Construction of ZIF-8 composited hydrogel coated PVDF membrane with durable superhydrophilicity and dyes adsorption properties for efficient separation of emulsified and dyed wastewater

The complex wastewater contaminated with oil and organic dyes tremendously threatens ecological environment and human habitat. The single functional membrane separation technology is not qualified to deal with complex wastewater treatment. Therefore, it is necessary to develop multifunctional membrane materials possess the ability to both oil/water separation and organic dye adsorption. Hence, we develop a simple and environmental strategy to incorporate zeolitic imidazolate framework-8 (ZIF-8) as the nanomaterial adsorbents into superhydrophilic hydrogel coated PVDF membrane through in-situ growth and gained the anti-oil fouling and dye adsorption properties. The prepared tannic acid-poly(acrylamide-co-acrylic acid)-sodium alginate@ZIF-8 (TPS@ZIF-8) hydrogel coated PVDF membrane exhibited high oil-in-water emulsion separation efficiency of 99.77% after 10 cycles of separation and outstanding anti-oil fouling property that flux recover rate more than 96.86% in the continuous filtration experiment, owing to the strong hydration ability of TPS@ZIF-8 hydrogel coating. Moreover, the abundant adsorption active sites (including imidazole ring, –COO–, phenolic hydroxyl and benzene ring) consisted by ZIF-8 adsorbent and hydrophilic functional groups on the TPS@ZIF-8-PVDF improved the dye adsorption capacity and exhibited selective cationic dye adsorption with efficiency over 98.7% after multiple cycles of dye filtration adsorption test. The adsorption process of TPS@ZIF-8-PVDF membrane for methylene blue (MB) followed the pseudo-second-order kinetic model and Langmuir adsorption model. Incorporating the dye adsorption performance of ZIF-8 nanomaterials with underwater superoleophobic property of TPS hydrogel coated separation membrane, the prepared ZIF-8 composited hydrogel coated PVDF membrane could simultaneously separate the MB dyed oil-in-water emulsion mixtures and showed cycle performance stability (separation over 99.7%). Furthermore, TPS@ZIF-8-PVDF membrane could maintain the superwetting and dye adsorption properties in various chemical/mechanical environments and even friction test. This study offers new insights into the design of multifunctional superwetting hydrogel coated membrane for complex wastewater treatment and purification.