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1 Chemical Engineering Journal 222 (213) Contents lists available at SciVerse ScienceDirect Chemical Engineering Journal journal homepage: A new way to control the coordination of titanium (IV) in the sol gel synthesis of broom fibers-like mesoporous alkyl silica titania catalyst through addition of water Umar Kalmar Nizar a,b, Jon Efendi a,b, Leny Yuliati a, Dwi Gustiono a,c, Hadi Nur a, a Ibnu Sina Institute for Fundamental Science Studies, Universiti Teknologi Malaysia, 8131 UTM Skudai, Johor, Malaysia b Department of Chemistry, Universitas Negeri Padang, Jl. Prof. Hamka, Air Tawar, Padang, West Sumatera, Indonesia c Agency for the Assessment and Application of Technology, Jl. M.H. Thamrin No. 8, Jakarta, Indonesia highlights graphical abstract " The sol gel synthesis of mesoporous alkyl silica titania by addition of water. " Controlling the tetrahedral and octahedral coordination of Ti(IV) in alkyl silica titania. " The formation of mesoporous structure shaped like broom fibers alkyl silica titania. " The effect of the coordination of Ti(IV) in alkyl silica titania in polymerization of styrene. article info abstract Article history: Received 29 October 212 Received in revised form 3 February 213 Accepted 18 February 213 Available online 24 February 213 Keywords: Broom fibers-like mesoporous silica titania catalyst Sol gel method Octadecyltrichlorosilane Tetraethyl orthotitanate Polymerization of styrene In this research, the tetrahedral and octahedral coordination of Ti(IV) in alkyl silica titania has been successfully controlled by the addition of water in sol gel process. Octadecyltrichlorosilane (OTS) and tetraethyl orthotitanate (TEOT) were used as precursors. The effect of the addition of water on the local coordination of Ti(IV) was analyzed by using Fourier transform infrared (FTIR) spectrometer, diffuse reflectance ultra-violet visible (DR UV Vis) spectrometer, field emission scanning electron microscope (FESEM), X-ray diffraction (XRD) spectrometer and transmission electron microscope (TEM). It was demonstrated that water facilitate the formation of SiAOATi bond which is related to the tetrahedral Ti(IV). These materials exhibit the pattern of peak at the small angle of X-ray diffractogram and type IV shape adsorption desorption isotherms characteristic of mesoporous silica titania. The mesoporous structure shaped like broom fibers, arranged by lamellar structure like fibers with diameter size about 3 5 nm has been clearly observed by TEM. The catalytic activity of alkyl silica titania catalysts obtained was tested in polymerization of styrene in the presence of aqueous hydrogen peroxide. It showed that the presence of the tetrahedral Ti(IV) gave a beneficial effect in increasing the activity in this catalytic reaction. Ó 213 Elsevier B.V. All rights reserved. 1. Introduction Corresponding author. Tel.: ; fax: address: hadi@kimia.fs.utm.my (H. Nur). URL: (H. Nur). Silica titania is one of the important binary oxide materials and has been widely used for academic purpose and industry [1 5]. It has attracted widely interest due to their potential applications as the catalyst in various reactions from fine chemistry to /$ - see front matter Ó 213 Elsevier B.V. All rights reserved.

