Ultrathin Highly Porous Molecular-Sieve Silica Membranes Developed by a Facile Process Using Atmospheric-Pressure Plasma Modification

Microporous silica membranes are promising candidates for energy-efficient chemical separation processes. Herein, we aimed to address the permeance-selectivity tradeoff inherent in conventional silica membranes by applying plasma surface modification to pendant-type silica membranes. We focused on the bulkiness of pendant groups and employed phenyl-functionalized silica membranes. The modification enabled precise control over the pore structure and hydrophilicity within a thickness of less than 20 nm, attributed to the decomposition of bulky phenyl groups performing like nano templates, resulting in the formation of Si–OH groups and Si–O–Si cross-links. Consequently, the plasma-modified membrane exhibited a high H₂O permeance of 5.6 × 10^–6 mol m^–2 s^–1 Pa^–1 and H₂O/EtOH permeance ratio of 5300 in pervaporation dehydration, overcoming the tradeoff. A novel strategy for producing highly porous ultrathin silica membranes by a facile process employing atmospheric-pressure plasma surface modification is proposed.