Titania-silica Composites Research Articles

Sintesis Komposit Titatnia-Silika dengan Proses Sol Gel

Sintesis komposit titania silika telah berhasil dibuat dari geothermal sludge dengan menggunakan metode sol gel dan sonikasi. Sonikasi digunakan untuk mengecilkan partikel TiO2 dengan bantuan alat sonikator dengan larutan asam sulfat sebagai pelarut TiO2. Sedangkan metode sol gel digunakan untuk mengkompositkan antara silika dari geothermal sludge yang diektraksi menggunakan NaOH menjadi larutan natrium silika dengan larutan TiO­2 yang sudah disonikasi sehingga tebentuk komposit titania silika. Untuk mempelajari pengaruh komposisi dari komposit digunakan TiO2 dengam berat 4-8 gram dan pH gelling dari proses sol gel dengan pH 4-8. Komposit titania silika yang tebentuk akan dikarakterisasi menggunakan X-Ray fluorescence (XRF), X-Ray Diffraction (XRD), dan Spektroskopi Fourier Transform Infrared (FTIR). Dari analisa yang dilakukan didapatkan hasil bahwa, dengan penambahan berat TiO2 yang berbeda dan pH gelling yang berbeda didaptkan rasio silika/titania dengan rentang 0,3113-1,5268.Gugus yang menunjukkan adanya ikatan titania silika dapat dilihat pada bilangan gelombang 965,1 dan 967,03 cm-1. Pola XRD dari komposit menunjukkan adanya silika amorf dan kristal titania sehingga terdapat titania dan silika dalam produk. Komposit titania silika dapat digunakan pada proses adsorpsi jika komposisi silika lebih banyak dibanding titania, sedangkan jika komposisi titania lebih banyak digunakan pada proses oksidasi.

Simultaneous photooxidation and photoreduction of phenol and Cr(VI) ions using titania modified with nanosilica

Abstract The photocatalytic process of phenol oxidation and Cr(VI) reduction in the presence of nano-silica modified titania was carried out. The activity of composites was tested using two different light sources. The photocatalysts with 10% of nanosilica showed the highest activity. The calcination temperature (200–800 oC) significantly determined the sensitivity of the obtained materials to the light source used. Photocatalysts alternately adsorbed and desorbed Cr(VI) ions from the reaction mixture during irradiation. In the one-component mixture, complete oxidation of phenol was observed using material calcined at 650 oC, after 3 h of UV-VIS irradiation. In the reaction mixture of Cr(VI) and phenol, the highest activity was demonstrated by photocatalyst calcined at 300 oC. The concentration of phenol decreased in proportion to the decrease of chromium ions. The obtained titania-silica composites showed oxidizing properties towards phenol and reductive properties toward Cr(VI) ions.

Fiber optic pH sensor using TiO2-SiO2 composite layer with a temperature cross-sensitivity feature

An intensity-modulated fiber optic pH sensor is fabricated and demonstrated in the present work. Three pH indicators, bromothymol blue, cresol red and chlorophenol red along with titania-silica composite are used as pH sensitive layers. The sensing principle is based on evanescent field absorption and then transmitted power loss of light guided within the fiber. The sensor parameters were studied by changing the volume ratio of the composite layer, and a maximum sensitivity of 1.76 μW/pH is obtained for 1:3 (TiO2:SiO2) composite layer with excellent linear response for pH value from 2 to 11. The TiO2 content induces strong interaction between guided light and outer medium and the concentration of SiO2 was increased to improve porosity in the sol-gel matrix to achieve enhanced sensitivity. A straight forward way has been introduced to utilize the temperature cross-sensitivity feature of the optical fiber pH sensor with high temperature sensitivity. In addition to its high sensitivity, the proposed sensor has additional characteristics of fast time response and good stability which are very useful in biomedical, environmental, food processing and industrial applications.

Influence of synthesis conditions on the properties of photocatalytic titania-silica composites

Titania-silica composites are a promising alternative to titania for photocatalysis, because of their lower material costs, longer lifetimes and higher activities. Different synthesis routes for titania-silica composites were thoroughly investigated in this study to gain more fundamental insight on their impact on the resulting samples and their photocatalytic oxidation efficiency. The investigated routes were based on precipitation, slow addition of an alkoxide precursor and sol-gel method. The silica for the composites was synthesized by dissolving the silicate mineral olivine in sulfuric acid. This method is cheaper, environmentally friendly and produces silica with favorable properties (i.e. large surface area with a high hydroxyl density) to support the titania. The resulting samples were tested by measuring their efficiency to oxidize nitric oxide under UV-light irradiation, XRD, nitrogen physisorption, FTIR and XPS. The results show that the most active photocatalysts were prepared by precipitation by slow addition of water or slow addition of precursor to a low water content dispersion. In addition, an optimal pH of 3 was observed for these synthesis methods. Compared to pure titania, the prepared titania-silica composites with only 15% titania showed slightly higher photocatalytic activities (82.3% vs. 78.9%), showing the composites to be a promising cost-effective alternative to the current photocatalysts.