2 24 U.K. Nizar et al. / Chemical Engineering Journal 222 (213) photocatalytic removal of the water pollutant. The properties of silica titania materials depend on the structure, composition, and homogeneity of the prepared material [5]. It is generally accepted that there is a relationship between the type of local coordination of Ti(IV) in silica titania and their catalytic activity. The tetrahedral Ti(IV) species is believed to be more catalytically active compared to that of the octahedral Ti(IV) in titania [6]. To produce more tetrahedral Ti(IV) local coordination, silica titania material is usually prepared in confined environment, such as zeolite cavities, or silica matrix, and it improves the catalytic activity and stability of the silica titania catalyst. To improve the performance of silica titania catalyst, the sol gel process was proven to be convenience preparation method for such a catalyst with high dispersed tetrahedral Ti(IV), because it enables one to control the hydrolysis and condensation of silica and titania precursors to form SiAOATi bonding [7,8]. The process leads to the formation of bulk silica titania structure with homogeneously dispersed Ti(IV) in silica matrix and enhanced the surface properties of the oxides [3 8]. For such a purpose TEOS is commonly used as the silica precursor in the synthesis of a silica titania material [1,3,11 13]. Thus, the corresponding structural characterization of silica titania material was generally focused on the location, symmetry and bonding type of Ti(IV) in framework, extra framework, or on the surface of silica. Quantitative analysis of these characteristics would be a great importance, because it was closely related with the physical properties and catalytic activities of silica titania. The silica titania material has a hydrophilic surface and consequently, shows low affinity to contact with many hydrophobic organic substrates [8 1]. This low affinity may obstruct the mobility and transport of organic substrate to the close proximity of the active tetrahedral Ti(IV). Adjusting the silica titania surface opens more possibilities to be applied on the organic substrate. The sol gel technique provides an opportunity to tailor the chemical and physical properties of inorganic oxides by modifying their source materials and preparation conditions. Thus, organically modified silica titania, which was used in this research, was prepared via the sol gel technique by using octadecyltrichlorosilane (OTS) as an organic functionalized silane precursor. The SiAC bond does not participate in the hydrolysis and polycondensation steps. The surface of the resulting gel will be covered with long organic functional groups (R) and simultaneously surface enhanced the hydrophobicity with this long R chain. Polar and nonpolar regions can be produced on this organically modified silica titania [14,15]. Several stages generally involve in the synthesis of silica titania, such as hydrolysis of the precursors in ethanol water medium, and then followed by polycondensation of hydrolysis product into silica titania sol. The sol particles then aggregate into an alcogel network in aging time, and the dried product could be obtained at any desired temperature [14]. In this process, the amount of water added into the sol gel system is expected to play an important role in controlling the rate of hydrolysis and condensation stages due to the function of water as the reaction medium. As titania and silica precursors are in a mixture, there will be a possibility that titanium and silicon hydrolysis product to form SiAOASi, TiAOATi and SiAOATi bonds. Thus, the final products could be the mixture of titanium dioxide, silica and binary oxide silicaatitania depend on the number of hydrolysis product of both silica ( SiAOH) and titania ( TiAOH) and the possibility of both groups to collide and form SiAOATi bonds. Here, we demonstrated that the formation of tetrahedral Ti(IV) in alkyl silica titania material can be easily controlled by varying the amount of water added into the mixture of OTS and tetraethyl orthotitanate (TEOT) in toluene. The presence of high portion of the tetrahedral Ti(IV) gave a positive effect on styrene polymerization Table 1 The prepared alkyl silica titania. No. Alkyl SiO 2 ATiO 2 (n,m) a Mol fraction of water (%) Toluene (ml) 1 SiO 2 ATiO 2 (,) 2 SiO 2 ATiO 2 (6,) 6 3 SiO 2 ATiO 2 (22,1) SiO 2 ATiO 2 (41,1) SiO 2 ATiO 2 (6,1) SiO 2 ATiO 2 (74,1) SiO 2 ATiO 2 (87,1) 87 1 a The solid sample was labeled as SiO 2 ATiO 2 (n,m), in which n mol% water added into reaction mixture and m was ml toluene use as solvent. in the presence of aqueous hydrogen peroxide. Interestingly, the results showed silica titania had the mesoporous structure shaped like broom fibers, arranged by lamellar structure like fibers with diameter size about 3 5 nm. 2. Experimental 2.1. Synthesis of alkyl silica titania The synthesis of alkyl silica titania catalysts were carried out by a sol gel technique. Octadecyltrichlorosilane, OTS (Merck) and tetraethyl orthotitanate, TEOT (Merck) were used as silica and titania precursors, respectively. Deionized water and toluene (Merck) were served as sol gel reaction medium. To synthesize the alkyl silica titania materials, several mixtures containing OTS (1 mmol), TEOT (1 mmol) and toluene (1 ml) were prepared and homogenized in an ultrasonic bath. A different Transmittance / a.u Wavenumber / cm 1 SiO 2-TiO 2(87,1) 97 SiO 2-TiO 2(74,1) SiO 2-TiO 2(6,1) SiO 2-TiO 2(41,1) SiO 2-TiO 2(22,1) SiO 2-TiO 2(6,) SiO 2-TiO 2(,) Fig. 1. The FTIR spectra of the prepared alkyl silica titania catalysts.

