Simple sol–gel process to obtain silica-coated anatase particles with enhanced TiO2-SiO2 interfacial area

Effect of Calcination Temperature of SiO2/TiO2 Photocatalysts on UV-VIS and VIS Removal Efficiency of Color Contaminants

This paper presents the effect of fumed silica modification and calcination temperature on the physicochemical properties of photocatalysts and their activity under the UV-VIS and VIS light range. The materials were obtained by hydrolysis of titanium tetraisopropoxide (TTIP) combined with a calcination step. The obtained nanomaterials were characterized using analytical methods such as X-ray diffraction XRD, FT-IR/DRS infrared spectroscopy, UV-Vis/DRS spectroscopy and SEM scanning electron microscopy. BET specific surface area and zeta potential were also measured. It was observed that SiO2 modification inhibited the transformation phase of anatase to rutile and the increase in crystallite size during calcination. The calcination process contributed to a change in the surface character of photocatalysts under study from positively to negatively charged. The photocatalytic activity of samples was identified by determining the methylene blue decomposition under UV-VIS and VIS light. Experimental results showed that the addition of SiO2 and the calcination process increased the photoactivity. The obtained materials showed higher activity compared to the reference samples. It was found that the degree of dye removal increased along with increased calcination temperature. The highest activity was observed for photocatalyst SiO2(11.1%)/TiO2_600.

Hydrolytic Modification of SiO2 Microspheres with Na2SiO3 and the Performance of Supported Nano-TiO2 Composite Photocatalyst

Modified microspheres (SiO₂-M) were obtained by the hydrolytic modification of silicon dioxide (SiO₂) microspheres with Na₂SiO₃, and then, SiO₂-M was used as a carrier to prepare a composite photocatalyst (SiO₂-M/TiO₂) using the sol-gel method; i.e., nano-TiO₂ was loaded on the surface of SiO₂-M. The structure, morphology, and photocatalytic properties of SiO₂-M/TiO₂ were investigated. Besides, the mechanism of the effect of SiO₂-M was also explored. The results show that the hydrolytic modification of Na₂SiO₃ coated the surface of SiO₂ microspheres with an amorphous SiO₂ shell layer and increased the quantity of hydroxyl groups. The photocatalytic performance of the composite photocatalyst was slightly better than that of pure nano-TiO₂ and significantly better than that of the composite photocatalyst supported by unmodified SiO₂. Thus, increasing the loading capacity of nano-TiO₂, improving the dispersion of TiO_2, and increasing the active surface sites are essential factors for improving the functional efficiency of nano-TiO₂. This work provides a new concept for the design of composite photocatalysts by optimizing the performance of the carrier.

Enhancement of Photocatalytic Oxidation of Glucose to Value-Added Chemicals on TiO2 Photocatalysts by A Zeolite (Type Y) Support and Metal Loading

TiO2-based photocatalysts synthesized by the microwave-assisted sol-gel method was tested in the photocatalytic glucose conversion. Modifications of TiO2 with type-Y zeolite (ZeY) and metals (Ag, Cu, and Ag-Cu) were developed for increasing the dispersion of TiO2 nanoparticles and increasing the photocatalytic activity. Effects of the TiO2 dosage to zeolite ratio (i.e., TiO2/ZeY of 10, 20, 40, and 50 mol %) and the silica to alumina ratio in ZeY (i.e., SiO2:Al2O3 of 10, 100, and 500) were firstly studied. It was found that the specific surface area of TiO2/ZeY was 400–590 m2g−1, which was higher than that of pristine TiO2 (34.38 m2g−1). The good properties of 20%TiO2/ZeY photocatalyst, including smaller particles (13.27 nm) and high surface area, could achieve the highest photocatalytic glucose conversion (75%). Yields of gluconic acid, arabinose, xylitol, and formic acid obtained from 20%TiO2/ZeY were 9%, 26%, 4%, and 35%, respectively. For the effect of the silica to alumina ratio, the highest glucose conversion was obtained from SiO2:Al2O3 ratio of 100. Interestingly, it was found that the SiO2:Al2O3 ratio affected the selectivity of carboxylic products (gluconic acid and formic acid). At a low ratio of silica to alumina (SiO2:Al2O3 = 10), higher selectivity of the carboxylic products (gluconic acid = 29% and formic acid = 32%) was obtained (compared with other higher ratios). TiO2/ZeY was further loaded by metals using the microwave-assisted incipient wetness impregnation technique. The highest glucose conversion of 96.9 % was obtained from 1 wt. % Ag-TiO2 (40%)/ZeY. Furthermore, the bimetallic Ag-Cu-loaded TiO2/ZeY presented the highest xylitol yield of 12.93%.

