Kinetics and Mechanism of the Enhanced Reductive Degradation of CCl₄ by Elemental Iron in the Presence of Ultrasound

Enhanced rates of sonolytic degradation of CCl 4 in the presence of Fe 0 are demonstrated. In Ar-saturated solutions, the first-order rate constant for CCl 4 degradation is k US = 0.107 min - 1, whereas in the presence of Ar and Fe 0, the apparent first-order rate constant is found to depend on the total surface area of elemental iron in the following fashion: k obs = ( k US + k Fe 0 A Fe 0 ) min - 1, where k US = 0.107 min - 1, k Fe 0 = 0.105 L m - 2 min - 1, and A Fe 0 ) = reactive surface area of Fe 0 in units of m 2 L - 1 . In the coupled ultrasound and iron system, the contribution to the overall degradation rate by direct reaction with Fe 0 results in an overall rate enhancement by a factor of 40. These enhancements are attributed (1) to the continuous cleaning and chemical activation of the Fe 0 surface by the combined chemical and physical effects of acoustic cavitation and (2) to accelerated mass transport rates of reactants to the Fe 0 surfaces. Additional kinetic enhancements are due to the production of H + during the course of the reaction. Furthermore, the concentrations of the principal reaction intermediates, C 2 Cl 6 and C 2 Cl 4, are influenced substantially by the total available surface area of Fe 0 .