Available online at SciVerse ScienceDirect

J. Mater. Sci. Technol., 2013, 29(7), 639e646

Bismuth Modified Porous Silica Preparation, Characterization and

Photocatalytic Activity Evaluation for Degradation of Isoproturon

Anil Kumar Reddy Police, Srinivas Basavaraju, Durga Kumari Valluri, Subrahmanyam Machiraju*

Inorganic and Physical Chemistry Division, Indian Institute of Chemical Technology, Hyderabad 500607, India[Manuscript received August 29, 2012, in revised form October 12, 2012, Available online 8 April 2013]

* Corresp27160921005-030Journal oAll rightshttp://dx.

Porous silica prepared by using an acrylic emulsion has been impregnated with bismuth ion resulting in Bi2SiO5

species containing surface. The as-prepared materials have been characterized by X-ray diffraction spectroscopy(XRD), X-ray photoelectron spectroscopy (XPS), UVeVis diffuse reflectance spectroscopy (UVeVis DRS),scanning electron microscopy (SEM), energy dispersive analysis of X-ray (EDAX), transmission electronmicroscopy (TEM), Fourier transform infrared spectroscopy (FTIR) and N2 adsorption/desorption techniques.EDAX analysis confirms the penetration of bismuth ions into the framework of silica to form Bi2SiO5, which issubstantiated by XRD. The UVeVis DRS shows that the catalysts are optically active and XPS confirms theinclusion of bismuth into the framework of silica. FTIR spectra illustrate the formation of BieOeSi linkages inthe porous silica framework. SEM and TEM show the spherical morphology, whereas N2 adsorption/desorptionstudy confirms the porosity of the prepared materials. The photocatalytic activity of the material is evaluatedfor the degradation of isoproturon herbicide and it is found that the material is active as compared to thecommercial P-25 Degussa TiO2.

KEY WORDS: Acrylic emulsion; Emulsion polymerization technique; Porous silica; Bi2SiO5; Photocatalytic degradation; Isoproturon

1. Introduction

In recent years, heterogeneous photocatalysis is found to be apromising technology for the removal of toxic organic contam-inants from wastewater[1e3]. The semiconductor photocatalystswith various morphologies, microstructures are developed todate[4e10]. Among these materials, porous structured photo-catalysts are highly desirable because of their distinct charac-teristics such as large surface area and inner connected channels.Large surface area can supply more active sites and adsorb morepollutant. On the other hand, the inner connected channelsfacilitate the access of pollutant molecules to active sites and alsoimprove the distribution of photon energy over the porousframeworks. Consequently, the mass transfer and light utilizationefficiency of heterogeneous systems in photocatalytic reactionsare found to be enhanced.Mesoporous TiO2 is the most studied semiconductor photo-

catalyst[11e14]. However, the synthesis of mesoporous TiO2 with

onding author. Ph.D.; Tel.: þ91 40 27193165; Fax: þ91 401; E-mail address: subrahmanyam@iict.res.in (S. Machiraju).2/$ e see front matter Copyright � 2013, The editorial office off Materials Science & Technology. Published by Elsevier Limited.reserved.

doi.org/10.1016/j.jmst.2013.04.004

fine crystallinity remains a challenge. This is ascribed to the factthat the mesoporous framework of TiO2 easily collapses duringthermal treatment and is a requirement for removing the organictemplate that results enhanced crystallization of the TiO2

framework. In addition, the high temperature treatment is alsoan established method to eliminate the remnant pollutant in thepore channels for recovering its photocatalytic activity[15e17].Therefore, the creative design of a new porous structuredsemiconductor photocatalyst with high thermal stability isdesirable.In recent times, hybrid structure materials based on porous

silica have been proposed[18e22]. These materials as photo-catalysts offer several advantages, such as high electrochemicalstability, efficient electronehole separation and flexible selectionof semiconductors with desired band gaps for efficient lightabsorption. Bismuth ion modified silicates are reported recentlyfor the photocatalytic degradation of pollutants. Bi2SiO5 nano-sheets are synthesized by template free hydrothermal method andtested for the degradation of salicylic acid and benzene degra-dation[23]. However, they are nonporous and have low surfaceareas (4e6 m2/g) resulting in low photocatalytic activity ascompared to P-25 TiO2 sample. Zhang et al.[24] reported meso-structure Bi2SiO5 hallow microspheres by post synthetic modi-fication approach. They are tested for the rhodamine degradation.However, they have experienced a drastic decrease in the surfacearea of Bi2SiO5 as compared to the starting material SiO2. This is

