Innovative integration of porous materials and membranes: Achieving optimized pore orientation for enhanced performance

Abstract

Incorporating inorganic porous materials into polymer membranes presents a promising strategy to rectify their inherent imperfections. Nonetheless, achieving peak efficiency necessitates pores oriented perpendicular to the membrane surface, a feat that remains challenging due to orientation control complexities. In this study, a novel synthesis approach for two-dimensional (2D) mesoporous silica nanoparticles (MSN) featuring high aspect ratios and vertical pore channels is presented. These channels, oriented perpendicular to the membrane surface, optimize water permeability. This unique orientation is meticulously achieved via cetyltrimethylammonium bromide (CTAB) acting as a surfactant at the nexus of polar and non-polar fluids, guaranteeing interface evenness. Intriguingly, the resultant mesoporous compound harbors both micro and mesopores—a phenomenon attributed to surfactant non-polar segment expansion within non-polar solvents or the distinct U-shaped interface upon contact with hydrophilic mesoporous entities. After depositing a tannic acid (TA) coating on a polyvinylidene fluoride (PVDF) base membrane, 2D MSN was fixed on the membrane surface using polyethyleneimine (PEI) as a linker through strong hydrogen bonding. Thanks to the asymmetric structure of the mesoporous separation layer combining micro and mesopores, the perpendicular pore channels with superhydrophilic features, water can permeate through the separation membrane with the shortest distance and lowest resistance, achieving an ultra-high pure water permeation volume of 394.5 L−1h−1bar−1. The uniform pore channels of 2D MSN show a rejection rate of over 97% for large molecular dyes such as Evans blue (EB), Congo red (CR), and Rose Bengal sodium (RB). This work not only advances the synthesis of two-dimensional materials with vertical pore channels but also underscores their potential in membrane separation applications.