Preparation And Characterization Of TiO₂ Supported On Mesopopous Silica Molecular Sieve

Titanium dioxide is well known as a cheap, nontoxic, chemical stability, large-band gap (Eg≥3.2eV)semiconductor with photocatalytic activity. It has a large number of applications such as in environmental purification, decomposition of organic contaminants, utilization of solar energy, synthesis of chemistry, etc. especially there has been substantial interest in photocatalys. However, their effective applications are hinder by two serious disadvantages. Firstly, small particles trend to agglomerate into large particles, making against on catalyst performance. Secondly, the separation and recovery of catalyst is difficult. For those reasons many researchers have been focused on mesoporous materials supporting titania catalysts In this thesis, we have investigated the synthesis of TiO₂/MCM-41 and TiO₂/SBA-15 materials by a post-synthesis step via Ti-alkoxide hydrolysis. The synthesized materials were characterized by powder X-ray diffraction, nitrogen adsorption-desorption, Fourier transform infrared spectroscopy, and state diffuse UV-visible spectroscopy. Photocatalytic activity of the samples has been tested use methylene blue(MB) as the model pollutant.We have investigated the synthesis of TiO₂/MCM-41 materials by a post-synthesis step via titanium isopropoxide(TTIP) hyrolysis. The synthesized catalysts have a relatively high thermal stability. The addition of mesoporous MCM-41 prevents the anatase to futile phase transformation and the growth of crystal grain. The analyzing results showed that besides the adsorption ability of TiO₂ crystal, other factors, such as crystal phase, surface area, crystallite size, and crystallinity et al, also olay an important role in influencing photoactivity. Furthermore there is an optimal ratio of Ti: Si, too high or too low both leading to decrease the photocatalytic activity. Catalyst 50% TiO₂/MCM-41-800℃has the highest rate constant of 0.0438rain^-1, which is much higher than that of P-25(0.0129 min^-1).The samples of TiO₂/SBA-15 were prepared by the sol-gel process using two different precursors: titanium ethoxide(TEOT) and titanium isopropoxide(TTIP). The titanium alkoxides dissolved in various alcohols(methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 1-hexanol). The results showed that the crystallite size, the pore size and crystallinity have been influenced by alcohols. In general, a increase in the crystallite size and pore size with increase in the number of carbon atoms in the alcohols.