Two-layer asymmetrical ceramic membranes modified with Ag-ZnO for enhanced dye removal and antibacterial activity

The modification of low-cost ceramic membranes through the incorporation of nanomaterials offers a transformative approach to optimizing pore structure, surface chemistry, contaminant removal and introducing antimicrobial activity. In this study, low-cost ceramic membranes prepared from coal fly ash and natural sand were functionalized with plant-mediated Ag-doped ZnO nanoparticles of varying concentrations (0.25, 0.50, and 0.75 g) to enhance their filtration efficiency and antimicrobial capacity. The obtained functionalized membrane was characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS). Its antibacterial activity was evaluated against common pathogenic bacteria. Their physicochemical properties, including porosity, mechanical strength, water absorption, surface properties and chemical stability, were also thoroughly characterized. The fabricated functionalized membranes exhibited remarkable chemical stability in both acidic and basic solutions, demonstrating 31.4% porosity, an average pore size of 0.03 μm and a pure water flux of 42.13 L/m 2 /h. The filtration studies showed that the Ag-doped ZnO-functionalized ceramic membrane (FCM@0.50) achieved superior removal of Crystal violet compared to the pristine ceramic membrane, with 95% and 78% removal, respectively, within the first 20 min of the process. This enhanced performance is attributed to the functionalized membrane's negative surface charge at pH 8, which promotes electrostatic attraction to the cationic dye, and to reduced pore diameters that improve size-exclusion efficiency. Interestingly, the functionalized ceramic membranes exhibited concentration-dependent bacterial inhibition, achieving approximately 75%, 89%, and 92% inhibition efficiencies for samples containing 0.25, 0.50, and 0.75 g of Ag-ZnO NPs, respectively. Overall, the study promotes waste reduction and resource efficiency, contributing to the development of eco-friendly and effective wastewater treatment and antimicrobial technologies that align with the Sustainable Development Goals (SDGs).