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Photoreductive Mechanism of CCl_4 Degradation on TiO_2 Particles and Effects of Electron Donors

Choi, Wonyong and Hoffmann, Michael R. (1995) Photoreductive Mechanism of CCl_4 Degradation on TiO_2 Particles and Effects of Electron Donors. Environmental Science and Technology, 29 (6). pp. 1646-1654. ISSN 0013-936X. doi:10.1021/es00006a031.

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The photoreductive degradation of CCl_4 in TiO_2 particulate suspensions in the presence of a variety of organic electron donors (alcohols, carboxylic acids, and benzene derivatives) has been examined. The rate of CCl_4 dechlorination can be enhanced significantly when alcohols and organic acids are used as electron donors. Alcohols with α-hydrogens show complex behavior due to the formation of intermediate α-hydroxyalkyl radicals, which directly reduce CCl_4. Kinetic isotope effects and structurere-activity relationships show that hydrogen-abstraction by hydroxyl radicals plays an important role in the hole-scavenging mechanism. The pH of the TiO_2 suspension influences the rate of CCl_4 reduction either by altering the electrostatic interactions of electron donors on the TiO_2 surface or by changing the reduction potential of the conduction band electron in a Nernstian fashion. It is demonstrated that CCl_4 can be fully degraded under both oxic and anoxic conditions. CHCl_3, C_2Cl_4, and C_2Cl_6 are detected as intermediates during photolysis at pH 2.8 while no intermediates are formed at pH 12.4. A photodegradation mechanism of CCl_4 that includes both one-electron and two-electron transfer processes is proposed. Dichlorocarbene, which is formed through a two-electron reduction of CCl_4, is directly trapped during the photolysis.

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Hoffmann, Michael R.0000-0001-6495-1946
Additional Information:© 1994 American Chemical Society. Received for review October 31, 1994. Revised manuscript received February 28, 1995. Accepted March 8, 1995. We are grateful to ARPA and ONR (N0014-92-J-1901) for financial support. We appreciate the help from Inez Hua, Patrick Lang, Scot Martin, Janet Kesselman, and Nicole Peill in various aspects of this research. Comments from anonymous reviewers were valuable.
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Advanced Research Projects Agency (ARPA)UNSPECIFIED
Office of Naval Research (ONR)N0014-92-J-1901
Issue or Number:6
Record Number:CaltechAUTHORS:20150810-083411600
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Official Citation:Photoreductive Mechanism of CCl4 Degradation on TiO2 Particles and Effects of Electron Donors Wonyong Choi and Michael R. Hoffmann Environmental Science & Technology 1995 29 (6), 1646-1654 DOI: 10.1021/es00006a031
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:59333
Deposited By: Ruth Sustaita
Deposited On:10 Aug 2015 18:28
Last Modified:10 Nov 2021 22:18

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