Activation mechanism of peroxymonosulfate by biochar for catalytic degradation of 1,4-dioxane: Important role of biochar defect structures

Carbonaceous materials have been emerged as promising metal-free catalysts to activate peroxymonosulfate (PMS) for the degradation of organic contaminants. In the present study, a low-cost carbonaceous material, pine needle biochar was prepared under the oxygen limited pyrolyzation process and applied to activate PMS for the catalytic degradation of potentially carcinogenic 1,4-dioxane. Based on the batch experiments, the pyrolysis temperature has a significant influence on the potency of biochar to activate PMS. Within the biochar/PMS system, the degradation efficiencies of 1,4-dioxane were increased from 4.1 to 84.2% when the biochar pyrolysis temperatures were increased from 300 °C to 800 °C. Electron paramagnetic resonance (EPR) study and the quenching experiment verified that the dominant free radical within the system of biochar/PMS was OH. The EPR combined X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) and Raman analysis implied that the defect of biochar contributed to the generation of SO4− and OH and high pyrolysis temperatures would eliminate the excess of oxygen functional groups in biochar, which could modulate and transform sp3 carbons, generating more defect structures, therefore, enhancing the activation potency of biochar towards PMS. Simultaneously, five major intermediates were identified and three possible degradation pathways were proposed in this study. In addition, 71.4% and 57.5% of 1,4-dioxane removal rates were achieved in 1,4-dioxane contaminated tap water and groundwater, indicating that biochar activating PMS is a promising technique for the remediation of 1,4-dioxane contaminated water.