Surface chemical modulation of nitrogen-doped microporous carbon for efficient removal of H2S and CO2: The effect of nitrogen functionality

Abstract

The removal of hydrogen sulfide (H₂S) and carbon dioxide (CO₂) is of paramount importance for mitigating environmental pollution. However, due to the difficulty in accurately controlling the surface chemistry, the performance of carbon materials in the simultaneous removal of H₂S and CO₂ remains relatively limited. Herein, nitrogen-doped microporous carbon with well-developed pore structure was prepared through a combination of hydrothermal synthesis and molten salt method. The impact of nitrogen-doped surface chemistry on the removal performance for H₂S and CO₂ at room temperature was primarily studied. Owing to its abundant micropores and ultramicropores, the material possesses sufficient basic sites that can effectively remove CO₂. Pyrrolic nitrogen serves as the primary basic site during CO₂ adsorption, which exhibits an excellent CO₂ adsorption capacity of 136.97 mg CO₂/g. The high nitrogen content provides a strongly alkaline environment conducive to the dissociation of H₂S on the carbon surface, with pyrrolic nitrogen being the main basic site during the catalytic oxidation of H₂S. The large pore volume offers sufficient storage space for desulfurization products, enabling a sulfur capacity of 2.56 g H₂S/g. DFT calculations reveal that pyrrolic nitrogen undergoes the largest change in charge before and after the adsorption of CO₂ and H₂S, due to its strong adsorption effect on both gases. In the presence of both CO₂ and H₂S, competition for active sites leads to a decline in the removal performance for both gases. This work holds significant implications for the design of materials for the simultaneous removal of CO₂ and H₂S.