Preparation of Co/S co-doped carbon catalysts for excellent methylene blue degradation

S and Co co-doped carbon catalysts were prepared via pyrolysis of MOF-71 and thiourea mixtures at 800°C at a mass ratio of MOF-71 to thiourea of 1:0.1 to effectively activate peroxymonosulfate (PMS) for methylene blue (MB) degradation. The effects of two different mixing routes were identified on the MB degradation performance. Particularly, the catalyst obtained by the alcohol solvent evaporation (MOF-AEP) mixing route could degrade 95.60% MB (50 mg/L) within 4 min (degradation rate: K = 0.78 min^–1), which was faster than that derived from the direct grinding method (MOF-DGP, 80.97%, K = 0.39 min^–1). X-ray photoelectron spectroscopy revealed that the Co–S content of MOF-AEP (43.39at%) was less than that of MOF-DGP (54.73at%), and the proportion of C–S–C in MOF-AEP (13.56at%) was higher than that of MOF-DGP (10.67at%). Density functional theory calculations revealed that the adsorption energy of Co for PMS was −2.94 eV when sulfur was doped as C–S–C on the carbon skeleton, which was higher than that when sulfur was doped next to cobalt in the form of Co–S bond (−2.86 eV). Thus, the C–S–C sites might provide more contributions to activate PMS compared with Co–S. Furthermore, the degradation parameters, including pH and MOF-AEP dosage, were investigated. Finally, radical quenching experiments and electron paramagnetic resonance (EPR) measurements revealed that ¹O₂ might be the primary catalytic species, whereas · O²⁻ might be the secondary one in degrading MB.