Fig. 1 XRD patterns of low angle (a) and high angle (b): (a) SO, (b)BSO-0.5, (c) BSO-1, (d) BSO-3 and (e) BSO-5 samples.

Fig. 2 UVeVis DRS: (a) SO, (b) BSO-0.5, (c) BSO-1, (d) BSO-3, (e)BSO-5. Inset: UVeVis DRS of Bi2O3 and Bi2SiO5.

640 A.K.R. Police et al.: J. Mater. Sci. Technol., 2013, 29(7), 639e646

due to the decrease of the pore size and high crystallinity of theBi2SiO5 material. Also, Feng et al.[25] prepared hybrid Bi2SiO5

surface containing Si nanowire arrays for the degradation ofmethyl orange. In this, the surface of a silicon nanowire ismodified with bismuth in a dip coating and an etching method toproduce Bi2SiO5 surface modified Si nanowire. However, thisprocess is tedious and involves the usage of corrosive HF andcostly AgNO3. Also, these materials are crystalline and nonpo-rous in nature. Keeping this in view, in the present study, poroussilica with an average pore size (w6 nm) and high surface area(w200 m2/g) is prepared and the surface is modified with bis-muth up to 5 wt%. Thus obtained one resulted in the formationof porous silica modified with Bi2SiO5 species having goodthermal stability along with porous structure. Also, the preparedmaterials show photocatalytic activity for the degradation ofisoproturon herbicide.

Table 1 Physical properties of porous silica and Bi2SiO5 surfacecontaining silica

Catalyst Bi2SiO5 crystal size (nm)[from (311) plane]

Surface area (m2/g)

SO e 200.95BSO-0.5 e 170.65BSO-1 9.5 154.82BSO-3 11.6 145.37BSO-5 12.4 124.50

2. Experimental

2.1. Materials

All chemicals were used as such without any further purifi-cation. Isoproturon was obtained from Aldrich. NaF, butylacrylate, acrylic acid and methyl acrylate and Bi(NO3)3$5H2Owere from Loba Chemie Pvt. Ltd. Tetraethyl orthosilicate(TEOS) was obtained from Aldrich chemicals and titanium di-oxide P-25 (Anatase 80%, rutile 20%, surface area 50 m2/g andparticle size 27 nm) is from Degussa Corporation, Germany. Allthe solutions were prepared with deionized water (resistivity18 MU cm, DOC < 0.1 mg C L�1) obtained by using a Milliporedevice (Milli-Q).

2.2. Preparation of porous silica

The acrylic emulsion was prepared by emulsion polymeriza-tion technique[26]. The synthesis was carried out in a four-neckedglass reactor equipped with a glass stirrer, condenser and a gasinlet into which pure N2 gas was passed gradually and all thisequipment was kept in a water bath at 60 �C. Butyl acrylate,acrylic acid and methyl acrylate in the ratio (v/v) of42.1:5.3:52.6, respectively were added dropwise to this reactorcontaining 180 mL of deionized water over a period of 4 h undervigorous stirring. After adding all the ingredients, the mixture

Fig. 3 FTIR spectra: (a) SO, (b) BSO-3.

