Dual application of TiO2- ZnO solar photocatalytic membranes in the degradation of oxy-tetracycline and inactivation of Staphylococcus aureus and Escherichia coli

Abstract

Oxy tetracycline (OTC) is a commonly used antibiotic and bio-recalcitrant environmental pollutant. Its persistence and accumulation in the environment contribute to antibiotic resistance, harming aquatic and terrestrial life. To address this, TiO₂-ZnO photocatalyst was synthesized and coated onto polyester membranes using the ex-situ method. They were characterized using Scanning Electron Microscopy (SEM) for morphology and Fourier Transform Infrared Spectroscopy (FTIR), Energy Dispersive X-ray Spectroscopy (EDX), and X-ray Diffraction (XRD) for structural analysis. Studies were conducted under natural sunlight using OTC (1–15 mg/L) and Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) bacteria (2.45 ×103 and 2.45 ×105 CFU/mL) at various solution pH. Antimicrobial activity was assessed using disk diffusion and glass bottle tests. The SEM and EDX analysis confirmed the incorporation of the photocatalyst within the membranes with no impurities. Shifted peaks of FTIR and XRD confirmed the interaction between the photocatalyst and the membranes. The findings indicated that OTC degradation (10 mg/L) improved with pH, achieving 87.6 % removal efficiency at pH 9. Disk diffusion tests using coated membranes achieved inhibition zones of 21 mm (E. coli) and 26 mm (S. aureus), while the glass bottle tests resulted in 100 % inactivation for both bacteria. In contrast, the uncoated membranes showed no inhibition zones and minimal disinfection (<1 %). The developed photocatalytic membranes demonstrated dual functionality in photodegradation of OTC and disinfection in water treatment. This was achieved by the release of reactive oxygen species that are effective against antibiotics, gram-positive and gram-negative bacteria.