A new inexpensive inorganic-organic composite sorbent for CO2 capture was prepared by the immobilization of a branched polyethyleneimine (PEI) onto porosity-enhanced clays using the wet impregnation method. In the composite, a low cost and naturally abundant clays (e.g. kaolinite and montmorillonite) was used as the supporting material, which was pre-modified by acid- or alkaline-treatment to improve its textural properties, i.e. pore volume and surface area, for accommodating the CO2-philic PEI. Among the modified clays, the montmorillonite modified by 6 M HCl(Mon_HCl_6M) showed the highest porosity with the pore volume of 0.71 cm(3)/g from 0.16 cm(3)/g, and BET surface area of 253 m(2)/g from 72 m(2)/g. The cost of the Mon_HCl_6M was estimated as $0.14/kg, which was significantly lower than reported supporting materials for the amine-based sorbents for CO2 capture. At the optimal PEI loading of 50 wt% on the Mon_HCl_6M support, the CO2 sorption capacity reached 112 mg CO2/g-sorbent at 75 degrees C under dry condition, which can be further enhanced to 142 mg CO2/g-sorbent with the moisture addition (ca. 3 vol%) due to the change in the interaction mechanism between CO2 and amine in the presence of moisture. Moreover, the PEI/Mon_HCl_6M sorbent showed a good regenerability for 10 sorption-desorption cycles tested and a good thermal stability in the temperature range of CO2 sorption (75 degrees C) and desorption (100 degrees C). (C) 2013 Elsevier Ltd. All rights reserved.