Modification of zeolite or molecular sieve membranes using atomic layer controlled chemical vapor deposition

A process for modifying selective permeance of a crystalline membrane with hydroxyl groups (OH) on its surface, comprising:

• exposing the membrane to a reaction gas molecule having the formula M(Z.sub.m L.sub.n), where M is a metal atom coordinated to ligand group Z.sub.m L.sub.n, wherein said membrane has the formula Y-OII*, wherein Y is a substrate atom and OH* is a surface hydroxyl group, and wherein said reaction gas molecule M(Z.sub.m L.sub.n) has sufficient volatility and reactivity to react with said membrane surface hydroxyl group, and allowing a solid/vapor phase chemical reaction to proceed generally as follows:
• Y--OH*+M(Z.sub.m L.sub.n).fwdarw.Y--O--M(Z.sub.m L.sub.n)+ZH.uparw.(1)
• where Y--O--M(Z.sub.m-1 L.sub.n)is a bonded coordinated group that results from reaction (1), M(Z.sub.m-1 L.sub.n) coordinated is a resulting group comprising the metal atom (M) and ligand group Z.sub.m-1 L.sub.n, wherein Z.sub.m-1 L.sub.n is capable of being hydrolyzed by water, and ZH.uparw. is a gaseous by-product of the reaction (1);
• and
• exposing the surface of the membrane and the bonded Y--O--M(Z.sub.m-1 L.sub.n) coordinated group that results from reaction (1) to water (H.sub.2 O) molecules to hydrolyze M(L) bonds according to a hydrolyzing reaction generally as follows:
• M(Z.sub.m-1 L.sub.n)*+H.sub.2 O.fwdarw.M--OH*+Z.sub.m-1 L.sub.n H.uparw.(3)
• where M(Z.sub.m-1 L.sub.n)* is the group on the membrane surface comprising the coordinated metal atom (M) and ligand group (Z.sub.m-1 L.sub.n), M--OH* is a resulting group comprising the metal atom M coordinated with a hydroxyl group (OH) formed on the surface of the membrane, and Z.sub.m-1 L.sub.n H.uparw. is a gaseous by-product of the hydrolyzing reaction (3), wherein a monomolecular layer of said M--OH* is deposited on the surface of said membrane.