Effects of Periodic Illumination and Aqueous/Organic Interfacial Surface Area on Chain Propagation of CCl3F Reduction

Abstract

Periodic illumination and changes in the interfacial aqueous-CFC surface area reveal interesting features of the propagation process occurring during the photoinitiated chain reduction of trichlorofluoromethane (CFC 11) to CHCl2F and Cl– in TiO2 suspensions containing HCO2– ions. Formate ions serve as hole scavengers on the TiO2 surface and react with •CCl2F radicals to form HCCl2F and •CO2–. Carboxyl radicals are capable of propagating the chain reaction in the solution phase by reducing CCl3F. Chain reduction of CCl3F continues after illumination has ceased, and the postirradiation reactions constitute 10% or more of the total Cl– yield. The dark reduction of CFC 11 provides further support to the proposed mechanism in which •CCl2F and •CO2– ions function as chain carriers. The reaction rate measured during a period of illumination is affected by the length of the preceding dark period. In addition, the rate of CCl3F reduction is significantly enhanced by the presence of excess CFC 11, which forms a sec...