Tailoring porosity in carbon spheres for fast carbon dioxide adsorption

Highly-porous carbon spheres were prepared by modified Stöber method combined with silica templating and CO₂ activation. Silica was delivered in the form of either colloids or tetraethyl orthosilicate and used to create porosity. Subsequently, CO₂ activation was used to develop microporosity. CO₂ activation was done either: (1) on carbon spheres, following silica etching or (2) on silica-carbon composites, before silica removal. Both methods delivered carbon materials with well-developed structures and, importantly, preserved spherical morphology. Still, activation of the silica-carbon composites with subsequent silica etching afforded carbons with better structural properties and CO₂ adsorption. Between materials prepared with silica colloids and TEOS-generated silica, the former showed more developed structures. The best material had specific surface area reaching 1500 m² g^-1 and total pore volume exceeding 1.2 cm³ g^-1 and showed CO₂ uptakes as high as 7.8 mmol g^-1 (0 °C, 1 bar) and 4.0 mmol g^-1 (23 °C, 1 bar). Mesoporosity improved mass transfer, which directly translated to faster CO₂ equilibration (30-40% on average). The proposed synthesis afforded carbons with high and fast CO₂ adsorption, which makes them good candidates for CO₂ sorption applications. Moreover, it was shown that both, microporosity and mesoporosity, are important in development of prospective CO₂ sorbents.