A new aminosilicate, sol-gel derived microporous inorganic membrane has been developed for enhanced CO2 separation in applications such as removal of metabolic CO2 from the breathing loop of the NASA extravehicular mobility unit (EMU), natural gas purification, or CO2 capture from coal-fired power plant emissions. This membrane consists of an inorganic, amorphous silica matrix of pore size 4-5 angstrom, containing randomly dispersed amine (-NH2) functional groups in order to enhance its CO, selectivity, due to preferential adsorption of CO2 in the membrane pore walls and simultaneous blocking of permeation of other gases (O-2, N-2 and CH4). It is found that the gas feed condition during permeation (partial pressure of CO2, relative humidity), post-synthetic treatments and aging, affect significantly the separation performance of the membranes. At this stage of development, with feeds of 1-20 vol.% CO2 and 0-40% relative humidity at 22 degrees C, the highest CO2:N-2 separation factor was in the range 100-200, while the CO2 permeance was in the range 0.1-1.5 cm(3) (STP)/(cm(2) min atm). The results suggest that controlling the membrane pore size and method of activation of amine groups are the most critical factors for improving the CO2-permselectivity of the membrane. (C) 2004 Elsevier B.V. All rights reserved.