Dual-tasking PVA-tannic acid-coated ZIF-8/PVDF blended membrane for simultaneous high-flux oil-water emulsion separation and Pb<sup>2</sup><sup>+</sup> adsorption.

Abstract

The concurrent treatment of oily wastewater containing heavy metal ions presents significant challenges for conventional membranes, primarily due to limitations in fouling resistance and multifunctionality. To address these issues, we developed a novel blended mesh membrane, designated as PVA-TZ_1.5P@PSSM, where the subscript 1.5 indicated 1.5 wt% of tannic acid-coated ZIF-8 (TA@ZIF-8) micro/nanocrystals in a polyvinylidene fluoride (PVDF) casting solution. The membrane was fabricated by integrating TA@ZIF-8 into a PVDF blend matrix (TZP), followed by hydrophilic modification with polyvinyl alcohol (PVA). This composite was then anchored onto a polydopamine-modified stainless steel mesh (PSSM) through a freeze-thaw crosslinking process. The resulting membrane exhibited exceptional superhydrophilicity (water contact angle ∼ 0°) and underwater superoleophobicity (underwater oil contact angle (UOCA) > 150°), leading to remarkable self-cleaning properties, anti-corrosion performance, and ultra-low oil adhesion. It achieved high-efficiency separation (> 97 %) of diverse oil-in-water (O/W) emulsions with outstanding permeation flux (> 4500 L·m^-²·h^-¹·bar^-¹) and maintained excellent chemical and mechanical stability across various harsh environments (pH 2-12), even after 30 separation cycles. Importantly, the membrane demonstrated significant capability for synergistic Pb²⁺ removal, achieving an adsorption capacity of 26.5 mg·g⁻¹ , which followed a monolayer chemisorption mechanism. This work provides a facile, cost-effective, and eco-friendly approach to fabricating multifunctional membranes for complex oily wastewater remediation.