The removal of excess CO2 from the atmosphere is expected to play a major role in the mitigation of global warming. Solid-state adsorbents, consisting of CO2-binding functionalities on porous supports, can provide high CO2 capture capacities with low energy requirements. In this contribution, we report on the vapor-phase functionalization of porous carbon fibers with amine functionalities. Functionalization occurs either via direct exposure to cyclic azasilane molecules (2,2-dimethoxy-1,6-diaza-2-silacyclooctane) or by the atomic layer deposition of Al2O3 followed by exposure to azasilane. XPS analysis and SEM/energy-dispersive x-ray spectroscopy (EDX) measurements confirmed Al2O3 deposition and amine functionalization. Yet, the two different functionalization approaches led to different amine loadings and distinct differences in porosity upon functionalization, which affected CO2 capture. Combining Al2O3 and amine functionalization resulted in fast CO2 sorption with superior capturing efficiency. In contrast, direct functionalization resulted in strong reduction of the surface area of the porous support and limited gas exchange. We attribute the superior capture efficiency to the porosity level achieved when combining Al2O3 and amine functionalization demonstrating that this approach might be valuable for compact high-throughput direct air, CO2 capture systems.
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