Synthesis of titanium dioxides in water-in-carbon dioxide microemulsion and their photocatalytic activity

Titania nanoparticles were prepared by controlled hydrolysis of titanium tetraisopropoxide (TTIP) in water-in-carbon dioxide microemulsion using ammonium carboxylate perfluoropolyether (PFPE-NH4) as a surfactant. The physical properties were examined by thermogravimetric-differential thermal analysis (TGA-DTA), X-ray diffraction (XRD) and transmission electron microscope (TEM). In addition, the photocatalytic decomposition of p-nitrophenol was also investigated using batch reactor in the presence of UV light. It is shown that the residual hydroxyl group and the organic compounds were completely removed in the calcining temperature from 250 to 450 degreesC and the amorphous phase transformed to anatase structure above 450 degreesC. The crystallinity and crystallite size of nanoparticles produced in water-in-carbon dioxide increased with an increase of W-o ratio. In the photocatalytic decomposition of p-nitrophenol, the photocatalytic activity was mainly determined by the crystallite size of titania and the reaction rate increased with a decrease of crystallite size. (C) 2003 Elsevier Science B.V. All rights reserved.