Photocatalytic degradation of organic contaminants: Novel catalysts and processes

• Main Author: Davydov, Lev
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2001
• Subjects: Chemical engineering; Electrical engineering
• ISBN: 049353024X; 9780493530246

Photocatalysis has recently emerged as an advanced oxidation process. The present dissertation aims at the practical increase of the energy efficiency of photocatalysis using fundamental tools. A comprehensive kinetic model was developed to describe primary photocatalytic processes taking place on the surface of semiconductors. The steady-state assumption for all the intermediate species in the system allowed to find the lumped kinetic parameters and elucidate the relative extent of electron-hole recombination reactions. It is important to utilize single-stage oxidation reactions to test this kinetic model and obtain kinetic parameters. This simple method also allowed to experimentally determine the rates of radical generation as well as the rate of electron-hole recombination for a number of commercial titania photocatalysts. When interfaced with the continuous flow reactor design, the model allowed to predict the optimal radiation profiles in photoreactors, which would significantly increase the reactor output. Such profiles are represented by a combination of exponential functions, and they prescribe more radiation at the beginning of the reactor in comparison with that at the end. Furthermore, it was found that when a continuous-flow reactor with recycle, the use of the optimal profile can produce a major enhancement of the output in comparison with the uniformly illuminated photoreactor. The expansion of the working range of photocatalysts to enable them to utilize visible light was also undertaken. To achieve this, a combination of doping and sensitization properties was needed. It was found that titania-loaded transition metal MCM-41 materials can allow for such combination. The heterojunction with the transition metal substituted MCM-41 works as a “sensitizer” for the titania deposit, while the extraframework transition metal inclusion can diffuse inside the titania loading and work as a dopant. The latter allows to effectively utilize visible light to perform photocatalytic reactions. Similar effect of sensitization was found for Cd-MCM-41, which enhances the photoactivity of titania in ultraviolet light. Conclusively, it has been shown that the use of optimal reactor design as well as novel catalysts containing active supports can significantly increase the reaction rates and exclude the dependence of the process on the artificial sources of energy.