Realizing ultrathin silica membranes with straight-through channels for high-performance organic solvent nanofiltration (OSN)

In this study, a thin membrane with vertically aligned mesoporous silica nanochannels was modified with long silane group molecules (E-MSTF-LTA) supported on an anodic aluminum oxide (AAO) for organic solvent nanofiltration (OSN). The ultrathin thickness, low tortuosity, ordered vertical channels and super-organophilic surface of E-MSTF-LTA endow it with an ultrahigh ethanol permeance (110 LMH/bar) over current state-of-the-art OSN membranes and a high acetone permeance of 360 LMH/bar. Furthermore, a 99% rejection of Evans blue (EB) was demonstrated, and a cut-off of approximately 660 Da was achieved. Besides, the modified Hagen-Poiseuille (HP) equation was applied to evaluate the theoretical permeance, which is consistent with the experimental results. To explore in depth the underlying principle behind the OSN performance of the vertically aligned E-MSTF-LTA membrane, the parameters, including the solvent viscosity, total Hansen solubility, solvent diameter, and solvent polarity were introduced to evaluate their influence on the permeance, while for solute transport behavior, the impact of the size exclusion effect on the solute rejection rate was examined. The results show that the viscosity is the critical factor for determining the solvent permeation, while the size exclusion effect dominates solute rejection. These findings open up a way to design next-generation vertically aligned OSN membranes and shed light on the OSN performance, both empirically and theoretically, using this system.