 2 TiO 3 þ 2H þ H 2 TiO 3 þ 2N þ N 2 TiO 3 þ 4H þ TiðOHÞ 2þ 2 þ 2N þ þ H 2 O ð3þ TiðOHÞ 2þ oiling 2 þ H 2 O H 2 TiO 3 þ 2H þ 2.1. Effect of liquid to solid rtio Fig. 3 shows the XD ptterns of TiO 2 otined with different L/S. It cn e seen from Fig. 3 tht series of strong diffrction peks indexed to ntse type TiO 2 ppered when the L/S ws fixed t 50:1, suggesting tht only ntse type TiO 2 could e synthesized t this vlue of L/S. With L/S incresing to 75:1, mixtures of ntse nd rutile type TiO 2 with higher frction of rutile were otined. Further incresing L/S to 100:1, the rutile phse ecme predominnt while ntse ws the minority phse, indicting tht ntse type TiO 2 would e pt to chnge to rutile type TiO 2 with incresing L/S. The rutile rtio (F ) of ech smple ws estimted from XD intensity dt sed on the following formul (Li et l., 2008): F ¼ I ði þ 0:886I Þ ð5þ where, I nd I re the integrted intensities of the ntse (101) nd rutile (110) diffrction peks, respectively. ccording to formul (5), the contents of different phses in the products ð2þ ð4þ could e clculted from the corresponding XD ptterns, nd the results re listed in Tle 2. s shown in Tle 2, the content of ntse type TiO 2 decresed from 100% to 22% while tht rutile type TiO 2 incresed from 0% to 78% s the L/S incresed from 50:1 to 100:1, indicting tht ntse type TiO 2 would chnge to rutile type TiO 2 spontneously with incresing L/S. Fig. 4 shows the TEM imges of s-synthesized TiO 2 from Ti-ering EF slg with different L/S. It cn e seen in Fig. 4 tht single crystlline TiO 2 nnoprticles ggregted together to form nnoprticle clusters, nd the verge dimeter of the nnoprticles ws out 5 nm with L/S t 50:1. However, when the L/S incresed to 75:1 nd 100:1, the TiO 2 nnoprticle clusters chnged to structures resemling se urchins, with mny nnorods on ech urchin-like prticle (Fig. 4 nd c). Specificlly, the nnorods were single crystlline nd grew long the [100] direction. The surfce re properties of the smples were determined from the N 2 dsorption/desorption isotherms s shown in Tle 2. It is indicted tht rutile type TiO 2 ws pt to grow into urchin-like structures while ntse type TiO 2 preferly formed nnoprticle clusters. In ddition, when the L/S ws controlled t 50:1, the synthesized TiO 2 nnoprticle clusters showed the lrgest specific surfce re of m 2 /g compred to tht with urchin-like structures (117.6 nd m 2 /g), which would led to etter photoctlytic properties for the otined TiO Effect of ph vlue of HCl solution Fig. 5 shows the XD ptterns of TiO 2 otined in HCl solution with ph vlues rnging from 0.52 to 5. It cn e seen tht the diffrction peks of ntse type TiO 2 ppered prominently when the ph vlues were controlled t 0.52 or 0.22, suggesting tht only ntse type TiO 2 could e otined in HCl solution with ph vlues from 0.52 to However, on further decresing the ph to 5, some strong diffrction peks of rutile ppered together with those of ntse, indicting tht the product otined in the cidolysis process would chnge from ntse to rutile type TiO 2 spontneously with decresing ph. Fig. 6 shows the TEM imges of the TiO 2 photoctlysts otined t different ph in HCl solution. It is clerly seen tht urchin-like structured TiO 2 could e otined when the ph ws t 5, nd ech urchin-like prticle ws composed of c Fig. 4 TEM imges of TiO 2 photoctlysts otined with different L/S with refluxing time 6 hr t ph 0.22 of () 50:1, () 75:1, nd (c) 100:1. XD: X-ry diffrction; TEM: trnsmission electron microscopy.

