Silica porous membranes synthesis and characterization

Abstract

Membranes can be made by various methods and are generally classified as either organic or inorganic. In recent years there has been a growing interest in the use of inorganic membranes for several industrial and laboratory applications. This is because they offer many advantages over commercial organic membranes, the most important of which are: steam sterilizability, resistance to organic solvents, longer lifetime, with standing cleaning by bleaching, and oxidizing agents. For applications in ultrafiltration UF and reverse osmosis RO, the sol–gel process provides the technique for producing thin ceramic porous layers with controllable porosity on a wide range of chemically resistant macroporous substrates. In this work, we have used two sol–gel procedures for obtaining inorganic membranes: polymerization of molecular units (PMU) and destabilization of colloidal solutions (DSC). The first (PMU) concerns polymeric oxide gels made in our case from metal alkoxide Si(OC2H5)4. Hydrolysis and polymerization reactions are very important for the properties of gel. The second process (DSC) is the destabilization of colloidal solution; we use peptization of hydrous metal oxide with an electrolyte. These colloidal solutions are then destabilized for instance by increasing the compounds concentration in the solution (by evaporation) thus gelation occurs. Thin membrane layer was deposited on a porous support. This is possible by infiltrating a low viscosity sol or by direct coating onto an ultrafiltration layer. Membranes produced using the two procedures were examined by X-ray diffraction, infrared spectroscopy, differential thermal analysis, nitrogen adsorption–desorption, and scanning electron spectroscopy. The control of sol–gel transition and thermal decomposition has allowed us the synthesis of silica membranes destined at separation, concentration, or purification of chemical species.