Preparation of Co/S co-doped carbon catalysts for excellent Methylene Blue degradation

To effectively activate peroxymonosulfate (PMS) for methylene blue (MB) degradation purposes, S and Co co-doped carbon catalysts were prepared by pyrolysing MOF-71 and thiourea mixtures at 800oC at the mass ratio of MOF-71 to thiourea of 1:0.1. 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 95.60wt% MB (50 mg/L) within 4 minutes(k=0.78), which was faster than that originated from the direct grinding way (MOF-DGP, 80.97wt%, k=0.39). X-ray photoelectron spectroscopy (XPS) showed that the Co-S site of MOF-AEP (43.39%) was less than that of MOF-DGP(54.73%), and the proportion of C-S-C in MOF-AEP(13.56%) was higher than that of MOF-DGP (10.67%). Density functional theory (DFT) calculations showed 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). It was thus speculated that the C-S-C sites might contribute more in activating PMS compared with Co-S. Furthermore, the degradation parameters including pH and MOF-AEP dosage were also investigated. Finally, radical quenching experiments and electron paramagnetic resonance (EPR) measurements revealed that 1O2 might be the primary catalytic species whereas the •O2− might be the secondary ones in degrading MB.