Preparation chemistry of inorganic membranes

Membranes are thin films allowing for selective transport of mass species, such as gases, liquids, or ions. The major advantages of inorganic membranes as compared to polymeric membranes are their better thermal, chemical, and mechanical stability and higher permselectivity. The disadvantages are higher membrane costs and an increased difficulty toward making membrane modules with high packing densities. Inorganic membranes will find applications that require high permselectivity and good chemical and thermal stability beyond what can be offered by polymeric membranes. The most important properties of inorganic membranes include permeance and selectivity. These properties of microporous and mesoporous membranes are determined by the pore size, porosity, and membrane thickness. Chemistry plays a very important role in controlling these properties. Microporous amorphous silica membranes can be prepared by the acid catalyzed solegel method using an alkoxide precursor. The intercrystalline defects and zeolitic pores of crystalline zeolite membranes can be eliminated or narrowed by chemical vapor deposition through proper control of the surface chemistry of the zeolite framework. The membranes are very thick because synthesis chemistry gave large metal-organic framework crystals. Synthesis chemistry controls the pore size and structure of ordered mesoporous materials as well as orientation of the pore of the ordered mesoporous membranes.