5 18 JOUNL OF ENVIONMENTL SCIENCES 47 (2016) : rutile : ntse 5 Tle 3 Phse compositions nd texturl properties of the smples otined with different ph vlues. ph vlue Constitute (%) ntse utile BET surfce res (m 2 /g) Morphology Intensity (.u.) Urchin-like structures Nnoprticles clusters Nnoprticles clusters θ ( ) tiny nnorods with length out 20 nm growing long the [100] direction. s the ph incresed to 0.22 nd 0.52, the urchin-like structures were trnsformed to nnoprticle clusters (Fig. 6 nd c). The relted growth mechnisms will e discussed in Section 2.4. The phse compositions nd texturl properties of the smples otined t different ph vlues re shown in Tle 3. It is indicted tht reltively high ph vlues (higher thn 0.22) my led to the formtion of ntse type TiO 2 with nnoprticle cluster structures, while reltively lower ph vlues (lower thn 5) would led to mixture of TiO 2 phses (ntse nd rutile) with urchin-like structures. Moreover, the s-prepred TiO 2 smples with nnoprticle cluster structures showed lrger specific surfce res (304.7 nd m 2 /g) compred to those with urchin-like structures (146.6 m 2 /g), which would led to etter photoctlytic properties for the otined TiO Effect of cidolysis time 0.52 Fig. 5 XD ptterns of TiO 2 photoctlysts synthesized from HCl solution t different ph with refluxing time 6 hr nd L/S 50:1. Fig. 7 illustrtes the XD ptterns of TiO 2 photoctlysts synthesized with different cidolysis times. It cn e seen tht only diffrction peks indexed to ntse type TiO 2 ppered, suggesting tht ll the smples otined with different cidolysis times were ntse type TiO 2 only. Menwhile, the intensities of diffrction peks ecme stronger with the rection time incresing from 3 to 9 hr, indicting tht the degree of crystllinity of the otined smples ws improved with prolonged time. From the ove results, we could see tht the cidolysis time hd little influence on the crystlline phse ut gret impct on the crystllinity of the otined TiO 2. The TEM imges of the TiO 2 photoctlysts prepred with different cidolysis times re shown in Fig. 8. It cn e seen tht ll the smples contined TiO 2 nnoprticle clusters. The crystl size (D) cn e clculted ccording to Scherrer formul D ¼ kλ= ðβ cosθþ where, k = 0.9 is the shpe fctor, θ is the Brgg ngle, nd β is the full-width t hlf mximum (FWHM) in rdins. The verge dimeter of the TiO 2 nnoprticles incresed from 5.84 to 6.47 nm with prolonging of the cidolysis time from 3 to 9 hr, s shown in Tle Mechnism of crystlline phse trnsformtion nd morphology evolution ccording to the ove Eqs. (2) nd (3), the residue otined from the wter leching process could e dissolved in HCl solution nd then Ti ions would e surrounded y H 2 O, OH or Cl ion in the solution, forming n octhedrl structure (Eq. (3)). In ddition, n ion exchnge rection would occur simultneously etween the remining undissolved residue nd H + to form hydrted TiO 2 (Eq. (2)), which cn e converted to TiO 2 y drying nd clcintion. The decisive fctor for the two competing rections ws ph, nmely, the dissolution c Fig. 6 TEM imges of TiO 2 photoctlysts synthesized from HCl solution t different ph with refluxing time 6 hr nd L/S 50:1 of () 5; () 0.22; (c) 0.52.