3 U.K. Nizar et al. / Chemical Engineering Journal 222 (213) OH Peak Area / a.u SiO2-TiO2(,) SiO2-TiO2(6,) SiO2-TiO2(22,1) SiO2-TiO2(41,1) Tetrahedral fraction of Ti /% SiO2-TiO2(6,1) SiO2-TiO2(74,1) SiO2-TiO2(87,1) Fig. 2. The relationship between tetrahedral fraction alkyl silica titania catalyst and peak area under SiAOH bending at 1634 cm 1. amount of water (.,.1,.25,.54, 1., 2.5, 5. and 6.5 ml) was added dropwise into each mixture. The homogenization process was continued for 1 h after addition of water. Then the mixtures were allowed to stand in open air (humidity 6%) at room temperature for 24 h. The solid product was washed with methanol and dried under vacuum Characterizations Each solid sample was labeled as SiO 2 ATiO 2 (n,m), in which n was mol% water added into reaction mixture and m was ml toluene used as solvent. The samples were then characterized by Fourier transform infrared (FTIR) spectrometer, diffuse reflectance ultraviolet visible (DR UV Vis) spectrometer, field emission scanning electron microscope (FESEM), energy-dispersive X-ray (EDX) spectrometer, X-ray diffraction (XRD) spectrometer, N 2 adsorption surface area analyzer and transmission electron microscope (TEM). The nitrogen adsorption isotherm of samples was analyzed by using ASAP Micrometric Instrument. The samples were out gassed at 15 C under vacuum before analysis. The XRD pattern of samples was collected by a Bruker D8 advance diffractometer with wavelength of Cu K a radiation = 1.54 Å. The TEM image of samples was obtained by JEM-21. The synthesized catalysts are listed in Table 1. Study on the adsorption of adsorbed water was carried out in order to determine its role in the determination of the adsorption capacity of the alkyl silica titania samples. About 1 g of modified alkyl silica titania sample was dehydrated under vacuum at 1 C overnight. After dehydration, the sample was exposed to water vapor at room temperature, followed by the determination of the adsorbed water as a function of time. The amount of SiO 2 -TiO 2 (41,1) TiO 2 SiO 2 -TiO 2 (,) SiO 2 -TiO 2 (6) K-M / a.u SiO 2 -TiO 2 (6,) SiO 2 -TiO 2 (74,1) SiO 2 -TiO 2 (22,1) SiO 2 -TiO 2 (87,1) Wavelength /nm Wavelength /nm Fig. 3. The deconvoluted DR UV Vis spectra of the alkyl silica titania. Four selected peaks were observed at 23, 255, 285 and 315 nm.

4 26 U.K. Nizar et al. / Chemical Engineering Journal 222 (213) Tetrahedral fraction of Ti / % SiO2-TiO2(74,1) SiO2-TiO2(87,1) SiO2-TiO2(41,1) SiO2-TiO2(22,1) SiO2-TiO2(6,1) SiO2-TiO2(6,) SiO2-TiO2(,) Mol fraction of water / % Table 2 The properties of the silica titania. Entry Samples Amount of water added (mol) a 1 TiO SiO 2 ATiO 2 (,) 43 3 SiO 2 ASiO 2 (6,) 52 4 SiO 2 ATiO 2 (22,1) SiO 2 ATiO 2 (41,1) SiO 2 ATiO 2 (6,1) SiO 2 ATiO 2 (74,1) SiO 2 ATiO 2 (87,1) a b Water was added directly into the mixture of TEOT and OTS. Calculated from deconvoluted DR UV Vis peak. Tetrahedral fraction of Ti(IV) (%) b Fig. 4. The effect of addition of water towards the formation of tetrahedral Ti(IV) site. adsorbed water was determined when the amount of adsorbed water reaches its maximum Polymerization of styrene The polymerization of styrene with aqueous H 2 O 2 (3%) was carried out in 1 ml round-bottomed flask equipped with reflux condenser. The reaction mixture containing 1 mg of catalyst, 1 mmol of styrene (Merck) and 2 mmol of H 2 O 2 was placed in the flask. After stirring vigorously at 8 C for 8 h, the solid product was form. The product was washed thoroughly with methanol, and dried at 1 C in air for 1 h. The weight of products was recorded to determine the percentage of styrene conversion. 