Welcome to the new version of CaltechAUTHORS. Login is currently restricted to library staff. If you notice any issues, please email coda@library.caltech.edu
Published January 1997 | public
Journal Article

Novel Photocatalytic Mechanisms for CHCl_3, CHBr_3, and CCl_3CO_2^-Degradation and the Fate of Photogenerated Trihalomethyl Radicals on TiO_2


The photocatalytic degradation of CHCl_3, CHBr_3, CCl_4, and CCl_3CO_2^- is investigated in aqueous TiO_2 suspensions. A common intermediate, the trihalomethyl radical, is involved in the degradation of each substrate except for CCl_3CO_2^-. CHCl_3 and CHBr_3 are degraded into carbon monoxide and halide ions in the absence of dissolved oxygen. The anoxic degradation proceeds through a dihalocarbene intermedi ate, which is produced by sequential reactions of the haloform molecule with a valence band hole and a conduction band electron. Carbon dioxide and halide ion are formed as the primary products during CHCl_3 degradation in the presence of oxygen. Under these conditions, the trihalomethyl radicals react rapidly with dioxygen. At pH > 11, degrada tion of the haloforms is enhanced dramatically. This enhancement is ascribed to photoenhanced hydrolysis. The secondary reactions of the trichloromethyl radical generated during CCl_4 photolysis is strongly influenced by the nature of the electron donors. Both •CCl_3 and Cl^- production increase substantially when 2-propanol is present as an electron donor. A new photocatalytic mechanism for CCl_3CO_2^- degradation, which involves the formation of a dichlorocarbene intermediate, is proposed.

Additional Information

© 1996 American Chemical Society. Received for review February 20, 1996. Revised manuscript received August 16, 1996. Accepted August 26, 1996. We thank the Advanced Research Projects Agency (ARPA) and the Office of Naval Research (ONR) {N0014-92-J-1901} for financial support. Wealso appreciate the help from Robert Rossi and Janet Kesselman in GC analysis.

Additional details

August 19, 2023
October 23, 2023