Organosilica bis(triethoxysilyl)ethane (BTESE) membranes for gas permeation (GS) and reverse osmosis (RO): The effect of preparation conditions on structure, and the correlation between gas and liquid permeation properties

Abstract

The aim of this work was to study how the structural and permeation properties of BTESE membranes were affected by the simultaneous influences of water ratios (WRs) in sol preparation, defined as (H2O)/ bis(triethoxysilyl)ethane (BTESE), ranging from 3 to 240, and the firing atmosphere (under N2 and/or air, firing temperature 100–300°C) for gas permeation (GS) and reverse osmosis (RO) applications. The thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy, and N2 adsorption results revealed that the ethoxide groups in the pore networks of BTESE membranes were almost completely hydrolyzed and the silica networks became dense when the WR was increased from 3 to 240 regardless the firing environment. Based on the FTIR, most of the organic peaks for samples fired under N2 were more intense than the samples fired under air. Hence, the samples fired under N2 were more hydrophobic than the samples fired under air, as proven by the contact angle and H2O adsorption. This demonstrates that the firing of BTESE membranes under N2 slowed down the decomposition of organic bonds in the sample, and made the structures within the networks more intense and rigid. In terms of separation performance, the permeance of gases and H2O was clearly dependent on the WR. Increasing the WR decreased the permeance of both gases and H2O via the pore network of BTESE membranes. On the other hand, the firing environments also affected the permeance of gases and H2O. BTESE membranes fired under air exhibited a higher permeance of gases and H2O. In addition, we also investigated the relationship between gas and liquid permeance correlation using He gas as the predictor of water permeance. Increasing the He permeance resulted in increases in water permeance. Based on these results, it was suggested that the WR was a primary factor in controlling the pore size and solute rejections, and the firing environments played a primary role in deciding the hydrophilicity and hydrophobicity of membrane surfaces and pore networks during the fabrication of BTESE membranes.