3. Results and discussion 3.1. Physical properties of alkyl silica titania catalyst Fig. 1 shows the FTIR spectra of the synthesized silica titania catalysts (see Table 1 for the labeling of samples). The broad band at 4 3 cm 1, and two bands at 1634 and 9 cm 1 are attributed to OAH stretching and OAH bending [16] of silanol group, respectively. It shows that the intensity of these peaks decreases with an increase in the amount of water added. This result suggested that the occurrence of the conversion of OAH group into OATi group to form SiAOATi bond. As the OAH stretching band at 4 3 cm 1 decreased, the present CAH stretching band at 3 28 cm 1 become increasingly clearer, suggesting the increasing of the replacement of OAH groups by OATi group and increasing the ratio of the alkyl group to hydroxyl groups on the silica titania surface. It is clearly observed in Fig. 1 that the peak area of OAH stretching at 163 cm 1 which correspond to the HAOAH deformation was decreased by an increase in the amount of water added during the synthesis of alkyl silica titania material. It is generally accepted that water adsorbed on the silica surface due to the formation of hydrogen bonding with silanol groups [17]. Thus, water adsorption should be related to the number of AOH group at the silica surface. The decrease in water adsorption might be due to the lower contain of the silanol (SiAOH group) on the silica titania surface. The decrease in peak area of the broad band at 343 cm 1, which is attributed to SiAOH stretching of surface silanols, was related to the decrease in the amount of silanol groups on the silica titania surface [18]. This suggest that the gradual decrease in the number of OAH group from SiAOH groups might be due to the formation SiAOATi bond facilitated by the addition of water. IR spectrum of SiO 2 ATiO 2 (87,1) sample show a small peak at around 97 cm 1 which is a characteristic for titanium with tetrahedral structure [19,2]. This band appears to be diminished in the other SiO 2 ATiO 2, suggesting the decrease in the amount of tetrahedral titanium in alkyl silica titania. The formation of SiAOATi bond can be rationalized by the insertion of Ti in the tetrahedral alkyl silica network. Fig. 2 shows that the relationship between the amount of tetrahedral Ti(IV) with OAH stretching band at 163 cm 1. It is worth noting that the OAH stretching band at 163 cm 1 decrease with increasing in the amount of water added during the synthesis of alkyl silica titania. To show a more evidence on the effect of water on the local coordination of Ti(IV), the analysis by DR UV Vis spectrometer was carried out. The deconvoluted DR UV Vis spectra of the catalyst (Fig. 3) were used to show the relationship between the amount of Ti(IV) site of the alkyl silica titania with the amount of water added. The deconvoluted bands at 23 and 255 nm could be assigned as the peak of isolated and distorted tetrahedral Ti(IV) site respectively, and the peaks at 285 and 315 nm were assigned as octahedral Ti(IV). As shown in Fig. 4, the amount of tetrahedral Ti(IV) was increased by the addition of water and reach maximum at SiO 2 ATiO 2 (87,1) catalyst. The preparation of silica titania without any addition of water and solvent, [SiO 2 ATiO 2 (,)] and [SiO 2 ATiO 2 (6,)], resulted in much lower tetrahedral Ti(IV) fraction suggesting that water play a key role for the formation of the tetrahedral Ti(IV) site (see Table 2). As shown in Fig. 5, it was clearly observed that the amount of adsorbed water on silica titania prepared without the addition of water [SiO 2 ATiO 2 (,)] was significantly higher than those of silica titania prepared with addition of water. The higher the amount of water added, the lower was the hydrophilicity of silica titania OH area / %T.cm SiO 2 -TiO 2 (41,1 SiO 2 -TiO 2 (6,1) SiO 2 -TiO 2 (22,1) SiO 2 -TiO 2 (74,1) SiO 2 -TiO 2 (87,1) SiO 2 -TiO 2 (6,) SiO 2 -TiO 2 (,) Adsorbed water / g Fig. 5. The amount of water adsorbed onto the surface of silica titania.

