Enhanced photocatalytic degradation of 2-thiobenzimidazole by the tris(8-quinolinolato)cobalt(iii) complex through peroxide adduct formation: theoretical and experimental investigations

Abstract

Photo-initiated oxidative degradation of 2-thiobenzimidazole (2-TBI) was studied using different semiconducting metal complexes derived from 8-hydroxyquinoline with the general formula, [MQ₃C₂H₅OH] [Q = 8-quinolinolato anion; M = Cr³⁺, (CrQ3); Co³⁺, (CoQ3); Fe³⁺, (FeQ3)]. The degradation kinetics was monitored via UV-vis spectroscopy perceiving the changes in absorbance to subtract. The effect of pH and visible light irradiation on degradation was studied observing a significant increment in the oxidation rate with the presence of visible light whenever CoQ3 is used as a catalyst. By using density functional theory (DFT), it was found that the transition state energy of the adduct formed between CoQ3 and H₂O₂ is very low compared with other studied catalysts, which activates the formation of ˙OH radicals from H₂O₂ increasing the 2-TBI degradation rate. In addition, a thermodynamically feasible degradation mechanism was proposed by calculating energy barriers involved in the 2-TBI oxidation pathway.