Table 2 Chemical compositions of the synthesized materials

Catalyst Bi (%) over silica(prepared)

Bi (%) over silica(from EDAX)

SO e e

BSO-0.5 0.5 e

BSO-1 1 1.68BSO-3 3 2.19BSO-5 5 2.82

A.K.R. Police et al.: J. Mater. Sci. Technol., 2013, 29(7), 639e646 641

was continuously stirred for another 1 h for complete polymer-ization that resulted in a whitish colored emulsion.The silica material was prepared by simple salt mediated

synthesis in which NaF was added and dissolved together withthe emulsion polymer at room temperature. The polymer (9.2 g)and NaF (3.0 g) were dissolved in 50 mL of deionized water.After complete dissolution of the above mixture, 15 g of thesilica precursor TEOS was added under vigorous stirring, afterwhich the stirring rate was lowered and continued for 6 h. Theprecipitation started almost immediately after the TEOS addi-tion. This mixture was transferred into an autoclave and cookedat 100 �C for 24 h. The product is filtered and washed with waterand calcined at 450 �C for 8 h.

2.3. Preparation of porous silica surface modified withbismuth ion

Porous silica surfacemodifiedwith bismuth ionwas prepared byan impregnatingmethod.Required amount ofBi(NO3)3$5H2Owasdissolved in deionized water and one or two drops of HNO3 wereadded for clear solution. To this solution silica prepared above wasadded and the solution was then subjected to heating to evaporatethe excess water. The powder sample was kept in oven for 12 h andcalcined at 650 �C for 6 h. Samples with 0, 0.5, 1, 3, 5 wt% bismuthover silica were prepared and labeled as SO, BSO-0.5, BSO-1,BSO-3 and BSO-5, respectively.

2.4. Characterization

The prepared catalysts were characterized by X-ray photo-electron spectroscopy (XPS), X-ray diffraction (XRD), N2

adsorption/desorption measurements, UVeVis diffused reflec-tance spectra (DRS), Fourier transformed infrared spectra(FTIR), scanning electron microscopy (SEM), energy dispersive

Fig. 4 N2 adsorption/desorption isother

analysis of X-rays (EDAX) and transmission electron micro-scopy (TEM) techniques.XPS spectra were recorded on a KRATOS AXIS 165 equip-

ped with MgKa radiation (1253.6 eV) at 75 W apparatus byusing MgKa anode and a hemispherical analyzer, connected to afive channel detector. The analysis was performed at roomtemperature. Prior to the analysis, the samples were evacuated athigh vacuum and then introduced into the analysis chamber.Survey and multiregion spectra were recorded at C1s photo-electron peaks. Each spectra region of photoelectron interest wasscanned several times to obtain good signal-to-noise ratios.The powder X-ray diffraction patterns were recorded on a

Rigaku diffractometer by using CuKa radiation (0.1540 nm),operated at 40 kV and 40 mA. The high angle X-ray diffracto-grams were recorded in the 2q range of 2�e80� with a 2q stepsize of 0.02� and the low angle X-ray diffractograms wererecorded in the 2q range of 0.5�e5� with a 2q step size of 0.01�.The XRD phases present in the samples were identified with thehelp of a powder diffraction file-international center fordiffraction data (PDF-ICDD). The average crystallite size wasestimated with the help of DebyeeScherrer equation from linebroadening.Surface properties of the catalysts were measured by N2

adsorption in autosorb 1C quantachrome physical adsorptionapparatus. The specific surface area and pore volume werecalculated applying BrunauereEmmetteTeller (BET) andBarretteJoynereHalenda (BJH) numerical integration methods,respectively. The BJH desorption model was used to calculatethe pore size distribution of the samples.The UVeVis DRS measurements were performed over the

wavelength range of 200e800 nm by using a GBC UVeVisible Cintra 10e spectrometer with an integration spherediffuse reflectance attachment. Samples were diluted in a KBrmatrix for palletization. The FTIR spectra of the catalysts wererecorded on a Nicolet 740 FTIR spectrometer (USA) by usingKBr self supported pellet technique in the frequency range of400e4000 cm�1.For the SEM analysis, samples were mounted on an aluminum

support by using a double adhesive tape, coated with gold inHUS-SGB vacuum coating unit and observed in Hitachi S-520SEM unit. Elemental analysis was carried out by Link, ISIS-300,Oxford, energy dispersive X-ray spectroscopy detector. TheTEM analysis was carried out on TECHNAI F12 Philips unitoperated at 80 kV with a filament current of 27 mA. The prep-aration of the samples for TEM analysis included sonication inan alcohol for 10 min and deposition on a copper grid.

ms: (a) SO, (b) BSO-3, (c) BSO-5.

