Design of biomass-based N, S co-doped porous carbon via a straightforward post-treatment strategy for enhanced CO2 capture performance

Biomass-based adsorbents are considered to have great potential for CO2 capture due to their low cost, high efficiency and exceptional sustainability. The aim of this work is to design a simple method for preparing biomass-based adsorbents with abundant active sites and large numbers of narrow micropores, so as to enhance CO2 capture performance. Herein, N, S co-doped porous carbon (NSPC) was created utilizing walnut shell-based microporous carbon (WSMC) as the main framework and thiourea as N/S dopant through physical grinding and post-treatment process at a moderate temperature without any other reagents and steps. By altering the post-treatment parameters, a series of porous carbons with varying physico-chemical properties were prepared to discuss the roles of microporosity and N/S functional groups in CO2 adsorption. NSPC with narrow micropore volume of 0.74 cm3 g-1, N content of 4.89 % and S contents of 0.71 % demonstrated the highest CO2 adsorption capacity of 7.26 (0 °C) and 5.51 mmol g-1 (25 °C) at 1 bar. Meanwhile, a good selectivity of binary gas mixture CO2/N2 (15/85) of 29.72 and outstanding recyclability after ten cycles of almost 100 % adsorption capacity retention were achieved. The proposed post-treatment method was beneficial in maintaining the narrow micropores and forming N/S active sites, which together improve the CO2 adsorption performance of NSPC. The novel NSPC displays amazing CO2 adsorption characteristics, and the practical, affordable synthetic approach exhibits significant potential to produce highly effective CO2 adsorbents on a broad scale.