Peroxymonosulfate activation by iron-carbon composite derived from coal gasification slag for sulfamethoxazole removal: Performance evaluation and mechanism insight

A novel iron-carbon (Fe-C) composite was fabricated using coal gasification slag (CGS) as the feedstocks and applied in sulfamethoxazole (SMX) degradation via peroxymonosulfate (PMS) activation. The optimized Fe-C composite (CGS-1000) had excellent catalytic ability among the reported metal-C catalysts, showing a superior SMX degradation capacity (91.1 %) and kinetic reaction rate (0.0177 min−1) within 90 min under the condition of 0.2 g·L−1 CGS-1000, 2.0 mM PMS at ambient pH (6.3). Characterization results illustrated that the relatively larger surface area (102.50 m2·g−1), pore size (3.93 nm), and higher carbon defectiveness (ID/IG = 1.48) of CGS-1000 promoted its SMX degradation performance. XPS and FTIR spectrum revealed that PMS was mainly activated by Fe species and oxygen-containing functional groups (CO, C-OH) on the carbon matrix for the generation of reactive oxygen species (ROS). Notably, surface-bounded radicals (SO4−, OH), singlet oxygen (1O2), and direct electron transfer were primarily involved in the CGS-1000/PMS system, of which the relative contributions to SMX oxidation were calculated to be 25.8 %, 49.5 %, and 12.5 %, respectively. The excellent degradation efficiency should be attributed to the simultaneous SMX oxidation both in solution and on the surface of CGS-1000 through these three oxidation pathways. Finally, four SMX degradation pathways were proposed based on the twelve intermediates detected by LC-MS. The toxicity of the by-products of SMX was alleviated according to the quantitative structure–activity relationship analysis. Overall, these results suggested that CGS-1000 was a high-efficiency PMS catalyst for SMX degradation and provided new insights into the design of other solid waste-derived catalysts.