Sulfur-Nitrogen Codoped Graphite Slit-Pore for Enhancing Selective Carbon Dioxide Adsorption: Insights from Molecular Simulations

Using Grand Canonical Monte Carlo calculations, sulfur and nitrogen codoped (S/N-) graphite slit-pores with different defects (Divacancy 5-8-5, NS-1, NS-2, StoneWales (SW) 5577) are constructed to study their selective CO2 adsorption from CO2/H-2, CO2/N-2, CO2/CH4 and CO2/H2O mixtures. Among all the defective S/N-graphite slit-pores, it is found that the doped sites of S and N atoms affect slightly on CO2 uptake of graphite slit-pore. More importantly, the increasing ratio of S/N enhances the selective CO2 adsorption. For example, at 300 K and 1 bar, the full N-graphite slit-pore with SW 5577 has a CO2 uptake of 79.77 mmol/mol with good CO2/H-2 selectivity (similar to 356) whereas full S-graphite slit-pore with SW 5577 possesses a considerable CO2 uptake of 104.66 mmol/mol with excellent CO2/H-2 selectivity (similar to 526). Furthermore, density functional theory calculations indicate this defective S/N-graphite slit-pore with higher ratio of S/N interacts more strongly with CO2 molecules compared with other gases, which demonstrates that S doping is a better choice than S/N codoping for impressive selective CO2 capture.