Synthesis, Characterization Of Nanosize TiO₂ Composite And Its Application For Photocatalytic Degradation Of Biorefractory Organic Compounds

Photocatalytic reactions of semiconductors have received special attention in the decomposition of hazardous organic compounds because of their complete mineralization ability and possible application to pollution control using solar energy. The conflict of fixation and photoactivity of photocatalyst is one of the main problems restraining the practical application of photocatalytic technology. In this paper, the active nanoscale TiO: pillared bentonite composite photocatalyst was synthesized and characterized. The effects of preparing conditions such as calcination temperature, Ti/bentonite and initial pH on the physical characterization and the photoactivity were investigated. Moreover, the photodegradation of cationic red GTL (GTL), cationic blue X-GRL (X-GRL) and polyvinyl alcohol (PVA) were also discussed in detail.In the third chapter, titanium dioxide pillared bentonite nanocomposite prepared by acid-catalyzed sol method was characterized, and was as photocatalyst in the degradation of cationic azo dyes and PVA in water. The 26 angle of the (001) reflection corresponding to the basal spacing of the clays was 5.88 ?for the bentonite, 5.60?for the 323 K treated sample, and 9.06D for the 773 K treated sample. These corresponded to dOOl basal spacings of 1.502 nm, 1.577 nm and 0.982 nm for the bentonite, 323 K treated sample, and 773 K treated sample, respectively. It could be seen that the dOOl basal spacing had been increased from 1.502 to 1.577 nm after being treated at 323 K by this process. This result demonstrated the insertion of species by TiOa sol particulates with positive charges exchange reaction with the inorganic cations such as Na+ and Ca2+ in the galleries of bentonite because that the TiC>2 sol particulate species were much larger than the inorganic cations. The reduction in interlayer distance with an increase in the calcination temperature indicated the dehydration of TiC>2 sol particulate species and the formation of titanium dioxide. The final inserted TiCh was also proved by X-ray photoelectron spectrometer (XPS). The insertion of TiOi had influenced the site of Si4+ in the structure of bentonite as probed by infrared spectra (IR) and XPS. The onset corresponding to guest TiOi slightly blue shifted, and it might be due to the size quantization effect. The photocatalytic activities of those nanocompositephotocatalysts were much higher than those of the pure titanium dioxides and TiOi supported on diatomite. In addition, the nanocomposite catalysts had good sedimentation ability and could decant from the suspension in about 10-20 min, while the pure TiO2 did not decant after 8 h.In the forth and the fifth chapter, the effects of preparing conditions such ascalcination temperature, Ti/bentonite and initial pH on the textual characterization?and the photoactivity were studied. The final inserted Ti species of the entire composites prepared under different conditions were TiO: as proved by XPS. All the pillared materials were found thermally stable up to 973 K. The dOOl basal spacings of the composite catalyst decreased with the increase in calcination temperature. The photoability was larger in the order of 773 K treated sample > 973 K> 573 K. The effect of the ratio of Ti/clay on the textural properties was small, while it was obvious on the photoactivity. The photoactivity was the optimum in 3:5. pH was the main factor influencing the amount of Ti supported on the surface of bentonite and the ion exchange ability of inorganic ions in interlayers and particulates with positive charge in the sol. The anatase was found in the sample prepared in pH 2.5 while no crystal titania was found in the sample prepared in pH 1.5. The amount of titania in the interlayer of pH 2.5 was much lower than that of pH 1.5, which was similar to the photoactivity of composite catalyst prepared in different pH condition. Results also indicated that titanium dioxides were highly dispersed in the interlayer and/or on the surface of bentonite. It was that highly dispersed TiOi that played strong...