Synergistically boosting sulfamerazine degradation via activation of peroxydisulfate by photocatalysis of Bi2O3-TiO2/PAC under visible light irradiation
Photocatalysis-activated sulfate-radical advanced oxidation process (SR-AOP) is an effective approach to remove organic micropollutants from water. Here, we tested a photocatalysis-activated SR-AOP in which peroxydisulfate (PDS) was activated by composites of Bi 2 O 3 -TiO 2 photocatalyst supported onto commercial powdered activated carbon (Bi 2 O 3 -TiO 2 /PAC) under visible light irradiation. This “Vis-Cata-PDS” treatment exhibited outstanding degradation performance (97.96% removal) towards sulfamerazine (SMZ) following optimized reaction conditions of 0.1 g/L Bi 2 O 3 -TiO 2 /PAC and 0.1 g/L PDS at pH of 7. Synergistic effects were observed between the visible-light photocatalytic activation of PDS via direct electron transfer and nonradical PDS activation over pristine PAC within Bi 2 O 3 -TiO 2 /PAC. Both active radicals (SO 4 ·− , h + , ·O 2 − ) and nonradical singlet oxygen ( 1 O 2 ) and the mediated electron transfer of pristine PAC within Bi 2 O 3 -TiO 2 /PAC were contributed to SMZ degradation. Based on intermediates identified by Liquid Chromatograph-Mass Spectrometer (LC-MS) combined with density functional theory (DFT) calculations, three degradation pathways were proposed and that were mostly attributed to SO 2 extrusion/Smiles-type rearrangement and S-N bond cleavage, and toxicity of intermediates were effectively alleviated. An inhibitory effect on SMZ degradation was observed for presence of HCO 3 − , whereas presence of SO 4 2− was less inhibitory and Cl − had no effect. The Bi 2 O 3 -TiO 2 /PAC composite displayed excellent reusability and stability, and it was effective towards a number of tested micropollutants (sulfadiazine, sulfamethoxazole, ciprofloxacin, bisphenol A and methyl orange) and in real water matrixes. This work offers deep insights into the nonradical oxidation mechanism and application of Vis-Cata-PDS over a Bi 2 O 3 -TiO 2 /PAC composite for removal of organic micropollutants.
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