Functionalization of silica membranes is important for enhancing surface interactions with specific chemicals in order to enhance separations. It is important to develop synthesis strategies that allow control over the density and the surface chemistry of the functional group in order to tailor the membrane separation properties. In this paper we investigate the ability of amino functionalization to enhance CO2 transport in silica membranes. Specifically, we examine three synthesis techniques for functionalizing silica membranes with amino groups that result in different surface chemistries of the silica membranes. Silica membranes are amino-functionalized by atomic layer deposition (ALD) with aminopropyldimethylethoxysilane (APDMES), ethylenediamine (EDA)-assisted APDMES ALD, and direct attachment of aminopropyltriethoxysilane (APTES) from the liquid phase. Three different reaction schemes are presented and verified by using Fourier-transform infrared (FTIR) spectroscopy. The FTIR measurements were performed on silica powders that were processed using the same reaction conditions as the membranes used in this study. The differences in reaction schemes are correlated with changes in the CO2 facilitation characteristics. It is found that high loadings of amino groups, in which interaction with the silica surface is minimized, promote the highest CO2 transport.
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