Multifunctional PVDF Membrane Coated with ZnO-Ag Nanocomposites for Wastewater Treatment and Fouling Mitigation: Factorial and Mechanism Analyses

In this study, a multifunctional poly(vinylidene fluoride) (PVDF) membrane was developed through chemical binding with ZnO-Ag nanocomposites to increase wastewater treatment efficiency. The unique characteristics of ZnO-Ag nanocomposites endowed the membrane with high surface hydrophilicity, organic/bio fouling resistance, and photocatalytic antibacterial activity. The significantly decreased water contact angle and increased under-water oil contact angle suggested improved surface hydrophilicity and organic fouling resistance. Through factorial analysis, it was found that the antibacterial activity of the multifunctional membrane could be significantly improved under visible light condition and with ZnO-Ag nanocomposites which obtained under higher Ag concentration and sintering temperature. The increase of Ag composition of ZnO-Ag nanocomposites on modified membrane surface significantly improved the membrane antibacterial activity but had little effect on membrane hydrophilicity. In addition, the photocatalytic antibacterial activity of ZnO-Ag nanocomposites could further improve the membrane biofouling resistance through simple exposure to visible light. The effects of different Ag chemical states on the performances of ZnO-Ag nanocomposites and the corresponding modified membranes were studied, and the relevant mechanism of antibacterial activity under both dark and light conditions was discussed. Filtration experiments with secondary wastewater effluent as feed solution indicated that the developed membrane exhibited one order of magnitude larger permeate flux compared to the pristine PVDF membrane, while maintaining comparable bacteria rejection rates during the filtration process.