A critical challenge in developing engineered materials for low-energy-cost carbon capture and storage applications is to fundamentally understand adsorption, particularly when the materials exhibit hysteretic sorption behavior. We used first-principles calculations and combined with experiments to explore CO2 sorption in a nanoporous solid: cryptomelane-type manganese dioxide (OMS-2). Cations present in this material to not only stabilize its porous structure but also tailor CO2-pore interaction. The concentration, type and charge of cations have significant effects on CO2 adsorption, diffusion and hysteresis behavior. OMS-2 with lower-charge cation, e.g. K+ (Cryptomelane), exhibits less hysteresis than OMS-2 with higher-charge cation, e.g. Ba2+ (Hollandite). (C) 2013 Elsevier B.V. All rights reserved.