Polybenzoxazine-based monodisperse carbon spheres with low-thermal shrinkage and their CO2 adsorption properties

Abstract

We describe the synthesis of polybenzoxazine-based spheres that can be carbonized with little shrinkage to produce monodisperse carbon spheres with abundant porosity. The porous structure of the carbon spheres was analyzed by nitrogen sorption isotherms. Elemental analysis, infrared spectroscopy and ¹H → ¹³C CP/MAS NMR analysis were carried to characterize the surface chemistry of the spheres. The porous carbon spheres contain intrinsic nitrogen-containing groups that make them more useful for CO₂ adsorption. The CO₂ adsorption capacity can reach 11.03 mmol g⁻¹ (i.e. 485 mg g⁻¹) at −50 °C and ∼1 bar, which is highly desirable for the CO₂ separation from natural gas feeds during the cryogenic process to produce liquefied natural gas. Moreover, the prepared carbon spheres show the highest adsorption capacity for CO₂ per cm³ micropore volume, when compared with recently reported carbon adsorbents with high CO₂ capture capacities at low temperature. Due to the uniform size and low thermal shrinkage during production, the carbon spheres were also used as models to investigate the influence of porous structure and surface chemistry on CO₂ adsorption behavior. The porosity plays an essential role in achieving high CO₂ adsorption capacity at ambient pressure, while the nitrogen content of the carbon adsorbent is a booster for CO₂ adsorption capacity at low pressures. This finding may be beneficial to design sorbents for the separation of dilute CO₂-containing gas streams in practical applications.