Thermal and calorimetric investigations of titania–silica composites

The paper presents the studies of effects of TiO2 amount differentiation on the structural and thermal properties of titania–silica complex oxides prepared by chemical vapor deposition of TiCL4 onto the Si-40, Si-60, and Si-100 silica gels. The mesoporous materials, characterized by a varied pore structure with highly developed surface and large pore volume, were obtained. The porous structure of materials under investigations was characterized by the low-temperature nitrogen adsorption–desorption method as well as by power spectral density calculated from the calorimetric investigations of water confined in the pores. Moreover, the thermodesorption of water using the quasi-isothermal thermogravimetry was used to characterize their thermal and surface properties. The adsorbed water layers and the concentration of weakly and strongly bound water as well as the surface free energy on the adsorbent–water interfaces were calculated. It was stated that the increase of titania content causes a gradual decrease of specific surface area and has a significant effect on the porous structure formation. The water thermodesorption from the surface proceeds in few stages because of the porosity created by TiO2. The decrease in the total surface free energy (Δ GΣ) can be observed with the increasing TiO2 content. The largest Δ GΣ value at the adsorbent/strongly bound water interface is exhibited by the adsorbents of Si-100 series. The lowering of the freezing/melting points of water contained in the pores of the studied materials is strongly connected with their porous structure.

Size controlled nanocrystalline TiO<SUB align="right">2 supported on mesostructured SBA-15 for better photocatalytic performance

Nanocrystalline TiO2 was prepared using sol gel hydrolysis and silica SBA-15 using organic solvent method. The synthesised SBA-15 served as the TiO2 support to reduce the TiO2 grain size and well-dispersed TiO2 for enhancement of photocatalytic activity. The synthesised titania/silica composites were characterised by X-ray diffraction, FTIR, TEM, UV-Visible spectroscopy, etc. TEM micrographs showed that the organic solute template method could prepare the titania-silica composite, and successfully embedded titania in SBA-15 channel. The mesoporous structure restrained the titania grain size within 5–7 nm which caused blue shift identified by UV-Vis spectra. The photo catalytic test of this material has been studied using methylene blue which shows improved performance than TiO2. Titania loading on the silica matrix decreases the surface area of the support and there is systematic decrease in their pore volume values, as titania content increases.

Synthesis and Characterization of Titania-Rice Husk Silica Composites as Photocatalyst

This article describes the synthesis of titania-silica composites by a sol-gel method using a mixture of silica of rice husk and titanium butoxide sols. Microstructures were examined at calcination temperature in the range of 500 to 700 °C, with temperatures interval of 50 °C. The sintered catalysts were subsequently tested for photodegradation of methylene blue (MB) under ultraviolet and sunlight rays. Physical characteristics were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM)/energy dispersive X-ray spectroscopy (EDS), and Brunauer-Emmett-Teller (BET). The XRD results did not show the presence of silica crystal phase in each sample. The results showed that the highest BET surface area of samples was obtained at the temperature of 650 °C. In sample calcined 500 °C, the activity of the catalyst on MB was relatively similar in both sunlight and ultraviolet rays.

Esterification of oleic acid by heteropolyacid/TiO2SiO2 catalysts synthesized from less expensive precursors

AbstractA series of 12‐tungstophosphoric acid [HPW, H3PW12O40 (HPW)] catalysts supported on mesoporous titania–silica composite (TSC) were prepared by impregnation method. Primarily, TSC with mesostructure was successfully prepared by a modified sol–gel process using a less expensive silica precursor (sodium silicate) and titanium oxychloride as a titania source. In order to develop catalysts with various properties, the HPW loading over mesoporous TSC was controlled between 5 and 50 wt%. The surface morphology and structural properties of the prepared catalysts were characterized using N2 gas physisorption analysis, Fourier transform infrared spectroscopy, X‐ray diffraction, ultraviolet spectroscopy, transmission electron microscopy, and scanning electron microscopy analysis. The X‐ray diffraction and ultraviolet spectroscopy results were useful in determining the HPW dispersion on the support material. The catalytic activities of the samples were tested in liquid phase esterification of oleic acid with methanol. The results suggested that HPW dispersion on the support material was essential for the stability and performance of the catalysts during the esterification reaction. Even though the activity of the synthesized catalysts increased with increasing HPW loading, the homogeneity decreased in the samples with higher HPW content (30–50 wt%). The 20%HPW/TSC sample was found to be an active and catalytically stable catalyst, which was successfully regenerated and recycled for three consecutive runs. Copyright © 2015 Curtin University of Technology and John Wiley & Sons, Ltd.

