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Kinetics and Mechanism of CCl_4 Photoreductive Degradation on TiO_2: The Role of Trichloromethyl Radical and Dichlorocarbene

Choi, Wonyong and Hoffmann, Michael R. (1996) Kinetics and Mechanism of CCl_4 Photoreductive Degradation on TiO_2: The Role of Trichloromethyl Radical and Dichlorocarbene. Journal of Physical Chemistry, 100 (6). pp. 2161-2169. ISSN 0022-3654. doi:10.1021/jp951431k.

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The mechanism of photoreduction of CCl_4 on illuminated TiO2 surfaces was investigated by selectively trapping transient free radical intermediates. Dichlorocarbene and trichloromethyl radical were trapped with 2,3-dimethyl-2-butene during the photocatalytic degradation of CCl_4. The rate of formation of trapped :CCl_2 and •CCl_3 was found to be a function of [H_2O], pH, [CCl_4], the nature of the dissolved gas, and light intensity. Dissolved oxygen was not essential for the degradation of CCl_4. The production rate of trapped dichlorocarbene showed light intensity dependencies of second, first, and half order with progressively increasing light intensity. A two-electron photoreductive pathway (via dichlorocarbene formation) was found to be the dominant mechanism leading to the full degradation of CCl_4. Since dichlorocarbene is hydrolyzed under basic conditions, the pH and water concentration were found to be integral parameters controlling the complete degradation of CCl_4 to CO, CO_2, and HCl. Kinetic equations describing the formation of trapped dichlorocarbene were derived from a proposed mechanism. The comparison of the predicted rate expression to the observed data suggested that the observed two-electron transfer occurred consecutively.

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Hoffmann, Michael R.0000-0001-6495-1946
Additional Information:© 1996 American Chemical Society. Received: May 23, 1995; In Final Form: October 30, 1995. Financial support from the Advanced Research Projects Agency (ARPA) and the Office of Naval Research (ONR) (Grant N0014-92-J-1901) under the auspices of the Department of Defense-University Research Initiative Program (DOD-URI) is gratefully acknowledged.
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Advanced Research Projects Agency (ARPA)UNSPECIFIED
Office of Naval Research (ONR)N0014-92-J-1901
Department of DefenseUNSPECIFIED
Issue or Number:6
Record Number:CaltechAUTHORS:20150810-152945852
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Official Citation:Kinetics and Mechanism of CCl4 Photoreductive Degradation on TiO2:  The Role of Trichloromethyl Radical and Dichlorocarbene Wonyong Choi and Michael R. Hoffmann The Journal of Physical Chemistry 1996 100 (6), 2161-2169 DOI: 10.1021/jp951431k
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:59367
Deposited By: Ruth Sustaita
Deposited On:11 Aug 2015 16:29
Last Modified:10 Nov 2021 22:19

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