Role of radical and non-radical pathway in activating persulfate for degradation of p-nitrophenol by sulfur-doped ordered mesoporous carbon

A new application of heteroatom doped ordered mesoporous carbon as metal-free catalyst was proposed in this study. Sulfur-doped ordered mesoporous carbons (S-OMCs) with different sulfur doping amount were synthesized to activate persulfate (PS) for p-nitrophenol (PNP) degradation. Thereinto, the activation effect of 2.0 wt% S-OMC improved most significantly after it reached the adsorption equilibrium, and the removal rate of PNP was 82.02%. The optimal experimental effect can be achieved at room temperature and unadjusted pH (pH = 6), retrenching energy and chemical input for practical applications. Higher temperatures could cause radical quenching, while electrostatic repulsion existed between S-OMC and PNP at pH > 6.03, which led to a reduction of PNP removal. Moreover, the structural features and surface characters of S-OMC were studied and found that the defect structure and surface functional groups had noticeable influence on the reusability of S-OMC. More importantly, both radical activation and non-radical activation were detected, and non-radical activation predominated in the S-OMC/PS system. The radical pathway oxidized pollutant by generating (OH)-O-center dot, SO4 center dot-, and O-2(center dot-). Among them, 'OH was dominated. While the non-radical pathway attacked contaminant by continuous electron transport between PNP, S-OMC and PS. This research provided a new perspective on the application of heteroatom doped ordered mesoporous carbon and presented an easy and effectual way for the removal of organic contaminants.