Table 3 N2 adsorption/desorption measurements of the porous silicaand Bi2SiO5 surface containing silica samples

Catalyst Surface area(m2/g)

Average porediameter (nm)

Pore volume(cm3/g)

SO 200.95 6.8 0.506BSO-3 145.37 5.5 0.381BSO-5 124.50 4.3 0.338

642 A.K.R. Police et al.: J. Mater. Sci. Technol., 2013, 29(7), 639e646

2.5. Photocatalytic experiments

Isoproturon solution (1.14 � 10�4 mol/L) was freshly pre-pared by dissolving 25 mg isoproturon in 1 L double distilledwater. Dark (adsorption) experiments were carried out formonitoring the adsorption extent of the herbicide on the catalystsurface. For photo experiments, 50 mL isoproturon solution wastaken in a quartz reactor with known amounts of the catalyst. Thesolution was illuminated under 250 kW Mercury lamps.

2.6. Analysis

The isoproturon degradation was monitored by ShimadzuSPD-20A HPLC (high performance liquid chromatography)by using C-18 phenomenex reverse phase column (250 mm �4.6 mme5 mm) with acetonitrile/water (50/50, v/v) as mobilephase at a flow rate of 1 mL/min. The wavelength of the LCdetector was set to be 254 nm for the detection of isoproturon.The samples collected at regular intervals were filtered throughMillipore micro syringe filters (0.2 mm).

3. Results and Discussion

3.1. Characterization

3.1.1. XRD. The low angle XRD patterns of porous silica andbismuth modified porous silica samples are shown in Fig. 1(a).The BET surface area and the Bi2SiO5 crystal size of thesesamples are summarized in Table 1. All the samples show peaksat 2q < 1� indexed to (100), which indicates a highly orderedporous silica structure. The XRD patterns and the surface area ofthese samples indicate well ordered accessible pores, and verylittle influence of the added heteroatom (bismuth) on the poroussilica structure. However, the addition of the bismuth leads tolower surface areas as compared to pure silica (SO).

Fig. 5 SEM (a) and TEM (b)

The high angle XRD of the as-prepared porous silica surfacemodified with Bi2SiO5 (BSO) is shown in Fig. 1(b). Strong XRDpeaks of Bi2SiO5 are observed for the bismuth modified silicasamples at 5 wt% bismuth loading. These peaks indicate theformation of Bi2SiO5 phase which possesses an orthogonalstructure (JCPDS No. 360287). Also, the peaks corresponding toBi2O3 (marked with “x” in Fig. 1(b)) illustrate that small amountof un-interacted bismuth is present in the form of Bi2O3 on thesurface of silica. Peaks with the same position are observed for 1and 3 wt% bismuth loaded silica with lower intensity and for0.5 wt% bismuth loaded silica no peaks are detected. This mightbe due to the high dispersion and lower crystal size of Bi2SiO5

over silica that is beyond the detection limit of XRD[24,25,27,28].

3.1.2. UVeVis DRS. In order to find out whether the bismuthatoms are incorporated into the framework of silica or not, UVeVis DRS was carried out for the BSO samples. UVeVis DRS ofthe BSO samples are shown in Fig. 2. All the bismuth modifiedsilica samples show an intense band centered at 240 nm, and thisimplies the presence of a ligand to metal charge transferinvolving isolated Bi atoms (SieOeBieOeSi) in the structureof silica. In addition to this band, a shoulder band centered at330 nm is found for the sample BSO-5, and it indicates theexistence of another kind of bismuth species at high bismuthcontents, which may be assigned to the formation of polymericbismuth species (BieOeBi) which is in consistent with the re-sults obtained by XRD. From the above results it can beconcluded that at lower bismuth content, the bismuth species arewell incorporated into the structure of silica and exist as Bi2SiO5

whereas, at higher bismuth loading, they exist as Bi2O3 as wellas Bi2SiO5

[29e31].

