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 Bi2O3-TiO2 photocatalyst supported onto commercial powdered activated carbon (Bi2O3-TiO2/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 Bi2O3-TiO2/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 Bi2O3-TiO2/PAC. Both active radicals (SO4 center dot-, h + , center dot O-2(-)) and nonradical singlet oxygen (O-1(2)) and the mediated electron transfer of pristine PAC within Bi2O3-TiO2/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 SO2 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 HCO3, whereas presence of SO42- was less inhibitory and Cl- had no effect. The Bi2O3-TiO2/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 Bi2O3-TiO2/PAC composite for removal of organic micropollutants.