Titania-Silica Composites: A Review on the Photocatalytic Activity and Synthesis Methods

The photocatalyic activity of titania is a very promising mechanism that has many possible applications like purification of air and water [1]-[4]. To make it even more attractive, titania can be combined with silica to increase the photocatalytic efficiency and durability of the photocatalytic material, while lowering the production costs [1]. In this article, relevant literature is reviewed to obtain an overview about the chemistry and physics behind some of the different parameters that lead to cost-effective photocatalytic titania-silica composites. The first part of this review deals with the mechanisms involved in the photocatalytic activity, then the chemistry behind certain methods for the synthesis of the titania-silica composites is discussed, and in the last and third part of this review, the influence of silica supports on titania is discussed. These three sections represent three different fields of research that are combined in this review to obtain better insights on the photocatalytic titania-silica composites. While many research subjects in these fields have been well known for some time now, some subjects are only more recently resolved and some subjects are still under discussion (e.g. the cause for the increased hydrophilic surface of titania after illumination). This article aims to review the most important literature to give an overview of the current situation of the fundamentals of photocatalysis and synthesis of the cost-effective photocatalyic composites. It is found that the most cost-effective photocatalytic titania-silica composites are the ones that have a thin anatase layer coated on silica with a large specific surface area, and are prepared with the precipitation or sol-gel methods.

Biodiesel production by sulfated mesoporous titania–silica catalysts synthesized by the sol–gel process from less expensive precursors

A sulfated titania–silica composite (S-TSC) was obtained through surface modification of mesoporous titania–silica composite synthesized using less expensive precursors; titanium oxychloride and sodium silicate as titania and silica sources respectively. A pre-formed titania sol facilitated the synthesis of a mesoporous composite with a high BET surface area (520m2/g), suitable for surface modification using sulfuric acid to improve its catalytic performance. The materials synthesized via this process were examined by XRD, XRF, FTIR, SEM, TEM, TGA, and N2 physisorption studies. FTIR analysis showed the vibration band of the TiOSi bond at 943cm−1, suggesting the incorporation of titania into silica to form a composite. This vibration band was substantially shifted to 952cm−1 after the attachment of the sulfate group. The catalytic activity of a series of as-prepared TSC, S-TSC calcined samples and pure H2SO4 were evaluated for esterification of oleic acid and transesterification of waste oil with methanol to yield methyl esters. It was observed that at these reaction conditions, S-TSC-450 and S-TSC-550 possessed high catalytic activity comparable to that of pure H2SO4 implying that surface modification of the titania–silica composite improves its acidic properties.

Influence of titania content on the mesostructure of titania–silica composites and their photocatalytic activity

Abstract \Titania–silica composites (TSC) with various Ti/Si ratios were synthesized via sol–gel process using less expensive precursors; sodium silicate solution as a silica source and titanium oxychloride as a titania source. The influence of varying Ti content in the composites was examined by FTIR, SEM, TEM, DTA/TGA, N2 physisorption studies, XRF and XRD. The BET surface area of the raw materials increased with increasing Ti/Si ratio up to 2.9 (461 m2/g) but further increase of Ti content beyond that ratio yielded composites with decreased surface area. The effect of aging evaluated in the sample with Ti/Si = 2.9 revealed that aging the composite for 2 h yields titania–silica powder with the highest surface area (461 m2/g). The FTIR analysis displayed the presence of a vibration band at 945 cm− 1, assignable to hetero linkage of the Si–O–Ti depicting the incorporation of TiO2 into SiO2 to form a composite. Moreover, photodegradation of methyl orange (MO) by the samples calcined at 800 °C showed that the TSC-5-800 (Ti/Si = 5.6) exhibited the highest maximum photocatalytic activity of all the composites.

