Catalytic activation of different oxidants including peroxymonosulfate (PMS), peroxydisulfate (PDS), hydrogen peroxide (H2O2) and ozone (O3) by MnO2 for degradation of sulfachloropyridazine (SCP) was investigated and the effects of different crystalline phases of MnO2 including nanowire α-MnO2, nanorod β-MnO2, nanofiber γ-MnO2, and nanosphere δ-MnO2 on catalytic ozonation of SCP were also studied. The SCP degradation and total organic carbon removal indicated that the oxidation efficiency of the peroxide oxidants followed an order of O3/MnO2 > PMS/MnO2 > PDS/MnO2 > H2O2/MnO2. In catalytic ozonation, SCP degradation rate constants of different MnO2 phases followed an order of δ-MnO2 > α-MnO2 > γ-MnO2> β-MnO2. Electron paramagnetic resonance (EPR) suggested that hydroxyl radicals (·OH) and singlet oxygen (1O2) might be more significant for SCP degradation than sulfate (SO4·-) and superoxide (·O2-) radicals. Radical competition experiments demonstrated that 1O2 and ·OH contributed to 63.16% and 28.07%, respectively, for the catalytic ozonation of SCP. It was also found that more oxygen vacancies, specific surface area and exposure of MnO6 edges could facilitate the activation of O3 for 1O2 and ·OH productions and SCP degradation. The degradation pathways of SCP could mainly follow the cleavage of S-C or S-N bond and dechlorination, accompanied by hydroxylation and oxidation.
Keywords: Crystal structures; MnO(2); Ozonation; Peroxide oxidants; Sulfachloropyridazine degradation.
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