Novel thin-film composite membrane with ultrathin surface mineralization layer engineered by electrostatic attraction induced In-situ assembling process for high-performance nanofiltration

An ultrathin mineralization layer, comprising inorganic silica nanoparticles, was facilely in-situ engineered onto an organic polyamide (PA)-based membrane substrate via electrostatic attraction induced surface mineralization for nanofiltration. Based on transport behavior, the pre-infiltrated tetraethoxysilane monomers can act as spacers to break up the tightly structured PA-based matrix during the in-situ mineralization process, endowing the resultant thin-film composite (TFC) membrane with enlarged internal free volumes (voids) for the rapid transportation of water molecules. More importantly, the deposited mineralization layer further enriched the PA membrane with enhanced hydrophilicity and/or internal polarity with more accessible sites for water molecules to penetrate more easily into the membrane matrix. Consequently, the newly developed ultrafine silica nanoparticle-decorated PA-based (SiO2-d-PA) TFC membranes exhibited a high water permeance of 9.47 L m−2 h−1 bar−1 and a compelling rejection ratio of 95.2% toward Na2SO4, thereby generating an over two-fold increase in water permeability without sacrificing membrane selectivity. The surface mineralization layer endows the SiO2-d-PA TFC membrane with effective fouling-resistant/fouling-releasing property for comprehensive Ca2+-based suspensions containing bovine serum albumin, humic acid, and sodium alginate, whereby a full recovery of the permeating flux can be attained after three filtration-cleaning cycles. Simultaneously, the robust durability of the mineralization layer firmly anchored onto the PA-based membrane substrate can be obtained under harsh operating conditions (cross-flow, high-pressure, and continuous long-term filtration) owing to the electrostatic attraction incorporated with H-bond interaction. Overall, this study provides an insightful guideline for the development of novel inorganic/organic membranes with high permselectivity and low fouling propensity for high-performance nanofiltration. © 2020