A water-stable two-dimensional Zn(BDC) lamellar membranes for efficient molecular separation with enhanced water permeability

Abstract

Although 2D Zn(BDC) MOFs exhibit exceptional water stability, the synthesis of ultrathin 2D Zn(BDC) nanosheets has proven to be a formidable challenge. Conventional bottom-up methods suffer from limitations such as low yield and difficulties in eliminating surfactant molecules or end ligands, which are introduced to control the directional growth of 2D Zn(BDC). In this work, 2D Zn(BDC) nanosheets featuring a two-nuclear paddlewheel zinc structure were successfully synthesized through a three-phase synthesis method, exhibiting a thickness of about 2 nm. The 2D Zn(BDC) lamellar membranes were prepared through simple vacuum filtration. By adjusting the colloidal concentration of the 2D Zn(BDC) nanosheets, fine control over the resulting membrane thickness was achieved. Moreover, the incorporation of polyvinyl alcohol (PVA) as a cross-linking agent significantly enhanced the stability of the 2D Zn(BDC) lamellar membranes. The addition of PVA demonstrated effective regulation of pore size in the membrane, facilitating well-ordered stacking of nanosheets for superior screening efficiency in dye/ion separation applications. The permeability of 2D Zn(BDC) lamellar membranes was observed to be 372.9 L m−2 h−1 bar−1, while exhibiting a rejection rate exceeding 99.7 % for dye molecules, such as direct red (DR23), reactive black (RB5), chromium black T (CBT), Congo red (CR). The remarkable performance is ascribed to a synergistic effect between molecular sieving and electrostatic repulsion. 2D Zn(BDC) lamellar membranes exhibit exceptional long-term stability, and resistance to fouling and chlorine, thereby showcasing their immense potential for diverse applications in the realm of dye wastewater treatment.