Abstract
The adsorption of carbon dioxide on mesoporous silicas was studied near the critical temperature (Tc) of CO2, i.e. 304.2 K. The critical temperature in the mesopores at which the first-order phase transition (capillary condensation) was observed (Tcp) was estimated from the inverse slope of the adsorption isotherms and the behaviour of the adsorption isotherms per unit surface area. The values of Tcp for CO2 in mesopores whose radii, rp, were 3.02 and 2.14 nm were higher than those estimated using a slab model in which the adsorbing parts of layer were clearly separated from the non-adsorbing regions. The differential heat of adsorption decreased with increasing pore size of the mesoporous adsorbent. This result also suggested a deviation from the slab model.