Dual-functional tannic acid-infused AgNPs-PVDF membranes via coagulation methods: an integrated study on antibacterial and antifouling performances for oil-in-water separation

Recently, the development of dual-functional surfaces combining antibacterial and antifouling properties has remarkably gained significant attention in membrane separation technologies, particularly for oil-in-water separations. Herein, we present a novel approach to synthesizing PVDF mixed matrix membranes using the phase inversion process, with different concentrations of tannic acid and silver nitrate via the coagulation bath method of fabrication, a naturally inspired tannic acid (TA)-based green chemistry strategy to facilitate the simultaneous benefit of combining high antifouling ability as well as antibacterial activities. A controlled approach for the in situ incorporation of AgNPs into the mixed-matrix membrane was successfully achieved using an active coagulation bath. We have specifically focused on the various concentrations of TA in the membranes to serve as a multifunctional component via an exclusive coagulation method of fabrication, which further enables integration and dispersion of AgNPs into the PVDF matrix. As such, five different membranes (M-1 to M-5) with distinct amounts of TAs were prepared and investigated for their structural properties, primarily antibacterial activities and separation performances, including pure water flux in cross-flow filtration and rejection of an oil-in-water emulsion. The M-2 and M-3 membranes, containing moderate amounts of tannic acid, demonstrated superior rejection and flux recovery with more than 90% oil-in-water emulsion. These membranes also exhibited optimized performance in antifouling resistance when tested with synthetic natural organic matter (NOM) solutions. Most interestingly, all the membranes showed extraordinary antibacterial properties against E. coli when tested with the disk diffusion method. Overall, the unique surface chemistry obtained by synergistic effects of the TA-AgNPs combination resulted in enhanced performance of these membranes toward superior antibacterial and desirable antifouling properties, yielding new PVDF matrix candidates for advanced oily wastewater treatments.