Preparation of N and S Codoped Ultramicroporous Carbon Materials with a High CO₂ Adsorption Capacity

The environmental problems caused by excessive CO₂ emissions have made the development of adsorbent materials for capturing CO₂ an important topic. N-doped porous carbon materials are attractive for CO₂ adsorption because of their large specific surface area, porous structure, and multiple active sites. S and N are known to work well together as codopants, but the effects of S on N and the synergistic effects of S and N on carbon materials need to be clarified. In this study, N and S codoped porous carbon samples with an ultramicroporous structure were prepared by using lignin as the carbon source and thiourea as the sulfur source. The prepared samples had a specific surface area of up to 1723 m²/g and N and S contents of up to 1.60 at % and 0.23 at %, respectively. In tests, the best-performing sample had a CO₂ adsorption capacity of 3.58 mmol/g at 298 K and 1 bar, which can be attributed to ultramicropores (<1 nm) making up 67.8% of the pore volume. S doping had the synergistic effect of increasing the pyrrole N content on the sample surface, which increased the CO₂ adsorption capacity. The present study provides insights into using N and S codoping to develop high-efficiency carbon-based adsorbents for CO₂ capture.