Tailoring high-performance polyester loose nanofiltration membrane for selective separation of salt/dyes: The equilibrium of condensation and hydrolysis

Polyester (PE) loose nanofiltration (LNF) membranes featuring outstanding water permeance and prepared from hydroxyl-containing monomers under alkali-activated conditions are ideal for dye/salt separations. However, condensation and hydrolysis of the PE membranes during alkali activation have rarely been investigated. Herein, sodium hydroxide (NaOH) was chosen to create alkaline conditions, and poly(vinyl alcohol) (PVA) and trimesoyl chloride were chosen to prepare PE LNF membranes. The condensations and hydrolyses of the PE films were tailored by adjusting the NaOH concentration. Stopped-flow mass spectrometry showed that the alkaline conditions affected the rate of interfacial polymerization. In addition, with lower alkaline concentrations, OH- preferably activated the PVA rather than increase its diffusion rate, thereby promoting membrane condensation. With higher alkaline concentrations, the OH- promoted hydrolysis of the membrane, causing damage to the PE network. Finally, the effects of different alkaline conditions on the morphological characteristics, surface characteristics, and dye desalination capacities of the membranes were comprehensively studied. The mechanisms for the role of alkaline conditions on the membrane condensation and hydrolysis equilibria were probed via molecular dynamics and density functional theory simulations. This work illustrates the significant potential of PVAbased membranes for resource recovery and provides a novel approach to the preparation of high-performance PE membranes via membrane condensation and membrane hydrolysis.