The potential of hybrid organic-inorganic membranes for separating organic molecules from air, based on solubility selective mechanism, was evaluated. Alumina and titana membranes with average pore size near 4 nm were surface modified using trimethoxysilane fluorinated coupling reagent. The permeabilities to helium, nitrogen, methane, ethane, propane, butane and carbon dioxide were evaluated at feed pressures lying between (1.5 x 10(5) and 3.5 x 10(5) Pa) 1.5 and 3.5 bar and permeate outlet near 1 x 105 Pa (I bar). The permeabilities of the grafted membranes generally decreased by about two to three orders of magnitude compared with the untreated membranes. The CO2/N-2 permselectivity increased significantly in the case of the TiO2 grafted membrane. The membranes performances were compared and the TiO2 grafted membrane exhibits higher permselectivity and permeability, so that. it is a good candidate for CO2 to N-2 separation and CO2 to hydrocarbon separation. (c) 2005 Elsevier B.V. All rights reserved.