5 U.K. Nizar et al. / Chemical Engineering Journal 222 (213) Fig. 6. The EXD mapping of (a) SiO 2 ATiO 2 (,) and (b) SiO 2 ATiO 2 (87,1). obtained. FESEM micrographs of the alkyl silica titania catalysts shown in Fig. 6 represented the morphology and Ti mapping of SiO 2- ATiO 2 (,) (the lowest ratio of tetrahedral Ti(IV) octahedral Ti(IV) and SiO 2 ATiO 2 (87,1) (the highest ratio of tetrahedral Ti(IV)/octahedral Ti(IV)). It seems that the particle size of SiO 2 ATiO 2 (87,1) was smaller compared than that of SiO 2 ATiO 2 (,) and the cluster of titanium can be also recognized by X-ray mapping (EDX) (see Fig. 6). The formation of small particles of SiO 2 and the cluster of TiO 2 in SiO 2 ATiO 2 (,) sample were resulted in from self-hydrolysis and condensation of individual TEOT and OTS. However, the SiO 2 particles were distributed homogeneously on the surface for both samples, except on the location of titanium clusters. In contrast, SiO 2 ATiO 2 (87,1) catalyst showed uniform distribution of Ti and Si on the SiO 2 ATiO 2 surface (Fig. 6b). It was suggested that the presence of water facilitate the formation of SiAOATi bond and enhance the tetrahedral coordination of Ti. Based on the adsorption water experiment and Ti mapping, the models of the dispersion of TiO 2 in silica titania are proposed in Fig. 6. One proposes that the presence of the cluster of TiO 2 containing hydroxyl groups makes the silica titania prepared without addition of water [SiO 2 ATiO 2 (,)] is more hydrophilic compared to silica titania prepared by the addition of water [SiO 2 ATiO 2 (87,1)]. The XRD patterns of the silica titania samples prepared by sol gel synthesis at room temperature are shown in Fig. 7. The diffraction peaks appear in two regions namely at a small angle (2. 1 o ) and high-angle (2 23 ) 2h value. At the small angle, three peaks were recorded clearly and can be indexed using Bragg s law as (1), (111) and (22) planes, with the exception of SiO 2- ATiO 2 (,) and SiO 2 ATiO 2 (6,). The peaks of both SiO 2 ATiO 2 (,) and TiO 2 (6,) at the small angle appear with the weaker intensity. The lattice spacing (d 1 ) of all samples are in the range of nm while their lattice parameters are in the range between 2.4 and 4.5 nm. The particle size of samples is calculated by Scherrer equation vary the range of 4 35 nm. The appearance of an intense diffraction peak followed by two peaks with lower intensities as obtained at the small angle are typically 2D-hexagonal mesophase or mesostructure materials [8]. The broad diffraction peak at at 2h = 21.6 indicated the presence of amorphous silica [21,22]. The absence of the titania diffraction peaks possibly due to the very small size of titania particles or amorphous structure of titania embedded in the silica phase. One suggests that the silica titania materials have two phases namely amorphous and mesostructure phases. The mesostructure phase was formed by interconnectivity of nanocrystalline particles. The porosity of silica titania catalyst was investigated using N 2 adsorption isotherm and represented by SiO 2 ATiO 2 (,) and SiO 2- ATiO 2 (87,1). The shape of adsorption desorption isotherm and pore size distribution curve for both materials are shown in Fig. 8. The N 2 isotherm shape is identified as the type-iv [4], with a capillary condensation at the partial pressure P/Po P.35 for SiO 2 ATiO 2 (,) and P/Po P.55 for SiO 2 ATiO 2 (87,1). The surface area of SiO 2 ATiO 2 (,) and SiO 2 ATiO 2 (87,1) were 2.94 and

6 28 U.K. Nizar et al. / Chemical Engineering Journal 222 (213) (1) (a) 4 SiO 2-TiO 2(,) Intensity / a.u (111) (22) Mesostructure of SiO 2 -TiO 2 Silica phase SiO 2 -TiO 2 (87,1) SiO 2 -TiO 2 (74,1) SiO 2 -TiO 2 (6,1) Volume adsorbed (cm³/g STP) Pore Volume (cm 3 /gr) x Pore diameter (Å) Adsorption Desorption Relative pressure (P/P o) SiO 2 -TiO 2 (41,1) SiO 2 -TiO 2 (22,1) (b) SiO 2-TiO 2(87,1) θ/ o SiO 2 -TiO 2 (6,) SiO 2 -TiO 2 (,) Fig. 7. XRD pattern of series silica titania material prepared by reaction of OTS and TEOT at room temperature. Volume adsorbed (cm³/g STP) Pore Volume (cm 3 /g)x Pore diameter (Å) Adsorption 2.77 m 2 g 1, respectively. From the plot of pore size distribution curves (Fig. 9), it is confirmed that SiO 2 ATiO 2 (87,1) only possesses a well-defined pore size distribution centered around 65 Å, whereas SiO 2 ATiO 2 (,) have pore size distributions centered around 