Diazotized polyamide membranes on commercial polyethylene textile with simultaneously improved water permeance, salt rejections and anti-fouling

Abstract

Membrane desalination is the most critical strategy for global water scarcity. Anti-fouling and higher water/salt perm-selectivity are consistent goals for desalination membranes. However, the trade-off between the water permeance and salt rejection, and fouling remaining challenges for polyamide (PA) thin–film composite (TFC) desalination membranes. Here, we apply ultrathin (~5 and ~9 μm) polyethylene (PE) textile with highly porous and inter-connected pore structures to constitute the PA–TFC desalination membranes. A series of PE–supported PA–TFC membranes were prepared by interfacial polymerization (IP) reaction, and obtained TFCx (X represents the thickness of PE textile) membranes showed promising water flux as well as high NaCl rejection under reverse osmosis (RO) and forward osmosis (FO) desalination processes. Diazotization utilizes the nucleophilic aryl substitution reaction between the diazonium salt and residual aromatic to covalently graft a PA layer. The resulting TFCx–N membranes after diazotization exhibited simultaneously improved water permeance and salt rejections as well as anti-fouling performances, e.g., the resulting TFC5–N membrane showed water permeability of 5.95 L m−2 h−1 bar−1 at 65 °C under RO, and the excellent rejection of salts (NaCl >97.8 % and MgSO4 > 98.9 %). Two-dimensional (2D) grazing incidence wide-angle X-ray scattering (GIWAXS) demonstrated the crystallization behavior of PA layer by diazotization. The 2D GIWAXS results suggested that the parallel “π–π” stacking of PA molecular packing motifs was destroyed after diazotization, and the perpendicular “T-shaped” configuration might be associated with optimal desalination performance of the TFC5–N membrane.