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

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.