Carbon dioxide radical anion mediated dehalogenation kinetics and mechanisms of halogenated alkanes

Carbon dioxide radical anion (CO2 center dot-) recently becomes appreciated in halogenated contaminants elimination; nevertheless, its application has been restricted by insufficient mechanistic understanding. Herein, we provided a quantitative insight into the kinetics and mechanisms of CO2 center dot- mediated dehalogenation of halogenated alkanes. A CO2 center dot- dominated UV254/H2O2/HCOO- system has been successfully established and demonstrated for effective elimination of 7 kinds of halogenated alkanes (71.3 % to 100 % of removal). Using a laser flash photolysis technology, the second-order rate constants of CO2 center dot- (kCO(2)(center dot-)'') reacting with CCl4, CHCl3 and CH2Cl2 were firstly reported, to be 2.5 x 10(8), 6.2 x 10(7) and 5.8 x 10(6) M(-1)s(-1), respectively. kCO(2)(center dot-)'' presented a significant negative correlation with the lowest unoccupied molecular orbital energy (E-LUMO) of chlorinated alkanes, proving that the enhanced dehalogenation of CO2 center dot- was attributed by direct electron transfer mechanism. A fitting model was developed accordingly for kCO(2)(center dot-)'' prediction. This study also demonstrated that the CO2 center dot- mediated ARP effectively removed halogenated alkanes regardless of pH condition (6.0 similar to 9.0) and bicarbonate concentrations. These findings are significant in advancing the scientific understanding of CO2 center dot- mediated ARP. This reductive process a promising control strategy for halogenated contaminants, such as polyfluoroalkyl substances (PFAS) and halogenated pharmaceuticals.