6 JOUNL OF ENVIONMENTL SCIENCES 47 (2016) Intensity (.u.) : rutile : ntse 3 h 6 h Tle 4 Phse compositions nd texturl properties of the smples otined with different cidolysis time. cidolysis time (hr) Constitute (%) ntse utile Dimeter of crystlline size (nm) Morphology Nnoprticles clusters Nnoprticles clusters Nnoprticles clusters 9 h θ ( ) Fig. 7 XD ptterns of TiO 2 photoctlysts otined with different cidolysis times with L/S 50:1 t ph rection tended to occur in HCl solutions with lower ph. Therefore, in this study, the min ttention ws focused on the dissolution rection process to elucidte the mechnism of crystlline phse trnsformtion nd morphology evolution t ph vlues in HCl solutions (ph = 5, 0.22 or 0.53). It is known tht Ti ions dissolved in HCl solution will comine with nions to form six-fold coordinted monomer with n octhedrl coordintion structure, with the formul [Ti(OH) 2 Cl m (H 2 O) n ] 2 m, where m + n = 4, nd m depends on the cidity nd the mount of Cl ions in the solution (Phn et l., 2009; Zheng et l., 2001). In our study, the mount of Cl ions ws determined y the ph of the HCl solution, since ll the Cl ions were introduced the dded HCl. The formtion of TiO 2 with different crystlline phses strongly depends on the ssemly of octhedrl [Ti(OH) 2 Cl m (H 2 O) n ] 2 m species, which re the sic structurl units of oth the ntse nd rutile phses. s shown in Fig. 9, [Ti(OH) 2 Cl m (H 2 O) n ] 2 m octhedr linked y shring two equtoril edges to form chins long the c-xis, followed y cornershred onding mong chins, leds to the three-dimensionl frmework of the rutile phse (Fig. 9). The rrngement of [Ti(OH) 2 Cl m (H 2 O) n ] 2 m octhedr vi picl edge onding forms spirl chins, creting the ntse phse (Fig. 9B) (Li et l., 2015). The process y which [Ti(OH) 2 Cl m (H 2 O) n ] 2 m octhedr linked together to form hydrted TiO 2 cn e divided into two prts. First, the presence of quo nd hydroxo lignds in the coordintion sphere of this complex llowed condenstion y oltion, which involved the elimintion of quo lignds (the Cl ions eing more strongly ound groups), nd the formtion of dimers nd smll chins y shring of equtoril or picl edges. Second, when ll wter molecules were removed, further condenstion would proceed y n oxoltion rection with HCl elimintion nd formtion of oxo ridges mong the dimers or smll chins. This process llowed the removl of Cl ions from the octhedr nd yielded hydrted TiO 2 (Zheng et l., 2001). If the mount of Cl ions in solution ws lrger, the numer of Cl groups ound to the Ti 4+ complex center incresed. On the other hnd, the possiility of Ti 4+ groups coordinting with H 2 O decresed. In this cse, deoxoltion etween [Ti(OH) 2 Cl m (H 2 O) n ] 2 m octhedr is much more prole, while the oxoltion etween octhedrl structures is much less prole. Eventully, the decrese of H 2 Ogroupsconnected with Ti 4+ complexes would increse the corner-shred onding etween two [Ti(OH) 2 Cl m (H 2 O) n ] 2 m octhedr, resulting in the formtion of the rutile structure (Oh et l., 2009). So, the crystlline phse of the otined TiO 2 photoctlyst would e pt to trnsform from ntse to rutile type TiO 2 with decresing ph. In ddition, it should e noted tht the TiO 2 photoctlyst would chnge from ntse to rutile type TiO 2 spontneously with incresing L/S in our experiment. This phenomenon cn c Fig. 8 TEM imges of TiO 2 photoctlysts otined with different cidolysis times with L/S 50:1 t ph 0.22) of () 3 hr; () 6 hr; (c) 9 hr.

