Highly dispersed ZIF-67 derived cobalt nanoparticle supported on g-CN for rapid degradation of sulfamethoxazole by Fenton-like oxidation: Enhanced adsorption and electron transfer.

Zeolitic imidazolate framework (ZIF-67) derivatives have emerged as promising Fenton-like catalysts due to their tunable structural regulation and multi-element composition. However, the rational design of ZIF-67-derived materials with highly exposed metal active sites remains a critical challenge. Here, a carbon nitride (g-CN) supported ZIF-67 derivatives (Co-GNC), featuring highly dispersed cobalt (Co) nanoparticles, was developed for peroxymonosulfate (PMS) activation to degrade sulfamethoxazole (SMX). The physicochemical properties of the Co-GNC were systematically characterized using advanced analytical techniques. Batch experiments were conducted to investigate the effects of various parameters on SMX removal efficiency. The results revealed that Co-GNC-0.6, with an optimal g-CN loading (0.6 g), exhibited exceptional catalytic performance. It achieved 82.86 % SMX removal (k = 0.2434 min) with 10 min. The negative influence of coexisting ions on SMX removal followed the order: NO < NH < Cl < SO < HPO < HCO. Co-GNC-0.6 demonstrated remarkable stability and recyclability for SMX removal, and demonstrated broad-spectrum applicability by removing over 70 % of other antibiotics (e.g., tetracycline, levofloxacin, and ciprofloxacin). Quenching experiments, electron paramagnetic resonance (EPR), and electrochemical analyses revealed that SMX degradation involved a synergistic mechanism of free radicals (O), non-free radicals (O), and direct electron transfer, achieving 68.5 % total organic carbon (TOC) removal. The large specific surface area of g-CN facilitated initial adsorption of SMX onto the catalyst surface. Moreover, g-CN inhibited agglomeration of Co nanoparticles, ensuring high dispersion and exposing more active sites for PMS activation. Furthermore, g-CN increased the charge density of the catalyst and reduced charge transfer resistance, thereby accelerating electron transfer. Density functional theory (DFT) calculations confirmed that g-CN enhanced PMS adsorption on Co-GNC-0.6 and significantly promoted interfacial electron transfer. Based on identified SMX degradation intermediates, four potential degradation pathways were proposed. Environmental Chemistry and SAR Tool (ECOSAR) prediction indicated a significant reduction in the biological toxicity of degradation products. This study provides a novel strategy for designing highly efficient PMS activators with optimized metal dispersion and active site exposure for rapid removal of SMX.