Micropore structure stabilization in organosilica membranes by gaseous catalyst post-treatment

A post-treatment involving repeated exposure to gaseous HCl alternated with heating is demonstrated to strongly accelerate the recently reported structural evolution in organically bridged silica networks. Films, powders and membranes derived from 1,2-bis(triethoxysilyl)ethane were exposed to in-situ synthesized HCl gas, alternated with heat treatments at 150-300 °C in air or N2. The film thickness, network condensation, chemical integrity and micropore structure were monitored with X-ray reflectivity, 29Si direct excitation magic angle spinning nuclear magnetic resonance, Fourier-transform infrared spectroscopy and gas permeation. Treatment with HCl was found to predominantly catalyze hydrolysis, enabling network optimization via iterative bond breakage and reformation. Network shrinkage, widening or opening of the smallest pores and densification of the overall pore structure were accelerated while the ethylene bridges remained intact. The achieved acceleration of material evolution makes iterative hydrolysis and condensation a promising approach for increasing the long-term micropore stability of molecular sieving membranes.