An equilibrium model capable of describing CO2 adsorption isotherms on amine-grafted mesoporous silica using a semi-empirical method was developed. The proposed model is based on the assumption that adsorption of CO2 occurs via two independent mechanisms: (i) chemical adsorption on the amine-functional groups, and (ii) physisorption on the surface of the adsorbent. The CO2 adsorption isotherms on triamine-graftecl pore-expanded MCM-41 silica were measured at different temperatures and used to develop the proposed model. The equilibrium model was capable of describing CO2 adsorption over a wide range of pressure, from 0.001 to 20 bar. Furthermore, when applied in a temperature-dependent form, it fitted experimental data at different temperatures between 25 and 55 degrees C. The adequacy of the model was reflected by the low values of the normalized standard deviations (<8%) obtained at all temperatures. The model was also successfully used to fit experimental CO2 isotherms of a triamine-grafted mesoporous silica with lower amine content and five varieties of monoamine-grafted SBA-15, as well as experimental data for H2S adsorption at 25, 35 and 50 degrees C. Moreover, the heat of CO2 and H2S adsorption calculated using the temperature-dependent parameters of the proposed model was in excellent agreement with experimental data. (C) 2010 Elsevier B.V.. All rights reserved.