Construction of MXene-based laminar membranes with aminated Fe3O4 via electrostatic self-assembly for selective dye/salt separation

Abstract

To address the long-standing trade-off between flux and selectivity, as well as the structural instability of conventional nanofiltration (NF) membranes, this study proposes a novel intercalation strategy for constructing two-dimensional laminar NF membranes based on MXene for efficient dye/salt separation. Spherical Fe₃O₄ nanoparticles were functionalized with amino groups using 3-aminopropyltriethoxysilane (APTES) to impart positive surface charges, and subsequently assembled onto hydrophilic MXene (Ti₃C₂T_x) nanosheets via electrostatic self-assembly, forming a structurally stable MXene/NH₂-Fe₃O₄ composite membrane. The surface functionalization of Fe₃O₄ plays a critical role in regulating the interlayer structure of MXene, thereby enhancing membrane stability and selective transport performance. At a mass ratio of MXene to NH₂-Fe₃O₄ of 1:6, the membrane exhibited a pure water flux of 136.6 L/(m²·h) and rejection rates of up to 99.9 % for Congo Red (CR) and Evans Blue (EB). In contrast, the rejection rates for NaCl, MgSO₄, and Na₂SO₄ were 7.0 %, 15.4 %, and 26.4 %, respectively. In mixed dye/salt systems, the membrane exhibited excellent selectivity, with separation factors of 839 for CR/NaCl, 704 for CR/MgSO₄, and 566 for CR/Na₂SO₄, attributed to synergistic contributions of size exclusion, electrostatic repulsion, and the Donnan exclusion effect. Furthermore, the composite membrane demonstrated outstanding dye removal efficiency, acceptable salt rejection, and robust structural integrity under prolonged operation, wide pH variations, and challenging conditions involving organic foulants and surfactants, offering a practical strategy for developing advanced NF membranes for complex wastewater treatment.