Sulfur-containing functional groups promoted CO2 adsorption

https://doi.org/10.1016/j.ccst.2022.100059

“Compared to nitrogen-containing functional groups, sulfur-containing functional groups have yet to be investigated in relation to CO₂ adsorption (Saha and Kienbaum, 2019). Some researchers suggest that the presence of sulfur-containing functional groups such as sulphonic acid, sulphoxide, sulphone and thiophene on biochar can increase the alkalinity and surface polarity of biochar, and therefore enhancing the adsorption of CO₂ through acid-base interactions and polar interactions (Saha et al., 2017; Seema et al., 2014). Several researchers have analyzed the adsorption energy as supporting evidence for the effect of sulfur functionality in CO₂ adsorption. Xia et al. (Xia et al., 2012). calculated that the CO₂ adsorption energy (Qst) of carbon with sulfur-containing functional groups was as high as 59 kJ/mol, indicating a strong interaction between CO₂ molecules and S-doped carbon pore walls. Li et al. (Li et al., 2017). used calculations using density-functional theory (DFT) to demonstrate that S-doping can increase the adsorption energy between CO₂ molecules and the S-graphene surface.

In recent years, some investigations have been conducted on nitrogen and sulfur co-doped biochar materials for CO₂ capture. The co-doped biochar adsorbents all exhibit good CO₂ adsorption properties, fast CO₂ adsorption kinetics, and moderate heat of adsorption (Zhao et al., 2015; Lu et al., 2021; Ma et al., 2022; Shi et al., 2019; Shao et al., 2022), but not much research has been done on the adsorption mechanisms of nitrogen and sulfur functional groups. The current study is expected to provide new insights into the mechanism of CO₂ adsorption on heteroatom-doped biochar.”