The Feasibility Studies for Radical-Induced Decomposition and Demetalation of Metalloporphyrins by Ultrasonication

Abstract

A feasibility study of the decomposition and demetalation of metalloporphyrins by ultrasonic irradiation process in the presence of radical-induced reactions is presented in this paper. Two representative model compounds, NiTPP and VOTPP, were investigated in this ultrasonic process on the laboratory scale. The extent of the decomposition was determined by UV−vis, while the metal analysis was measured by ICP/MS. In the initial investigation, the decomposition of metalloporphyrins, which were dissolved in different solvent−water mixtures, was performed under the ultrasonication process. Among these solvents, the chlorinated-type solvents (e.g., chloroform and dichloromethane) achieved a higher efficiency because they generated more oxidizing species under sonication at 20 kHz frequency. Other additives such as surfactant and hydrogen peroxide, which affect the decomposition efficiency, were also investigated. Under optimal condition, the decomposition efficiency reached about 90% in 1 h for both model compounds. An oxidative intermediate existed for both metalloporphyrins under ultrasonication. The decomposition reaction rates of these two compounds followed pseudo-first-order in reactant concentration and were inhibited by initial feed concentration. The dependence of the rate constants on the different initial concentrations could be determined by the Langmuir−Hinshelwood equation.