Magnetic titania-silica composite–Polypyrrole core–shell spheres and their high sensitivity toward hydrogen peroxide as electrochemical sensor

A novel core–shell sphere with controlled shell thickness was synthesized by in situ chemical oxidative polymerization of pyrrole on FTS (Fe2O3/TiO2/SiO2 composite) surface. The dual porosity of 2–3nm and 40–50nm in FTS core particle provides the hybrids with a high surface area to volume ratio, which enormously facilitates the molecule diffusion process. Furthermore, the porous FTS particle encapsulate Fe2O3 and TiO2 leading to its synergetic interaction with the PPy coating based on FTIR analysis. The unique structure and composition of the hybrid spheres result in new sensing property that is not available from their single counterparts. Cyclic voltammetry results demonstrate that the spheres with appropriate concentration of PPy exhibit enhanced electrocatalytic activity toward the reduction of H2O2 in 0.1M phosphate buffer solution. The sensing performance tests show that the hybrids possess good linear response in wide H2O2 concentration range (10–4000μM) and high sensitivity to H2O2 (0.653AM−1cm−2) at room temperature. The formation mechanism of the spheres was proposed based on the fact that the FTS core was coated firstly by a smooth PPy layer and then PPy nanoparticles. The work reported here provides an alternative concept for preparation of functional materials with new nanostructures and properties.

Peptization technique in the synthesis of titania–silica composites and their photocatalytic properties

A comparative study of titania–silica composite (TSC) synthesized via peptization sol–gel method was conducted. Typically, titanium hydroxide gel (Ti(OH)4) was formed by condensation of titanium oxychloride solution using adequate amount of ammonium hydroxide solution. The preformed gel was peptized either in silicic acid (SA) or nitric acid (NA) to form a sol. The composite was characterized by XRD, FTIR, SEM, TEM, TGA, and N2 physisorption studies. The XRD patterns and the TEM micrographs confirmed that thermal-derived samples of the composite, formed using silicic acid as a silica source and peptizing agent (TSC–SA), yielded TiO2SiO2 composite with a single-phase (anatase phase); while a mixture of both anatase and rutile phases were observed in the composite (TSC–NA), where nitric acid was used as a peptizing agent. FTIR analysis showed the vibration band assignable to the TiOSi bond at 945cm−1, suggesting that titania was incorporated into silica to form a composite. Furthermore, a simple experiment of photodegradation of methyl orange in the presence of sunlight was performed to demonstrate the practical efficacy of the composites synthesized via this method. The results indicated that the calcined samples of TSC–NA-800 had the highest activity due to its superior properties.

Manufacture of Titania-silica Composites by Sol-gel Method as an Anode Material

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Two step synthesis of a mesoporous titania–silica composite from titanium oxychloride and sodium silicate

Mesoporous titania–silica composite (MTSC) with a large surface area (387m2/g) and large pore volume was synthesized by a two step condensation sol–gel method. Transparent TiO2 sol was formed at room temperature through condensation and peptization of titanium oxychloride solution using ammonium hydroxide and aqueous nitric acid respectively. Sodium silicate was used as a silica source to form a composite with the preformed TiO2 sol. The physical properties of the composite were examined by Fourier Transform infrared (FTIR), BET surface area, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The nitrogen physisorption behavior of the synthesized composite was compared to that obtained from grafting and one-pot co-condensation methods using the same precursors in the presence of cetyltrimethylammonium bromide (CTAB). It was found that MTSC synthesized under this method possessed large pore sizes and pore volume but its thermal stability was comparatively low. FTIR spectra showed the formation of a TiOSi bond at 940cm−1 suggesting that titania was incorporated in silica to form a composite. The XRD patterns showed that the major phase of the titania had an anatase phase up to 900°C but it transforms into rutile when calcined at 1000°C. Furthermore the EDS studies of the as-synthesized and calcined samples substantiated the formation of titania–silica composites.

Titania-Silica Nanocomposite Photocatalysts with Application in Stone Self-Cleaning

Mesoporous titania-silica composites that have photocatalytic activity have been synthesized by mixing ethoxysilane oligomers and titanium dioxide nanoparticles in the presence of a nonionic surfac...

