Amine Functionalization of Microsized and Nanosized Mesoporous Carbons for Carbon Dioxide Capture

Carbonaceous nanomaterials with uniform pore size are potential solid sorbents in various industrial applications, such as gas purification and water treatment, because of their easily tunable pore diameter and morphology. However, the carbon-based sorbents are greatly limited in CO₂ capture, because of their weak interaction with CO₂ (physical adsorption in nature). This work reports the amino functionalization of microsized and nanosized mesoporous carbons for CO₂ capture. Two strategies, i.e., physical impregnation with branched polyethylenimine (PEI) and chemical grafting of ethylenediamine, are used to functionalize mesoporous carbon microparticles (MCMs) with a particle size of 100-200 μm. The amine-grafted MCMs (NH₂-MCMs) show little advantage over PEI-impregnated MCMs (PEI/MCMs) in CO₂ adsorption capacities, because of their similar surface functional groups and textural properties. In addition, mesoporous carbon nanospheres (MCNs) with a sphere size of 850-1000 nm are prepared by a silica-assisted self-assembly method for comparison with MCMs. The PEI-impregnated MCNs (PEI/MCNs) have higher CO₂ adsorption capacities and amine efficiencies than PEI/MCMs at the same PEI loading, indicating a more efficient utilization of the incorporated PEI in the nanosized carbon spheres. The best-performing PEI/MCNs adsorbent shows a CO₂ capacity of 1.97 mmol-CO₂ g^-1 at 75 °C, which is more than three times that of PEI/MCMs.