Hm. Hung et Mr. Hoffmann, KINETICS AND MECHANISM OF THE ENHANCED REDUCTIVE DEGRADATION OF CCL4 BY ELEMENTAL IRON IN THE PRESENCE OF ULTRASOUND, Environmental science & technology, 32(19), 1998, pp. 3011-3016
Enhanced rates of sonolytic degradation of CCl4 in the presence of Fe-
0 are demonstrated. In Ar-saturated solutions, the first-order rate co
nstant for CCl4 degradation is k(US) = 0.107 min(-1), whereas in the p
resence of Ar and Fe-0, the apparent first-order rate constant is foun
d to depend on the total surface area of elemental iron in the followi
ng fashion: k(obs) = (k(US) + k(Fe0)A(Fe0)) min(-1), where k(US) = 0.1
07 min(-1), k(Fe0) = 0.105 L m(-2) min(-1), and A(Fe0))= reactive surf
ace area of Fe-0 in units of m(2) L-1. In the coupled ultrasound and i
ron 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 (I)to the continuous cleanin
g and chemical activation of the Fe-0 surface by the combined chemical
and physical effects of acoustic cavitation and (2) to accelerated ma
ss transport rates of reactants to the Fe-0 surfaces. Additional kinet
ic enhancements are due to the production of H+ during the course of t
he reaction. Furthermore, the concentrations of the principal reaction
intermediates, C2Cl6 and C2Cl4, are influenced substantially by the t
otal available surface area of Fe-0.