Enhancing oil/water emulsion separation with inkjet printed beetle-inspired zeolitic imidazolate framework-67 modified membranes

Abstract

Efficient oil/water emulsion separation remains a critical challenge in industrial wastewater treatment due to the stability of emulsified oil droplets and the complexity of traditional membrane modification techniques. This study introduced a novel approach by employing a green, convenient, and controllable inkjet printing technique to fabricate a new inversely beetle-inspired hydrophobic zeolitic imidazolate framework-67 (ZIF-67) nanoparticle-modified tannic acid (TA)‑titanium (IV) bilayer structure on a polyvinylidene fluoride (PVDF) substrate. The resulting PVDF/TA-Ti(IV)/ZIF-67 membrane significantly enhanced the separation efficiency of oil/water emulsions. The TA-Ti(IV) layer not only enhanced the adhesion and uniform distribution of ZIF-67 but also minimized reagent consumption, simplifying the fabrication process. The hydrophobic ZIF-67 particles on the membrane served as localized active sites, facilitating the coalescence of small oil droplets within the emulsion, thus achieving effective demulsification and transforming stable oil-water emulsions into easily separable, unstable emulsions. This innovative membrane demonstrated optimal flux and rejection rates in oil/water emulsion separation. Its water flux exceeded 311.0 L·m⁻²·h⁻¹ in gasoline, diesel, and soybean oil emulsions, approximately 5.5 times that of the unmodified PVDF membrane, while maintaining an oil rejection rate of over 99.6 %. Remarkably, the PVDF/TA-Ti(IV)/ZIF-67 membrane retained over 99 % separation efficiency after six filtration cycles, underscoring its exceptional antifouling performance and long-term operational stability. The innovative membrane developed in this study offers a cost-effective, scalable, and environmentally sustainable solution for large-scale oil/water emulsion treatment. Its bio-inspired wetting structure significantly enhances flux, oil rejection, and antifouling capabilities, marking a major advancement in industrial water treatment applications.