7 20 JOUNL OF ENVIONMENTL SCIENCES 47 (2016) Oltion Oxoltion -2H 2 O [Ti(OH) 2 Cl m (H 2 O) n ] 2-m Octhedron B utile-type Oltion -2H 2 O Oxoltion [Ti(OH) 2 Cl m (H 2 O) n ] 2-m Octhedron ntse-type Fig. 9 Formtion mechnism of ntse nd rutile from octhedrl complex formed in HCl solution. lso e interpreted y n nlysis similr to tht ove, since the mount of Cl ions would increse with incresing L/S when the ph of the HCl solution ws fixed t From the TEM mesurements, it ws shown tht the rutile type TiO 2 ws pt to grow into urchin-like structures ut ntse type TiO 2 preferred to grow into nnoprticle clusters. ccording to the literture (Li et l., 2009; Zheng et l., 2013), it ws known tht Cl ions in solution could ct s n structuredirecting gent since they preferentilly dhere to the side surfce of the -xis s cpping gents, which ply n importnt role in inducing growth long the (100) direction, while inhiiting growth long other directions (Beukenkmp nd Herrington, 1960; Phn et l., 2009). So, the effect of restrining the rdil growth ecme stronger with incresing mounts of Cl ions. Nmely, with incresing L/S or decresing ph, the trend of xil growth is more pronounced, resulting in the formtion of needle-like nnostructure Photoctlytic properties of TiO 2 photoctlysts otined in different L/S Fig. 10 shows the UV Vis sorption spectr of TiO 2 photoctlysts synthesized with different L/S. It cn e seen tht the sorption spectr of s-prepred smples hd some degree of red shift, implying tht the photoctlytic properties of synthesized TiO 2 could e improved y extending the spectrl sorption re. In ddition, the nd gp energies (E g ) cn e clculted y the following eqution: n αhv ¼ hv E g ð6þ where, h is Plnck's constnt, v is the frequency of light, is constnt, nd n is equl to 2 for n llowed indirect trnsition or 0.5 for n llowed direct trnsition (Zheng et l., 2015). For TiO 2 the trnsition is indirect nd therefore (αhν) 0.5 is plotted s function of hν, from which the nd gp energy could e otined y Tuc plot (Fig. 10). The nd gp energies were estimted y extrpolting stright line to the sciss from the plots, nd the results re shown in Tle 5. The results show tht the nd gp energies of TiO 2 showed no ovious trend with decresing L/S (2.77 to 2.54 ev) ut were ll nrrower thn tht of pure TiO 2 (3.20 ev), which might e ttriuted to the doping y different ions in the solution. From Tle 5 it is lso seen tht Fe nd Si were doped into the s-synthesized TiO 2 with different weight percentges, nd the doping ions could form dopnt level ner the vlence nd of TiO 2, reducing the nd gp energy of TiO 2. sornce :1 75:1 100:1 (hv) nm 416 nm nm ev 2.54 ev 2.77 ev Wve length (nm) hv (ev) Fig. 10 () UV Vis sorption spectr of TiO 2 photoctlysts otined in different L/S (other preprtion conditions: ph 0.22, time 6 hr); () (αhv) 0.5 re plotted s function of hv from which the nd gp energies re otined y Tuc plot B

8 JOUNL OF ENVIONMENTL SCIENCES 47 (2016) Tle 5 Bnd gp energies, surfce res nd mount of ionic doping of the TiO 2 photoctlysts otined with different L/S. L/S Bnd gp Energy (ev) BET surfce res (m 2 /g) mount of ionic doping (wt.