45 Å. The hysteresis loop (capillary condensation geometry) for both samples can be classified as type H3 according to IUPAC classification [23]. This type hysteresis explains that the samples are consisted slit-shape pores, non-uniform size and disordered materials as well as lamellar structure from interconnecting of particles. The type-iv isotherm shape, type-h3 hysteresis and pore sizes ranging from 45 to 65 Å indicated the SiO 2 ATiO 2 (,) and SiO 2 ATiO 2 (87,1) as mesoporous materials [23,24]. TEM image of SiO 2 ATiO 2 (,) is shown on Figs. 9 and 1. Nanoparticles located in the materials surface are titania with crystal structure FCC as determined from the SAED pattern in the inset Fig. 9a, and this finding result agreed with XRD analysis. The titania nanoparticles elongated in the direction [1] and will be broader in the direction [11]. The space between of planes (11) is about.276 nm, and their crystal orientation as seen in Fig. 9b. Meanwhile, these materials have a single shape like broom fibers arranged by lamellar structure like fibbers with diameter size about 3 5 nm (Fig. 1a. These spaces agree with the XRD analysis result. Among the lamellar structures there are spaces like pores as seen more clearly in Fig. 1b. The pore s sizes are determined by line profile as seen in Fig. 1c where the size is about nm. Fig. 1d shows schematic illustration of the lamellar structure from side and upper side point of view, where the pores located between the lamellar structures. Fig. 11a shows TEM image of the SiO 2 ATiO 2 (87,1). The lattice fringes observed at discontinue lined white square marked area, Relative pressure (P/P o) and their SAED pattern in the inset figure supported that it is come from titania crystal structure. Amorphous area more dominant than the crystal structured area. The lattice fringes have space about.759 nm as seen in Fig. 11b. As a conclusion, mesoporous silica titania materials with the mesoporous structure shaped like broom fibers arranged by lamellar structure like fibbers with diameter size about 3 5 nm has been successfully synthesized by a simple reaction between OTS and TEOT in toluene Styrene polymerization Desorption Fig. 8. The N 2 adsorption desorption isotherm curve and pore size distribution of (a) SiO 2 ATiO 2 (,) and (b) SiO 2 ATiO 2 (87,1) samples with degassing temperature of 15 C. Catalytic activity of the silica titania catalyst was investigated in polymerization of styrene in the presence of aqueous hydrogen peroxide. Fig. 12 showed the relationship between turnover number (TON) catalytic activity and fraction of tetrahedral Ti(IV) site of the prepared alkyl silica titania catalysts. It can be shown that the higher the tetrahedral fraction of Ti(IV) in the catalyst, the higher is the TON. One suggests that the presence of Ti(IV) in tetrahedral coordination enhanced the catalytic activity of the catalyst in the polymerization of styrene by using aqueous hydrogen peroxide.

7 U.K. Nizar et al. / Chemical Engineering Journal 222 (213) Fig. 9. High resolution transmission electron microscopy (HRTEM) image of SiO 2 ATiO 2 (,) materials synthesized by sol gel method at room temperature. (a) Inset is selected area electron diffraction (SAED) pattern correspond to discontinue lined white square marked area and (b) fast Fourier transform (FFT) image of the SAED patterns. Fig. 1. The image, line profile, pore sizes and structure analysis of SiO 2 ATiO 2 (,). (a) TEM image of the SiO 2 ATiO 2 (,) materials synthesized by sol gel method at room temperature. (b) TEM image enlarged from the discontinue-lined white square marked area in (a). (c) Line profile of the discontinue-white line in (b) and (d) Schematic illustration of the pore formed between the lamellar structured materials. The tetrahedral Ti(IV) is suggested to interact with H 2 O 2 before react with styrene to form OH radical. It is proposed that the reactive OH radical will be attached on the Ti(IV) active site due to the availability of the vacant coordination site on the corresponding fourfold Ti 4+ [25,26]. The Ti(IV)AOH radical bonded system will transform adsorbed styrene into radical styrene. Adsorption the next styrene molecule will release radical styrene dimer and polymerize further with other styrene molecules. On the basis of these results, a model of the heterogeneous catalysis system is proposed (see Fig. 13).

