Co/SH-based MOFs incorporated nanofiltration membranes for efficient selenium uptake in water purification

Metal-Organic Frameworks (MOFs) with high adsorption capacity have shown potential in removing pollutants from water, particularly the toxic selenium (Se). However, MOFs face two challenges in the application of Se removal, that is low removal efficiency and unfavorable powder properties for recovery. In this study, a Co-MOF-74-SH with dual active adsorption sites was synthesized and subsequently immobilized into membrane to fabricate a multi-functional nanofiltration (NF) membrane for efficient Se removal and salt-salt separation. The strong cooperative interaction between the dual active Co/S sites and Se resulted in an impressive Se removal efficiency of 94.1 % for Co-MOF-74-SH. The adsorption energy and isosurface of electron density from DFT simulations showed the strong interaction between SeO₃^2- and S sites in Co-MOF-74-SH. NF membrane with Co-MOF-74-SH incorporation was fabricated. This membrane showed Se removal of ∼99.6 %, surpassing original membrane of ∼74.4 %, which was attributed to synergetic mechanism of adsorption and separation. Simultaneously, the membrane exhibited excellent separation performance, with divalent/monovalent salt selectivity up to more than 80 as well as high water permeance of 15.80 L m^-2 h^-1 bar^-1. This work not only broadens efficient adsorbents for Se removal, but also paves the way for membrane material for water purification and wastewater resource utilization.