Insights into atrazine degradation by thermally activated persulfate: Evidence from dual C-H isotope analysis and DFT simulations

SO4 center dot--assisted oxidation was of great concern and the accurate interpretation of reaction pathway was crucial. Innovatively, this study introduced compound-specific isotope fractionation analysis (CSIA) into atrazine (ATZ) degradation by heat-activated persulfate (PS), in order to provide "in-situ" and "fingerprinted" analysis of reaction contribution and bond cleavage process based on isotope fractionation. As results, radical oxidants including SO(4)(center dot-)and center dot OH were generated through thermal activation of PS, and proved to play dominate roles in ATZ degradation. Inconceivably, the isotope fractionation by single SO(4)(center dot- )dominated reaction showed weak and positive C isotope fractionation, with epsilon(C) of 1.58 parts per thousand at pH 4 and 0.65 parts per thousand at pH 7, respectively. Reactions by single SO(4)(center dot-)and center dot H can be distinguished resulting from their significantly different epsilon and A(C/H) values. Changes of delta C-13 and delta H-2 values during ATZ degradation by heat-activated PS followed Rayleigh equation well, with the epsilon(C), epsilon(H) and A(C/H) values of -1.5 parts per thousand, -21.1 parts per thousand, 6.60 at pH 4 and -2.7 parts per thousand, -36.6 parts per thousand, 10.02 at pH 7 respectively. The relative contribution of SO(4)(center dot- )radical to ATZ degradation was ca.100 % at pH 4 and 83.9 % at pH 7. The isotope fractionation study and DFT calculations suggested that single electron transfer with the cleavage of C-Cl bond was dominated and displayed inverse C isotope fractionation for SO(4)(center dot- )oxidation, which was different from that of center dot OH oxidation and more selective to dehalogenate reaction. This research emphasized the promising technology of CSIA, which can achieve accurate identification of reaction contribution and pathways in advanced oxidation process.