| Titanium dioxide, TiO2, is used in a variety of environmental applications. In particular, its use to convert toxic wastes to benign materials, via photocatalytic oxidation or reduction reactions, is of considerable interest at this time. Since this material is relatively inexpensive, non-toxic and environmentally acceptable, studies to improve the photocatalytic properties of TiO2 represent an active research area. Research goals include shifting the TiO2 absorption spectrum to longer wavelengths, and enhanced catalytic lifetime with respect to surface poisoning reactions. Despite many prior studies involving surface modification of TiO2 in attempts to achieve these goals, success in this area has been relatively limited. This simply reflects the fact that such surface modifications represent an exceedingly difficult challenge from the experimental standpoint in that spontaneous aggregation of the nanoparticle size TiO2 severely limits the efficacy of any conventional surface modification process.; This dissertation examines the utility of plasma enhanced chemical vapor deposition (PECVD) technology to improve TiO2 photocatalytic activity. It represents the first study to utilize plasma depositions for this purpose. To help minimize aggregation, a rotating reactor was employed to provide constant particle agitation during the plasma coating. Several monomers were employed during the PECVD step, undergoing plasma induced polymerizations and depositing as thin films on the TiO2 particles. The surface modified particles were subsequently characterized and evaluated. This included Fourier Transform Infrared and X-Ray Photoelectron Spectroscopy, to obtain chemical compositional information; X-Ray Diffraction, to monitor crystal structures; and, Atomic Force Microscopy, Scanning Electron Microscopy and Transmission Electron Microscopy, to examine surface morphologies. Most important, direct evaluations of photocatalytic activities of plasma surface modified, versus that of untreated, materials were carried out.; The results suggest that the PECVD approach is a viable new general approach to controlled surface modification of nanosize particles. Specifically, tin oxide and fluorinated surface modified TiO2 nanoparticles exhibited significantly improved photocatalytic activities, compared to the untreated materials. Enhanced activity was demonstrated for both photocatalytic oxidation, reduction reactions using an organic dye and Cr (VI), respectively, as model systems, these processes carried out in aqueous solutions at normal pH and ambient temperature. |
