The properties of inorganic membranes are dependent on the surface chemistry of the material, which in turn are affected by parameters such as temperature, pH, and chemisorption of molecules. For both silica and gamma-alumina membranes, a significant reduction in water hydraulic permeability was observed after heat treatment or exposure to organic solvents. For silica membranes, the water permeability reduction due to heating at 140 degrees C has been attributed to the removal of physically adsorbed water, which exposes hydrophobic surface patches covered by isolated hydroxyl groups, In the case of gamma-alumina membranes strong adsorption of a wide range of organic compounds can result in significant permeability loss.