Tuning sol size to optimize organosilica membranes for gas separation

A series of organosilica sols are prepared by the polymeric sol–gel method using 1, 2-bis(triethoxysilyl)ethane (BTESE) as the precursor. Particle size distributions of the BTESE-derived sols are systematically investigated by carefully adjusting the synthesis parameters (i.e., water ratios, acid ratios and solvent ratios) in the sol process. In certain conditions, increasing the water ratio or the acid ratio tends to cause larger sol sizes and bimodal particle size distributions. However, higher solvent ratios lead to smaller sol sizes and unimodal particle size distributions. The organosilica membranes prepared from the optimized sols show excellent H₂ permeances (up to 4.2 × 10^{− 7} mol·m^{− 2}·s^{− 1}·Pa^{− 1}) and gas permselectitivies (H₂/CO₂ is 9.5, H₂/N₂ is 50 and H₂/CH₄ is 68). This study offers significant insights into the relationship between the sol synthesis parameters, sol sizes and membrane performance.