Catalytic effect of trifluoroacetic acid on the CO2 transport properties of organic-inorganic hybrid silica membranes

Abstract

Developing silica membranes that are highly selective for CO2 has always been a challenge due to the small sizes of the pores and less amount of CO2 philic sites in a typical silica network structure. Herein, we describe the fabrication of silica (tetraethoxysilane) membranes functionalized with 3-aminopropyltriethoxysilyl (APTES) and trifluoroacetic acid (TFA). An interaction generated among primary (NH2) amines and TFA was identified, which was then also revealed by the reversible nature of CO2 adsorption/desorption — an opposite trend from observations when using another catalyst (HCl). The resultant TEOS-APTES (TFA) membranes demonstrated CO2 permeance of 3.8 × 10−7 mol m − 2 s − 1 Pa−1 and CO2/N2 selectivity of 35 at 50 ⁰C via the effect of surface diffusion. This is attributed to the increased microporosity and structural variations affected by TFA, which enhanced molecular sieving and controls the CO2-philic sites (-NHCOCF3) via interaction with amines. This novel approach would be effective for the energy-efficient fabrication of highly CO2-permeable membranes.

Keywords

• Amine-silica membranes
• Trifluoroacetic acid
• Amide formation
• CO2 separation