SiO2@TiO2 Composite Synthesis and Its Hydrophobic Applications: A Review

Titanium dioxide is well known for its photocatalytic properties and low toxicity, meanwhile, silicone dioxide exhibits hydrophobic and hydrophilic properties and thermal stability. The union of these two materials offers a composite material with a wide range of applications that relate directly to the combined properties. The SiO2-TiO2 composite has been synthesized through physical methods and chemical methods and, with adequate conditions, morphology, crystallinity, boundaries between SiO2-TiO2, among other properties, can be controlled. Thus, the applications of this composite are wide for surface applications, being primarily used as powder or coating. However, the available research information on this kind of composite material is still novel, therefore research in this field is still needed in order to clarify all the physical and chemical properties of the material. This review aims to encompass the available methods of synthesis of SiO2-TiO2 composite with modifiers or dopants, the application and known chemical and physical properties in surfaces such as glass, mortar and textile, including aspects for the development of this material.

Study of the structure and characteristics of mesoporous TiO2 photocatalyst, and evaluation of its factors on gaseous formaldehyde removal by the analysis of ANOVA and S/N ratio

This study differs from previous studies of TiO2/SiO2 in that 0.5-10 μm microsized TiO2-rutile based catalysts (TR catalysts) with varying proportions of titanium and silicon were synthesized using a one-step modified hydrothermal method. At Ti/Si = 1/9, a two-dimensional channel-structured catalyst with a morphology resembling that of SBA-15 was obtained. In contrast, at Ti/Si = 3/7 or 5/5, a three-dimensional porous structure was formed, and Ti-O-Si-C bonds appeared. The structure of the TR catalyst transformed due to the decrease in C-Si bond content and the increase in C-C bond content with increasing Ti/Si ratio. The results indicated that the rutile phase was the main crystal phase of the TR catalyst. The small crystal size and large rutile phase content of the mesoporous TR catalyst contributed to the low band gap energy below 3.0 eV. Under 2 × 10 W lamp irradiation with either UVA or visible light, the three TR catalysts showed better formaldehyde (HCHO) removal efficiency than P25. Furthermore, the Taguchi method was employed to evaluate the catalytic factors by analysis of variance (ANOVA) and S/N ratio. The results revealed the contributions of each of the three factors to HCHO removal efficiency over TR catalysts to be as follows: space velocity (62%), Ti ratio (32%), and time on stream (5%). The TR catalyst with Ti/Si = 1/9 showed good HCHO removal efficiency with a high S BET (787.1 m2 g-1) and large pore volume (0.95 cm3 g-1) for a residence time of over 2.29 × 10-1 s under visible light irradiation. Microwave-assisted EG reduction was successfully applied to dope a TR catalyst with nanosized Pt particles in a short synthesis time. After Pt doping, the removal efficiency in the stream improved and stabilized. The Pt particles were Pt0 and proved effective for improving the photocatalytic removal of HCHO over the TR catalyst by prolonging the separation time of the electron-hole pairs. Overall, the Pt/TR catalyst is a potential material for pollutant removal and can be easily separated from the pollutant removal system since the catalysts are microsized.