3.1.3. FTIR. The influence of bismuth insertion into the frame-work of silica was investigated by recording the FTIR spectrum ofthe prepared samples in the range of 400e4000 cm�1. Fig. 3shows the FTIR spectra of the as-synthesized porous silica(SO) and Bi2SiO5 modified porous silica (BSO-3) in the range of400e1600 cm�1 for better clarity. The spectrum of pure silica(SO) shows three fundamental vibrations which give a band at450 cm�1, a weak band at 800 cm�1 and a strong one at about1100 cm�1. The latter is accompanied by a broad shoulder at1200 cm�1. These bands are attributed to different vibrationalmodes of SieOeSi links. Whereas, BSO-3 sample shows addi-tional bands at 550 and 640 cm�1 as compared to pure silicasample. The occurrence of these bands may be due to the latticedistortion caused by the bismuth insertion into the silica frame-work (since Bi3þ is approximately three times larger than Si4þ). In

images of BSO-3 sample.

Fig. 7 Photolysis (þ) and adsorption experiments of isoproturon so-lution on (:) SO, (B) BSO-0.5, (-) BSO-1, (,) BSO-3 and(C) BSO-5.

A.K.R. Police et al.: J. Mater. Sci. Technol., 2013, 29(7), 639e646 643

addition, the broadening of vibrational bands of silica at 1100 and1200 cm�1 is also caused by the formation of BieOeSi linkagesin the framework of silica[25,32,33].

3.1.4. EDAX. The insertion of Bi ions into the silica frameworkwas further substantiated by the EDAX analysis of the samples.The data obtained by SEMeEDAX of the Bi2SiO5 surfacecontaining silica are shown in Table 2. It can be clearly seenfrom the data that the amount of bismuth present on the surfaceof the material is less than the actual amount of bismuth added tothe respective material. During the calcination process, bismuthions penetrated through the lattice of silica there by forming aBi2SiO5 phase on the outermost layer of the silica surface.The remnant of bismuth on the surface formed Bi2O3 phaseon the surface of silica. The presence of Bi2O3 phase was notedin the XRD and UVeVis DRS of the samples. Hence, EDAXanalysis confirmed the insertion of bismuth into silica latticewhich resulted in the formation of Bi2SiO5 species surfacemodified porous silica.

3.1.5. Pore size distribution. In order to find out the effect ofbismuth modification on the surface area and porosity of thesilica samples, N2 adsorption studies were employed for the puresilica (SO) and Bi2SiO5 modified silica samples (BSO-3 andBSO-5). The N2 adsorption and desorption isotherms of thesamples are shown in Fig. 4. All the samples show Type-IVisotherms which are characteristics of porous materials. Inaddition, bismuth modification of silica does not lead to anycollapse in the porous structure of the silica materials. Up to 5 wt% bismuth loading no such significant change in the isotherms isobserved. This observation shows that the bismuth atoms are notoccluding in the porous channels. The surfaces measurementsvalues calculated from N2 adsorption/desorption isotherms aregiven in Table 3.

3.1.6. Morphology by SEM and TEM. SEM is used to deter-mine the morphology of the synthesized materials. An SEMpicture of the BSO-3 sample given in Fig. 5(a) is a typical onefor the porous metallosilicate and it shows the morphology ofspherical particles. It is clear that the particles are spherical inshape, although some agglomerates are detected. The sphericalnature of the prepared material is further confirmed by the TEMimages as shown in Fig. 5(b). Though the particles are indifferent sizes, most of them have particle size in the range of20e40 nm.

Fig. 6 Bi4f XPS: (a) BSO-3, (b) BSO-5.

