SYNTHESIS AND CHARACTERIZATION OF MESOPOROUS SILICA MEMBRANES MODIFIED BY ATOMIC AND MOLECULAR LAYER DEPOSITION

                Inorganic membranes offer a means for chemical separations in a variety of applications including chemical processing, drug delivery systems, battery separators and fuel cells.  There is currently a “pore size gap” in silica membranes between 1-2 nanometers. Synthesizing membranes with a fine control of the pore size and distribution within that gap is a significant challenge.  This thesis reports our findings on using atomic and molecular layer deposition as new synthesis approaches to controlling pore size and chemical functionality of silica membranes.  Silica membranes were synthesized with pore diameters ~4 nanometers and were modified using atomic layer deposition and molecular layer deposition.   Atomic layer deposition (ALD) is a method to grow layers of atoms using alternating cycles of reactants, in our case alumina.  Molecular layer deposition (MLD) uses organic molecules to grow single layers of molecules per cycle creating a coating of inorganic-organic hybrid material inside the pores.

It was determined that the growth rate of atomic layer deposition of alumina within silica membranes was not linear, with a higher growth rate during the first 7 cycles and a lower rate afterwards.  Alumina ALD modification favored the larger pores increasing the separation factor of light gases.  In the MLD study, higher growth rates were observed when compared to ALD and the separation factor of light gases increased to a higher value as well. Analysis of several light gases suggested that a pore size reduction occurred.