Degradation of malathion in the solution of acetyl peroxyborate activated by carbonate: Products, kinetics and mechanism.

The degradation process of malathion in the acetyl peroxyborate (APB) solution of different APB/malathion molar ratio and in the carbonate-activated APB (APB/CO32-) solution of different pH was studied by 31P NMR technology. In the APB solution, all malathion could be degraded in 47.5 min when the molar ratio of APB/malathion was 60. CO32- could effectively activate APB to degrade all malathion in 10 min at pH of 10 when APB/malathion was 10, which was obviously higher than in APB solution. 1O2, •O2-, •OH and carbon-centered radicals (RC•) could be produced in the APB/CO32- solution, and the degradation of malathion was mainly affected by RC•. The degradation mechanism of malathion in the APB/CO32- solution was proposed based on the research results of malathion degradation process by 31P NMR and active species quenching test, which involves two steps: the first step is the oxidation of malathion to malaoxon by RC•, and the second step is the hydrolysis of malaoxon to dimethyl phosphate via hydroxyl anions nucleophilic addition.