Constructing Green Superhydrophilic and Superoleophobic Cofs-Mofs Hybrid-Based Membrane for Efficiently Emulsion Separation and Synchronous Removal of Microplastics, Dyes, and Pesticides

Abstract

Oil spills and micropollutants have become thorny environmental issues, posing serious threat to ecosystem and human health. To settle such dilemma, this study successfully constructed a robust and environmental-friendly MOFs-COFs hybrid-based membrane (FS-50/COF(MATPA)-MOF(Zr)/PDA@PVDF) for the first time through solution synthesis and solvothermal method, combined with surface modification of FS-50 molecule. Importantly, we employed a simple two-step strategy to obtain the high aspect ratio MOFs fibers: (1) solvent regulation to generate smaller needle-like whiskers; (2) high pressure induced directional crystallization in filtration process. Polydopamine (PDA) greatly improved the adhesion between coating and PVDF membrane. The in-situ growth of high length-diameter ratio MOFs fibers on blocky COFs greatly enhanced specific surface area of MOFs-COFs hybrid, thus provided sufficient absorption sites. FS-50 endowed hybrid membrane with superhydrophobicity and superoleophobicity, which facilitated to selectively penetrate water molecules and repel non-polar pollutants. The separation efficiency and decontamination mechanism of hybrid membrane to oily wastewater (containing various MPs, dyes, and pesticides) were investigated through experiments and theoretical calculations. Hybrid membrane could selectively and synchronously adsorb various dyes (20 mg/L–120 mg/L) and pesticides (10 mg/L) from oil-water emulsion. Large-scale coated sponge (6 cm × 4.5 cm × 3 cm) could quickly achieve separation of oil-water mixture (almost 100%) with water permeability of more than 162 L·m-2·h-1·bar-1, and simultaneously remove various MPs (PP-2000, PP-100, PE-2000, PS-100, 0.2 g/300 mL for each), Sudan Ⅲ (200 mg/L), and DIF (10 mg/L) from a simulant oily wastewater (300 mL), with the removal rates of almost 100% for MPs, 99.7% for Sudan Ⅲ, and 95.8% for DIF. Furthermore, we elucidated removal mechanism through simulating theoretical adsorption energy and potential adsorption sites. Hybrid membrane not only provides a promising candidate for the removal of multiple pollutants from oil-water emulsion, but also opens a new strategy for achieving efficient and clean aquatic environment restoration.

Keywords: Superhydrophilicity, Superoleophobicity, COFs, MOFs, Hybrid membrane