Enhancement and modeling of the photocatalytic degradation of benzoic acid

Abstract

The kinetics of the photocatalytic degradation of benzoic acid in the presence of TiO2 has been investigated experimentally and theoretically. The effects of catalyst loading, initial concentration of benzoic acid and the electron acceptors; H2O2, K2S2O8 and OXONE on the degradation rate have been examined. A pseudo-first order kinetic model has been used to describe the results. With the intention of predicting the primary intermediates and the product distribution, geometry optimizations of the reactants, product radicals and transition state complexes have been performed with the semi-empirical PM3 and DFT/B3LYP/6-31G* methods. Solvation effects have been computed by DFT calculations at the B3LYP/6-31G* level using COSMO as the solvation model. Based on the results of the quantum mechanical calculations, the rate constants of the four possible reaction paths have been calculated by means of Transition State Theory. A branching ratio for each of the reaction paths has been calculated and the product distribution for the degradation reaction has been determined. The results show that ortho-, meta- and para-hydroxybenzoic acids are formed as the primary intermediates in the photocatalytic degradation of benzoic acid.