Efficient CO2 removal enabled by N, S co-doped hierarchical porous carbon derived from sustainable lignin

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Biomass-derived heteroatoms-doped hierarchical porous carbon materials are highly regarded as promising CO2 adsorbents. However, these materials cannot simultaneously exhibit advanced porosity, high yield, and high heteroatom content. Herein, a series of N, S co-doped hierarchical porous carbons with advanced porosity (narrow micropore: 0.37–0.42 cm3/g), high heteroatom content (N content: 8.54 at% and 8.87 wt% and S content: 0.86 at% and 1.73 wt%) and remarkable yield (57.12–69.13 wt%) was produced using lignin as the raw material via a synergistic strategy involving melamine modification and CuCl2 activation. Notably, melamine modification not only introduced mesopores, but also promoted the effect of CuCl2 activation to generate additional micropores. Importantly, the advanced porosity required a low dosage of CuCl2. The optimized adsorbent (NHPC-850) exhibits outstanding CO2 adsorption capacity (6.87 mmol/g at 273 K and 100 kPa, 3.57 mmol/g at 303 K and 100 kPa), a moderately high heat of adsorption (34.7 kJ/mol), and an extraordinary CO2/N2 selectivity (132 at 273 K/81 at 303 K). These excellent properties are attributed to the well-developed micropores and suitable mesopores of carbon materials, as well as rich nitrogen and sulfur functionality in the carbon structure. Collectively, this work offers new insights into a simple and easy-to-scale strategy for the preparation of biomass-derived N, S co-doped hierarchical porous carbon.