Pore Structure Controllability and CO₂Permeation Properties of Silica-Derived Membranes with a Dual-Network Structure

We proposed a novel method for designing CO₂permselective organosilica/polymer membranes with a dual-network structure composed of silica (first) and alkylamine-based (second) networks to control molecular sieving and CO₂adsorption properties in the membrane. Organosilica/polymer membranes were fabricated using 1,2-bis(triethoxysilyl)ethane (BTESE) or 1,2-bis(triethoxyailyl)acetylene (BTESA) as the first network, with polyethylenimine (PEI) as the second network via the sol-gel process. CO₂adsorption measurements of BTESE/PEI films were conducted viain situFourier transform infrared to evaluate the effects that different types of acid catalysts exert on CO₂adsorption properties. The results showed that only BTESE/PEI films prepared with a catalyst of acetic acid (HAc) display impressive chemical reactions between CO₂and amine groups, whereas the use of HCl may deactivate the amine groups. We found that the gas permeation properties of organosilica/PEI membranes were greatly dependent on the Si-precursor. Almost no selectivity could be confirmed for BTESA/PEI membranes, although pure BTESA membranes did show molecular sieving properties. However, BTESE/PEI membranes showed improved separation performance compared with that of pure BTESE membranes due to a reduction in the free volume (BTESE: H₂/CH₄selectivity < 100, BTESE/PEI: H₂/CH₄> 100). Moreover, the pore size of BTESE/PEI membranes could be controlled via the BTESE/PEI ratio. In conclusion, we successfully designed a dual-network structure with a controlled pore size via changes made to the Si-precursor and/or to the Si-precursor/PEI mixing ratio.