3.1.7. XPS. In order to elucidate the chemical environment of thebismuth in the BSO samples, BSO-3 and BSO-5 catalysts aresubjected to XPS and the Bi4f spectra are shown in Fig. 6.Increases in the binding energy values of Bi4f7/2 and Bi4f5/2 areobserved for both BSO-3 (160.8 and 165.5 eV) and BSO-5(158.8 and 164.0 eV) samples as compared to the values ofbismuth in pure Bi2O3 (158.6 and 163.8 eV)[3]. The variation inthe binding energies may be due to the decrease of electrondensity around bismuth resulting by the interaction of the Bi withthe silica. This shows that the bismuth ion in BSO samples is instrong interaction with silica framework and exists as BieOeSi.However, both BSO-3 and BSO-5 samples show increase in thebinding energies, and BSO-5 sample shows small increase in thebinding energy as compared to pure bismuth. This might be dueto the formation of un-interacted Bi2O3 existing on the surface ofsilica. The formation of Bi2O3 phase is also observed in XRDand UVeVis DRS spectra of the respective samples. This resultshows that after optimum loading (3 wt%) excess bismuth formspolymeric bismuth oxide on the surface of silica.

3.2. Photocatalytic activity

Prior to photocatalytic experiments adsorption, photolysisstudies were carried out. The isoproturon solution was kept indark without catalyst for 10 days and no degradation wasobserved. Fifty milligram of the catalyst in 50 mL of isoproturon

Fig. 8 Photocatalytic degradation of isoproturon herbicide over (þ) SO,(:) BSO-0.5, (A) BSO-1, (C) BSO-3 and (-) BSO-5catalysts.

Fig. 9 Photocatalytic activity comparison of (C) BSO-3 and (B) TiO2

(P-25) catalysts for the degradation of isoproturon herbicide.

644 A.K.R. Police et al.: J. Mater. Sci. Technol., 2013, 29(7), 639e646

(1.14 � 10�4 mol/L) solution was allowed under stirring in dark.Aliquots were withdrawn at regular intervals and the change inisoproturon concentration was monitored by HPLC. Themaximum adsorption is reached within 30 min for all the cata-lysts prepared (Fig. 7). This illustrates the establishment ofadsorption equilibrium in 30 min which is chosen as the opti-mum equilibrium time for all the experiments. The photolysis(without catalyst) experiment was carried out under the solarlight and only 2%e4% of degradation was observed after 10 h ofsolar irradiation.Photocatalytic activities of the prepared BSO catalysts were

studied for the degradation of isoproturon herbicide. Prior tolight experiments adsorption experiments were carried out for30 min for better adsorption of the herbicide over the porousmaterial. About 35% of the herbicide was adsorbed on poroussilica (SO) and a decrease in the adsorption as compared to SOwas observed for BSO samples with increasing bismuth loading.Fig. 8 shows the degradation pattern of the isoproturon herbicideover Bi2SiO5 containing porous silica (BSO). Minor amount ofherbicide (w2%) is found to be degraded on pure silica whereas,and all the BSO samples show good photocatalytic activity forthe degradation of isoproturon. The enhanced photocatalyticactivity might have resulted from the formation of Bi2SiO5, inwhich (Bi2O2)

2þ layers and (SiO3)2� tetrahedra are slightly

distorted[24]. The distorted structure of (SiO3)2� tetrahedra may

Fig. 10 Recycling activity studies of BSO-3 sampl

be in favor of the separation of the photo generated holes andelectrons. Consequently, a higher degree of photocatalytic ac-tivity of the Bi2SiO5 is achieved. Photocatalytic activities of theBSO samples are found to increase with bismuth content andthen found to decrease with bismuth loading. Optimum photo-catalytic activity was observed for 3 wt% bismuth doped silica(BSO-3). The decrease in the activity at higher loadings might bedue to decrease in the surface area which in turn affects theadsorption of the herbicide on the porous material. It is seen fromFig. 8 that the adsorption of pure silica is more than that of otherBSO materials and the adsorption of BSO catalysts tends todecrease with increasing bismuth loading. This might be due tothe presence of nonporous Bi2O3 over silica. The formation ofBi2O3 and simultaneous decrease in the surface area of thematerial with increasing bismuth content over silica also areenvisaged by XRD and N2 adsorption and desorption experi-ments. Hence, crystalline Bi2SiO5 with moderate surface areapossesses more active sites resulting in higher photocatalyticactivity.Furthermore, the photocatalytic activity of the BSO-3

