Tu Xingzhao,Zhou Lihong,Li Zhijie,Lei Ning,Zeng Qingle
Abstract The carbon-heteroatom bond formation is an important research field. Transition-metal-free synthesis of medicinally important heterocycles avoids products of transition metal contamination, and thus it is an environmentally friendly and cost-saving process. A transition-metal-free domino C-S/C-N formation for the synthesis of imidazobenzothiazines from 2-mercaptobenzimidazoles and 2-halobenzyl bromides is developed. The desired products were obtained in good to excellent yields. The mechanism of domino nucleophilic substitution (S N 2) and nucleophilic aromatic substitution (S N Ar) is proposed. Graphical abstract
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 1 O 2 might be the primary catalytic species, whereas ·O 2− might be the secondary one in degrading MB.
High efficient and stable activator is desired for the sulfate radical-based wastewater treatment. Cobalt sulfide and cobalt oxide have high catalytic activity for peroxymonosulfate (PMS), but poor stability. Here, a novel composite, nano Co 9 S 8 and CoO encapsulated by nitrogen and sulfur co-doped sludge-derived biochar (CoO/Co 9 S 8 @N-S-BC) was synthesized, characterized and applied for activating PMS. The results showed that CoO/Co 9 S 8 @N-S-BC can effectively activate PMS for sulfamethoxazole (SMX) degradation, and 0.08 mM of SMX could be completely degraded within 10 min. The influencing factors, such as pH, temperature, chloridion, carbonate and humic acid were investigated. The SMX degradation conformed to pseudo first-order kinetics with rate constant of 0.379 min −1 . Sulfate radicals (dominant) and hydroxyl radicals contributed to SMX degradation. Carbon defects, pyridinic N, quaternary N, the carbon atoms next to pyridinic N, C O groups, -C-S-C and Co(II), all contributed to PMS activation.
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