Aqueous phase co-solvent-assisted preparation of high-performance polyamide nanofiltration membranes: Preparation, performance and mechanistic

Abstract

Co-solvent-assisted interfacial polymerization is commonly used to enhance the characteristics of polyamide (PA) thin film composite (TFC) membranes. However, its application to PIP-TMC systems is less frequent, and there is limited understanding regarding the role of co-solvents. In this article, we selected N, N-dimethylacetamide (DMAc), 1-butanol, acetonitrile (ACN), and N-methyl pyrrolidone (NMP) with similar solubility parameters to modulate the PIP-TMC IP process. The introduction of co-solvents can enhance the mutual solubility between aqueous and organic phases, which promotes the PIP diffusion rate and contributes to high-performance NF membranes characterized by smaller pore sizes. Notably, membranes prepared with DMAc demonstrated enhanced retention of divalent ions (MgCl₂: from 41 % to 83.4 %) and maintained high permeability (46.6Lm⁻² h⁻¹ at 0.3 MPa), whereas excessive co-solvents could damage the performance. Additionally, Molecular dynamics (MD) simulations show that the co-solvent regulates PIP diffusion rate with its diffusion rate by hydrogen bonding with the PIP molecules and moving together with PIP. Significant variations in the PIP diffusion rate resulted in a wrinkled morphology on the membrane surface. This study offers fresh insights into the selection of co-solvents for co-solvent-assisted TFC NF membrane preparation, presenting a straightforward, facile, and commercially viable approach for achieving high-performance NF membranes.