sample was compared with the commercial photocatalystDegussa (P-25) TiO2. After 30 min of adsorption, the amountof isoproturon adsorbed on TiO2 is very less (w8%) ascompared to BSO-3 sample (w28%) as shown in Fig. 9. Thelarge surface area of the porous BSO-3 possesses more activesites and adsorbs more pollutant. On the other hand, the innerconnected channels facilitate the access of reactant moleculesto active sites and also to improve the distribution of photonenergy over the porous frameworks. Hence, a better activityfor the porous BSO sample is envisaged as compared tononporous TiO2.In order to find out the stability of the BSO sample, a couple

of experiments are conducted over BSO-3 catalyst. The catalystrecovered from the 1st cycle is reused as it is subjected for thesecond cycle and the same is continued up to 5 cycles. The re-sults are shown in Fig. 10. Though, the activity of the catalyst isretained up to 5 cycles, a small decrease in the activity isobserved. This might be due to the formation of fragmentsformed in the degradation of herbicide that are being accumu-lated in the pores and on the surface of the catalyst. Therefore,from the above experimental results it can be concluded that thecatalysts are stable up to 5 cycles.

e for the degradation of isoproturon herbicide.

Scheme 1 Preparation of Bi2SiO5 containing porous silica and mineralization of isoproturon herbicide.

A.K.R. Police et al.: J. Mater. Sci. Technol., 2013, 29(7), 639e646 645

3.3. Formation of Bi2SiO5 containing silica and itsphotocatalytic activity

Bi2SiO5 phase containing silica preparation is shown in theScheme 1. Mesoporous silica is prepared by emulsion poly-merization technique. The prepared silica is impregnated withBi(NO3)3 solution to form bismuth modified silica. The as-pre-pared material is calcined in air. During the calcination processthe bismuth ions penetrate through the framework of silica andform Bi2SiO5 phase. The prepared material contains highlydispersed Bi2SiO5 nanocrystals on the surface of silica. Theporous silica containing Bi2SiO5 with high surface area providesbetter adsorption of herbicide in the vicinity of active Bi2SiO5.When the material is illuminated, the active e� and hþ separationoccurs in Bi2SiO5 semiconductor. The charge carriers formed

produce OH radicals in the solution. The hydroxyl radicals thusproduced attack on the isoproturon structure resulting in hy-droxylated compounds. The hydroxylated products further un-dergo successive attack of OH radicals resulting in themineralization of isoproturon.

4. Conclusion

A series of bismuth modified porous silica samples have beenprepared by impregnation method. The prepared catalysts arecharacterized by XRD, XPS, FTIR, UVeVis DRS, N2 adsorp-tion desorption, SEMeEDAX and TEM. Bismuth modified sil-ica results in the evolution of Bi2SiO5 crystallites on the surfaceof porous silica which is substantiated by XRD. The Bi2SiO5

crystallites are due to the penetration of bismuth ions into the

646 A.K.R. Police et al.: J. Mater. Sci. Technol., 2013, 29(7), 639e646

lattice of silica and this is confirmed by XPS, EDAX and FTIR.Also, UVeVis DRS of BSO samples shows optical absorption inthe near visible region. The porous silica serves as a supportto the Bi2SiO5 crystallites. Hence, the formed Bi2SiO5 species onthe surface of porous silica catalysts are proved to have goodphotocatalytic activity for the degradation of isoproturonherbicide. This work demonstrates the preparation of photo-catalytic active Bi2SiO5 material by using low cost silica andbismuth nitrate. This work paves the way to prepare bismuthmodified silica materials with high surface areas and porousstructures. Also, the surface of porous silica can be modified withvarious other semiconducting oxides and can be efficiently uti-lized for environmental as well as energy applications in thephotocatalysis.

AcknowledgmentThe authors PAKR and MS thank CSIR, New Delhi for

funding this work under Emeritus Scientist Scheme and alsothank Dr. Jae Sung Lee, POSTECH, South Korea for providingcharacterization data of the samples tested.

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