Sub-nanometer scale tailoring of the microstructures of composite organosilica membranes for efficient pervaporation of toluene/n-heptane mixtures

Amorphous organosilica-based membranes are of enormous potential for pervaporation separation of organic mixtures, however, engineering organosilica membranes with the on-demand pore size and functionality for precise molecular sieving still remains a challenge. Herein, as a proof-of-concept, we proposed a facile and novel co-condensation strategy by pairing the biphenyl-bridged organosilica precursor (BTESBP) with another organosilica precursor (PhTES) equipped with a phenyl pendant group for efficient pervaporation of aromatic/ aliphatic mixtures. It was demonstrated that the strong aromatic pi-pi interactions between BTESBP and PhTES as well as the steric hindrance effect of PhTES allowed the tailoring of membrane pore size at the sub-nano scale, and enhanced the accessibility of biphenyl groups to aromatic hydrocarbons. At the optimal BTESBP/PhTES mass ratio of 98/2, the resulting BTESBP/PhTES composite organosilica membrane achieved superior toluene/nheptane pervaporation separation performance with a total flux surpassing 1 kg m(-2) h(-1) and a separation factor of 8-10 for a 50 wt% toluene/n-heptane feed mixture. Hopefully, this study can stimulate the rethinking of the design principles for composite organosilica membranes and the subsequent development of advanced membranes for energy-efficient pervaporation of organic mixtures.