Environmental Science and Technology p. 3011 - 3016 (1998)
Update date:2022-08-17
Topics:
Hung, Hui-Ming
Hoffmann, Michael R.
Enhanced rates of sonolytic degradation of CCl4 in the presence of Fe0 are demonstrated. In Ar-saturated solutions, the first-order rate constant for CCl4 degradation is k(US) = 0.107 min-1, whereas in the presence of Ar and Fe0, 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)0A(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 Fe0 in units of m2 L-1. In the coupled ultrasound and iron system, the contribution to the overall degradation rate by direct reaction with Fe0 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 Fe0 surface by the combined chemical and physical effects of acoustic cavitation and (2) to accelerated mass transport rates of reactants to the Fe0 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, C2Cl6 and C2Cl4, are influenced substantially by the total available surface area of Fe0. Enhanced rates of sonolytic degradation of CCl4 in the presence of Fe0 are demonstrated. In Ar-saturated solutions, the first-order rate constant for CCl4 degradation is kUS = 0.107 min-1, whereas in the presence of Ar and Fe0, the apparent first-order rate constant is found to depend on the total surface area of elemental iron in the following fashion: kobs = (kUS+kFe0AFe0) min-1, where kUS = 0.107 min-1, kFe0 = 0.105 L m-2 min-1, and AFe0) = reactive surface area of Fe0 in units of m2 L-1. In the coupled ultrasound and iron system, the contribution to the overall degradation rate by direct reaction with Fe0 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 Fe0 surface by the combined chemical and physical effects of acoustic cavitation and (2) to accelerated mass transport rates of reactants to the Fe0 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, C2Cl6 and C2Cl4, are influenced substantially by the total available surface area of Fe0.
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