Co-deposition enhances electrodialysis of thin film composite (TFC) membranes for efficient separation of Cl−/SO42-

Abstract

The increasing demand for monovalent anion separation necessitates the development of highly efficient and cost-effective monovalent selective membrane. In this study, thin-film composite (TFC) membranes were fabricated via a co-deposition method and applied in an electrodialysis system for Cl⁻/SO₄²⁻ separation. The high density of amine groups in the membrane enhances ion exchange performance, while the dense cross-linked structure and residual carboxyl groups formed after the interfacial polymerization (IP) reaction restrict SO₄²⁻ transport due to limited pore size and strong electrostatic repulsion. In contrast, the membrane exhibits high permeability for Cl⁻, enabling efficient separation of the two anions. The TFC membrane prepared by IP followed by co-deposition of 0.2 wt% Polyethyleneimine (PEI) and 0.2 wt% dopamine (DA) demonstrated excellent separation performance. At a current density of 100 A m⁻², the flux of Cl⁻ was 24.62 × 10⁻⁷(mol·cm⁻²·min⁻¹), while the flux of SO₄²⁻ was only 0.31 × 10⁻⁷(mol·cm⁻²·min⁻¹), with a selection factor of 80.5, the selection factor is 17 times higher than that of commercial monovalent anion exchange membranes. The prepared TFC membranes exhibited excellent stability, maintaining consistent ionic fluxes of 23.79 × 10⁻⁷ mol cm⁻²·min⁻¹ for Cl⁻ and 0.27 × 10⁻⁷ mol cm⁻²·min⁻¹ for SO₄²⁻, respectively. Seven consecutive cycling experiments proves good stability of the membrane. This demonstrates their great potential for industrial applications.