Converting polar silicon surfaces of ordered mesoporous materials to non-polar carbon surfaces for enhanced carbon dioxide capture

Abstract

The ordered mesoporous carbon-silica composite samples were synthesized by the unremoved template agent (P123) or together with additional sucrose as carbon sources. The effects of sulfuric acid and sucrose added on the properties of the synthesized materials were discussed. Ordered mesoporous structures of the synthesized materials were examined by XRD, TEM, and the 77 ​K N2 adsorption-desorption isotherms characterization. Compared to the silicon SBA-15 sample, the pore walls of carbon-silica composite materials were covered with carbon film, so their pore sizes became smaller and their surface properties were changed from polarity to hydrophobicity. The capturing CO2 performances on two dry/wet carbon-silica samples (SC-1.5, SCC-2) were collected at 275 ​K. Whether or not pre-adsorbed water, the CO2 adsorption capacities of the carbon-silica composite samples were higher than that of SBA-15. For the wet SC-1.5 sample with the mass ratio water/dry sample (Rw) of 3, the capturing CO2 capacity was 32 ​mmol/g at the pressure of 3 ​MPa. The H2O/CO2 mole ratios of the wet SC materials under different Rw were all lower than the theoretical value (5.75). The mechanisms of capturing CO2 on wet carbon-silica composite materials were multiple, which included CO2 dissolution in water, CO2 adsorption in pore space, and CO2 gas hydrate formation. The suddenly increasing CO2 adsorption capacity on the wet SC-1.5 material was mainly due to the formation of CO2 gas hydrates in its pore spaces.