Solid-state NMR studies of photocatalytic surface chemistry
Abstract
TiO2 has been widely proposed as a promising photocatalytic material for the detoxification of noxious organic pollutants. Significant research efforts using a variety of different analytical techniques are currently being applied to improve our fundamental understanding of the complex surface processes and reaction mechanisms involved in semiconductor photocatalysis. Solid-state NMR spectroscopy was used to perform a detailed investigation of the surface chemistry of TiO2. The adsorption of ethanol on TiO2 was chosen to identify different binding sites on the TiO 2 surface. It was found that ethanol binds to the TiO2 surface in two fashions, either by the formation of hydrogen-bonds with surface hydroxyl groups, or by dissociative chemisorption at coordinatively unsaturated Ti sites to produce Ti-bound ethoxide species. The effect of UV irradiation and surface hydration on the formation and reactivity of surface ethanol species was also investigated. The photocatalytic activities of two supported TiO 2 photocatalysts, TiO2 supported on porous Vycor glass and TiO2-coated optical microfibers, were also assessed using the in situ photooxidation of ethanol. The optical fiber supported catalyst was found to have the highest photocatalytic activity, and a new reactive intermediate, 1,1-diethoxyethane, was observed. In photooxidation reactions of dichloromethane on TiO2 powder, the formation of two unique phosgene species was observed. The second phosgene species is thought to be caused by the participation of lattice oxygen or Cl ions. A second more mobile dichloromethane species was also observed when the catalyst was illuminated. Finally, a series of supported monolayer TiO2 photocatalysts doped with SnO2 were prepared, characterized, and their photocatalytic activities were accessed using the photooxidation of ethanol. The photocatalytic activities of the SnO2 containing catalysts were lower than TiO 2 alone due to slower conversion of acetaldehyde to acetic acid and possible poisoning of the catalyst surface.
Degree
Ph.D.
Advisors
Raftery, Purdue University.
Subject Area
Analytical chemistry
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