No abstract

Mesoporous silica membranes, prepared by surfactant-templating with a pore diameter of $4 nm on an alumina support, are modified by atomic layer deposition (ALD) of aluminum oxide. ALD of aluminum oxide is achieved using trimethyl aluminum (TMA) and water as reactants. Membranes modified up to 50 ALD reaction cycles are characterized periodically during progressive reaction cycles to provide details of the pore modification process. A decrease in light gas permeance, pore size distribution shift to lower pore sizes, and a decrease in porosity provide evidence for pore-size reduction through ALD. Further analysis of the data indicates that the ALD reaction favors larger pores and defects, and becomes less efficient as the pore size decreases.

Atomic layer deposition has been used as a tool to modify mesoporous silica membranes. SiO2 has been deposited within mesoporous silica membranes using SiCl4 and H2O catalyzed with pyridine. Pore size reduction was self-limited and selectively reduced defective pores. Covalent attachment of silanes was also demonstrated by ALD. Both amino and alkyl groups were attached to mesoporous silica membranes. ALD is very effective for both pore size reduction and surface modification, yet is limited by the quality of the support material. ALD is a promising technique for membrane synthesis.

We report the synthesis and characterization of a selective nitric oxide (NO) adsorbent based on the covalent binding of cobalt(II) phthalocyanine tetrasulfonic acid (CoPcS) onto imidazole-functionalized mesoporous silica gel beads. The equilibrium data indicated that the adsorption of NO was highly favorable, approaching irreversible adsorption. The breakthrough curves for NO were modeled assuming irreversible adsorption and resulted in pore diffusivities through the packed bed of 0.1-0.3 cm 2 • s -1 . Adsorption experiments of NO in the presence of nitrogen, water vapor, and ammonia indicated that the adsorption was selective for NO.