Engineering nano-nodular pattern on the substrate surface by tuning phase inversion to construct ultrapermselective ion-separation nanofiltration membrane

Abstract

Ion-selective permeable membranes show enormous potential in salt separation and resource recovery, but the permselectivity of current membranes restricts their broad application. Here, we presented a novel strategy for constructing a polyamide (PA) nanofiltration (NF) membrane with high water permeability, excellent divalent ion rejection, and outstanding Cl⁻/SO₄²⁻ selectivity via a facile substrate-tailored method. A nano-nodular substrate with some polyvinylpyrrolidone (PVP) on the surface was fabricated via vapor-induced phase inversion. This novel substrate with a unique pattern could duplicate the nano-nodule pattern on the PA layer and decrease the diffusion rate of piperazine (PIP) due to the open-nanodular structure with appropriate PVP on the surface. Consequently, a PA membrane with nano-nodular pattern, thin skin layer, narrow pore size distribution and negative charge was formed. The nano-nodular surface and thinner thickness exhibited a remarkable contribution to water permeability, which reached 38.3 L m⁻²h⁻¹bar⁻¹. The narrow pore size distribution made an outstanding Na₂SO₄ rejection of 99.1 % and Cl⁻/SO₄²⁻ selectivity of 83 at 1000 mg/L of mixed salt solution. The Cl⁻/SO₄²⁻ selectivity increased to 110 with 5000 mg/L of mixed salt solution. The permselectivity of this novel membrane was superior to the state-of-the-art NF membranes. This work pioneers a new approach to tuning the PA layer structure, which can be readily achieved, and offers a fresh perspective on constructing high-performance NF membranes.