%) 50: : : The influence of L/S on the photoctlytic ctivity of the otined TiO 2 is illustrted in Fig. 11. It cn e seen from Fig. 11 tht the sornce of hodmine B solution decresed mrkedly with prolonged illumintion time. Moreover, the mximum sorption wvelengths of the degrded solutions exhiited hypsochromic shifts to certin extent, which my hve resulted from the stepwise formtion of series of N-de-ethylted intermedites (Fu et l., 2008). Fig. 11 gives the photodegrdtion efficiencies of TiO 2 photoctlysts otined with different L/S nd the minerliztion rte of hodmine B. It is shown tht the photodegrdtion efficiency of the otined TiO 2 could increse from 67.62% to 73.00% nd 91.00% s L/S decresed from 100:1 to 75:1 nd 50:1, Fe Si respectively, which my e scried to the different crystl phses nd specific surfce res of s-synthesized TiO 2. Lrger specific surfce re is eneficil to the dsorption of oxygen toms to form ctive hydroxyl groups, resulting in enhncement of the photoctlytic ctivity (Shen et l., 2008). s shown in Fig. 4, the morphologies of s-prepred TiO 2 chnged from ntse type nnoprticle clusters to rutile type urchin-like structures when the L/S incresed from 50:1 to 100:1. Menwhile, the relevnt specific surfce re decresed from to m 2 /g (Tle 5), leding to n ccording decrese in the photodegrdtion efficiency. However, compred to the minerliztion rte of hodmine B under visile light (5.3%) without ctlyst nd the dsorption rte of TiO 2 synthesized with L/S t 50:1 in drk conditions (11.9%), the photodegrdtion efficiencies of the otined TiO 2 photoctlysts were much etter, indicting tht the s-prepred TiO 2 hdgoodphotoctlytic ctivity under visile light. 3. Conclusions In this study, nnostructured TiO 2 visile light ctlysts with different crystlline phses nd morphologies were synthesized from Ti-ering EF slg. The effects of experimentl prmeters including L/S, ph of the HCl solution nd cidolysis 50:1 75: s s s Wvelength (nm) Wvelength (nm) 100:1 c Photodegrdtion efficiency (%) Wvelength (nm) Time (min) dsorption rte Minerliztion rte 50:1 75:1 100:1 d Fig. 11 The photoctlytic ctivity of TiO 2 photoctlysts otined with different L/S (other preprtion conditions: ph 0.22, time 6 hr) (), (), (c) the sornce chnge of hodmine B with the synthesized TiO 2 ; nd (d) the photodegrdtion efficiencies of TiO 2 for hodmine B.

9 22 JOUNL OF ENVIONMENTL SCIENCES 47 (2016) time during the cidolysis process on the crystlline phse nd morphology of TiO 2 photoctlysts were systemticlly studied. It ws shown tht the crystlline phse nd micro-morphology of the otined TiO 2 nnostructures tended to chnge from ntse type TiO 2 with sphericl nnoprticle structures to rutile type TiO 2 with needle-like nnorod structures with decresing ph in the HCl solution nd incresing L/S. The degree of crystllinity improved oviously nd the dimeter of crystllite size incresed from 5.84 to 6.47 nm with prolonging of the cidolysis time from 3 to 9 hr. However, the influence of cidolysis durtion on the crystlline phse ws not ovious. Moreover, the otined TiO 2 photoctlysts with nnoprticle cluster structures showed lrger specific surfce res compred to those with urchin-like structures. In ddition, the photoctlytic properties of TiO 2 otined with different L/S were lso investigted. The photodegrdtion efficiency for hodmine B solution could rech 91.00% in 120 min when the L/S ws controlled t 50:1. cknowledgments Funding for the study ws supported y the Ntionl Bsic eserch Progrm of Chin (Nos. 2014CB643401, ) nd the Ntionl Nture Science Foundtion of Chin (Nos , nd ). EFEENCES Beukenkmp, J., Herrington, K.D., Ion-exchnge investigtion of the nture of titnium(iv) in sulfuric cid nd perchloric cid. J. m. Chem. Soc. 82 (12), Di Pol,., Cuflo, G., ddmo, M., Bellrdit, M., Cmpostrini,., Ischi, M., et l., Photoctlytic ctivity of nnocrystlline TiO 2 (rookite, rutile nd rookite-sed) powders prepred y thermohydrolysis of TiCl 4 in queous chloride solutions. Colloids Surf. Physicochem. Eng. sp. 317 (1 3), Fu, H.B., Zhng, S.C., Xu, T.G., Zhu, Y.F., Chen, J.M., Photoctlytic degrdtion of hb y fluorinted Bi 2 WO 6 nd distriutions of the intermedite products. Environ. Sci. 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