Synthesis of S, N co-doped porous carbons from polybenzoxazine for CO₂ capture

S, N co-doped porous carbons were synthesized from polybenzoxazine through solidification, carbonization and KOH activation using 4-cyanophenol, thiourea and formaldehyde as the monomers and a triblock copolymer (Pluronic F127) as a soft template. The samples were characterized by FT-IR, SEM, N₂ adsorption, elemental analysis and XPS. Results indicate that the activated samples had high surface areas of 1 511.6-2 385.1 m² g^-1 with a large number of micropores and abundant sulfur and nitrogen functionalities. The templated samples had apparently lower contents of sulfur, nitrogen and oxygen than the un-templated ones due to the easy escape of volatile sulfur, nitrogen and oxygen compounds during carbonization and KOH activation. CO₂ uptake had contributions from both physical and chemical adsorption and depended on the volume of narrow micropores less than 0.8 nm and the numbers of basic sulfur and nitrogen functional groups. The un-templated sample activated at 600℃ had the highest CO₂ uptakes of 6.96 and 4.55 mmol g^-1 under 1 bar at 0 and 25℃, respectively, and was highly selective for CO₂/N₂ separation and had a high recyclable stability for CO₂ capture.