Modification of titanium dioxide thin films and preparation of visible light photocatalysts

Two important aspects of the TiO2 photocatalysis were studied in this thesis. The first part reports on the improvement of photocatalytic performance of TiO2 films through approaches such as post-thermal treatment, surface modification and metal doping. The second part describes the fabrication of visible light TiO2 photocatalyts by means of coupling with small band gap semiconductor photo-sensitizers and non-metal doping.; Part I. TiO2 films on stainless steel prepared by dip coating in a nonionic microemulsion solution were investigated. These thin films have been shown to have much higher photocatalytic activity than films on glass substrates. XPS showed that Fe3+ and Fe 2+ ions, which were diffused from stainless steel substrate into TiO 2 films during high temperature calcination, behaved as dopants to significantly affect its photocatalytic activity of the films. The TiO2 films also exhibited excellent photo-induced hydrophilicity and antibacterial effect on the sterilization of Bacillus pumilus.; In addition, through a simple post-thermal treatment of TiO2 thin films on glass with trifluoroacetic acid (TFA), the thin films showed enhancement in the photocatalytic decomposition of acetone in air. XPS, FTIR and PL results revealed that the TFA complex bound on the surface of TiO 2 acted as an electron scavenger, and thus reduced the recombination of photo-generated electrons and holes.; Part II. New approaches have been developed for the fabrication of visible light photocatalysts. MoS2 and WS2 were coupled to TiO2 by an in situ photo-reduction deposition method, taking advantage of the reducing power of TiO2 particles. The synthesis of CdSe sensitized TiO2 using an ultrasound-driven approach was also reported. The photocatalytic degradation of methylene blue and 4-chlorophenol was employed to evaluate their visible light photocatalytic activity. The small band gap semiconductors acting as photo-sensitizers not only extended the spectral response of TiO2 to the visible region but also improved their photocatalytic efficiency. The blue shift in the absorption onset confirmed the size-quantization of photosensitizers, which altered the conduction and valence band levels in the coupled semiconductor systems making it possible to utilize visible light in photocatalysis. (Abstract shortened by UMI.)...