8 3 U.K. Nizar et al. / Chemical Engineering Journal 222 (213) Fig. 11. High resolution transmission electron microscopy (HRTEM) image of SiO 2 ATiO 2 (87,1) materials synthesized by sol gel method at room temperature. (a) Inset is SAED patterns correspond to discontinue lined white square marked area and (b) inverse FFT image of the SAED patterns. Turnover number SiO2-TiO2(,) TiO2 SiO2-TiO2(6,) SiO2-TiO2(74,1) SiO2-TiO2(87,1) SiO2-TiO2(6,1) SiO2-TiO2(41,1) SiO2-TiO2(22,1) orthotitanate (TEOT) in toluene. The formation of tetrahedral Ti(IV) can be controlled by the addition of water to the reaction mixture. This synthesis methodology is advantageous because of its simplicity. The presence of tetrahedral Ti(IV) in alkyl silica titania gave the beneficial effect on catalytic activity of the catalyst in styrene polymerization. The silica titania materials with the mesoporous structure shaped like broom fibers arranged by lamellar structure like fibbers with diameter size about 3 5 nm has been successfully synthesized by a simple reaction between OTS and TEOT in toluene Tetrahedral fraction of Ti / % Fig. 12. The relationship between tetrahedral fractions of Ti(IV) site and turnover number in styrene polymerization by using aqueous hydrogen peroxide. OH Ti HC CH 2 Acknowledgements We gratefully acknowledge the funding from The Ministry of Higher Education (MOHE) Malaysia, under Fundamental Research Grant Scheme, and Universiti Teknologi Malaysia (UTM), under Research University Grant. U.K.N. thanks Directorate General of Higher Education, the Ministry of Education and Culture, Indonesia and West Sumatera Province Office, Indonesia for financial support. References 1/2 H 2 O 2 Ti 4. Conclusions The role of water in formation of alkyl silica titania catalysts has been investigated by the addition different amount of water to the mixture of octadecyltrichlorosilane (OTS) and tetraethyl HO Ti HC H 2 C CH 2 CH C H H 2 C n Polystyrene Fig. 13. The proposed mechanism of styrene polymerization over alkyl silica titania catayst. [1] J. Zhu, J. Xie, M. Chen, D. Jiang, D. Wu, Low temperature synthesis of anatase rare earth doped titania silica photocatalyst and its photocatalytic activity under solar-light, Colloid Surf. A 355 (21) [2] C. Akly, P.A. Chadik, D.W. Mazyck, Photocatalysis of gas-phase toluene using silica titania composites: performance of a novel catalyst immobilization technique suitable for large-scale applications, Appl. Catal. B 99 (21) [3] J.L. Coutts, L.H. Levine, J.R. Richards, The effect of photon source on heterogeneous photocatalytic oxidation of ethanol by a silica titania composite, J. Photochem. Photobiol. A 225 (211) [4] M. Brigante, P.Z. Schuls, Remotion of the antibiotic tetracycline by titania and titania silica composed materials, J. Hazard. Mater. 192 (211) [5] J. Ren, Z. Li, S. Liu, Y. Xing, K. Xie, Silica titania mixed oxides: SiAOATi connectivity, coordination of titanium, and surface acidic properties, Catal. Lett. 124 (28) [6] G. Li, N.M. Dimitrijevic, L. Chen, J.M. Nichols, T. Rajh, K.A. Gray, The important role of tetrahedral Ti 4+ sites in the phase transformation and photocatalytic activity of TiO 2 nanocomposites, J. Am. Chem. Soc. 13 (28) [7] H. Nur, Modification of titanium surface species of titania by attachment of silica nanoparticles, Mater. Sci. Eng. B 133 (26) [8] O.K. Kholdeeva, N.N. Trukhan, Mesoporous titanium silicates as catalysts for the liquid-phase selective oxidation of organic compounds, Russ. Chem. Rev. 75 (5) (26) [9] M.J. Fraile, I.J. Garcia, A.J. Mayoral, E. Vispe, Effect of the reaction conditions on the epoxidation of alkenes with hydrogen peroxide catalyzed by silicasupported titanium derivatives, J. Catal. 24 (21) [1] M.J. Fraile, I.J. Garcia, A.J. Mayoral, E. Vispe, Silica-supported titanium derivatives as catalysts for the epoxidation of alkenes with hydrogen peroxide: a new way to tunable catalytic activity through ligand exchange, J. Catal. 189 (2) [11] W. Que, Z. Sun, Y.L. Lam, Y.C. Chan, C.H. Kam, Effects of titanium content on properties of sol gel silica titania films via organically modified silane precursors, J. Phys. D. 34 (21)

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