Photocatalytic Decomposition of p-Nitrophenol over Titanium Dioxides Prepared in Water-in-Carbon Dioxide Microemulsion

摘要

The preparation method of nanosized TiO_2 is mainly comprised of sol-gel, whose main disadvantages are that costly organic solvents are required. The direct hydrolysis of titanium salt and chemical vapor deposition procedure in which TiCl_4 vapor is oxidized at very high temperatures can be used to prepare nanosized TiO_2. In addition, water-in oil (W/O) microemulsions have been successfully employed to obtain ultrafine particles of controlled size of a variety of materials. Carbon dioxide, because of its low cost, low toxicity, and readily accessible critical point is the ideal solvent for use in supercritical fluid extraction techniques. Hydrophilic solutes are only sparingly soluble in carbon dioxide, and so a mechanism for enhancing their solubility in CO_2 is necessary to make CO_2 extraction of hydrophilic solutes commercially feasible. One method to enhance the solubility of hydrophilic solutes in CO_2 is to encapsulate water in CO_2 using surfactants. This requires a surfactant that is both CO_2-philic and hydrophilic. In this paper, we prepared nanosized TiO_2 in water-in-CO_2 microemulsion using ammonium carboxylate perfluoropolyether (PFPE-NH_4) and poly(dimethylaminoethyl methacrylate-block-1H, 1H, 2H, 2H-perfluoroocthylmethacrylate)(PDMAEMA_(2k)-b-PFO MA_(10k)) as surfactants. We also investigated the effect of concentration of surfactants and water as well as the sort of surfactants on the physical properties of nanosized TiO_2 particles. In addition, their photocatalytic activity on the decomposition of p-nitrophenol was also examined as a function of W_o ratio.