Finely regulated polyamide membranes with rapid water transport for low-pressure precise nanofiltration

Abstract

Low-pressure nanofiltration (NF) has evinced huge application prospects for ion/molecule separation. However, current polyamide-based membranes made by highly reactive monomers offer less control in precisely tuning of their pore apertures, leading to a permeability-selectivity trade-off limit. Herein, the usage of amino-piperidine (AP, 4-aminopiperidine: 4AP; 3-aminoapiperidine: 3AP) is proposed as new building block that interfacially polymerizes with trimesoyl chlorides (TMC) onto a nanofibrous hydrogel to fabricate high-performance thin film composite (TFC) membranes. The resultant amino-piperidine thin film composite (AP-TFC) membranes with nodular and bubble-like surface have high hydrophilicity, electronegativity, and moderate crosslinking degree. Introducing an alkane bond length based on the piperidine structure allows to finely augment the free-volume elements of polyamide-based membranes, combined with varying the monomer concentrations. Furthermore, the 4AP-TFC membranes showed an excellent water permeability of 35.0 L m−2 h−1 bar−1 with Na2SO4 rejection above 98.5% when the 4AP concentration was 0.05 w/v%. The 4AP-TFC membrane was also found having a superior sieving capability for antibiotics, attributed to the synergy of size exclusion by well-defined ultra-microporous structure (<0.7 nm) and electrostatic repulsion due to the abundance of surface negative charges. This work provides the guideline of using AP molecules for the fabrication of high-crosslinked TFC membranes with potential applications in low-pressure NF, organic solvent NF, and related water purification.