Mesoporous titania–silica composite from sodium silicate and titanium oxychloride. Part I: grafting method

In this study, we report a versatile method for designing a titania–silica composite using relatively inexpensive precursors. The composite was synthesized by grafting (impregnating) a precursor of a guest component into the preformed host’s solid network. The latter was prepared using sodium silicate as a silica precursor in the presence of cetyltrimethylammonium bromide (CTAB). A freshly prepared solution of titanium oxychloride (TiOCl2, titania precursor that is relatively stable) was introduced into the host’s network to develop a titania–silica composite with initial ratio of Ti:Si = 1. The final product has the overall ratio of Ti:Si = 7:3 and was obtained after calcination for 5 h at 600–1000 °C. The XRD patterns for the calcined samples indicate the presence of TiO2, and there was a significant increase in peak intensity as the calcination temperature increased. EDS, XRF, and FT-IR analyses indicated the formation of a highly pure composite rich in Ti, Si, and O. A Si–O–Ti band at 954 cm−1 was observed, confirming the formation of a titania–silica composite. A composite with optimum properties (homogenous dispersion of the composite and less individual oxide phase separation) was obtained at 600 °C. A similar experiment was also conducted in the absence of CTAB. In this case, the final product was microporous, rendering it unsuitable for some applications.

Titania–silica composites with less aggregated particles

Less aggregated titania–silica composite was developed by a versatile and reproducible method using relatively cheap precursors. The final product has more suitable properties than the conventional materials. The composite was synthesized by using sodium silicate, as a silica precursor, and freshly prepared TiOCl 2 as a titania source. The final product was obtained after subsequent calcination for 5 h at 300 to 1000 °C. The primary particles of the composite, as examined by SEM technique, are generally less aggregated. The XRD patterns for the calcined samples indicate the presence of TiO 2 and there is a significant increase of peak intensity as the calcination temperature increases. EDS and XPS analyses confirmed the formation of pure composite rich in Ti, Si, and O. Nitrogen physisorption studies reveal that the composite is mesoporous and have large BET surface area (~ 375 m 2/g). A simple experiment of photoreduction of methyl orange under solar radiation was attempted to demonstrate the reliability and improvement of titania–silica composite in practice. It was found out that its efficiency is high as compared to P-25 TiO 2 under solar light. The results demonstrate that composite with desirable properties for various applications can be obtained via the present route.

Effect of PEG with different M W as template direction reagent on preparation of porous TiO2/SiO2 with assistance of supercritical CO2

Titania–silica composite have been prepared using polyethylene glycol (PEG) with different molecular weights (M w), PEG20000, PEG10000, and PEG2000, as template in supercritical carbon dioxide (SC CO2). The composite precursors were dissolved in SC CO2 and impregnated into PEG templates using SC CO2 as swelling agent and carrier. After removing the template by calcination at suitable temperature, the titania–silica composite were obtained. The composite were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, and nitrogen sorption–desorption experiment. Photocatalytic activity of the samples has been investigated by photodegradation of methyl orange. Results indicate that there are many Si–O–Ti linkages in the TiO2/SiO2 composite; the PEG template has a significant influence on the structure of TiO2/SiO2. In addition, the TiO2/SiO2 prepared with PEG10000 exhibited high photocatalytic efficiency. So this work supplies a clue to control and obtain the TiO2/SiO2 composite with different photocatalytic reactivity with the aid of suitable PEG template in supercritical CO2.

Porous TiO 2/SiO 2 composite prepared using PEG as template direction reagent with assistance of supercritical CO 2

Titania–silica mesoporous composites have been prepared using polyethylene glycol (PEG) 20,000 as a template direction reagent with the assistance of supercritical carbon dioxide (SC CO 2). For this preparation method, the composite precursors of tetrabutyl titanate (TBTT) and tetraethyl orthosilicate (TEOS) were dissolved in supercritical CO 2 and impregnated into PEG 20,000 using SC CO 2 as swelling agent and carrier. After removal of the PEG template by calcination in air at suitable temperatures, porous titania–silica composites were obtained. Effects of CO 2 pressure and temperature have been studied on the impregnation ratio during the supercritical fluid condition. The composite products were characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), FTIR spectroscopy, nitrogen sorption–desorption experiments, scanning electronic microscope (SEM), and transmission electron microscope (TEM). XRD and nitrogen sorption–desorption experimental results indicate that the titania–silica composite crystallized in anatase phase and has a preferable BET surface area up to 301.98 m 2/g. It was also demonstrated that the microstructure and macroproperty of TiO 2/SiO 2 composites depend strongly on the experimental pressure during the impregnation process in SC CO 2. At suitable CO 2 pressure, silica even can be found in a single crystalline structure in nature by observation of TEM. At the same time, SEM indicates that the composite product existed in a spheric form or a cubic form inserted with many holes. So this work provides a new route to control and obtain the special micrography of TiO 2/SiO 2 composites with the aid of suitable polymer templates in supercritical CO 2.