Evaluation of nano/micro structured TiO2 films inactivation of multidrug-resistant E. coli 226 in greywater

Abstract

This study evaluates the performance of nano/micro-structured TiO2 films synthesized by Atomic Layer Deposition (ALD) and the Peroxo sol-gel (PSG) method using titanium isopropoxide (TTIP) as precursor, focusing on their structural properties and photocatalytic activity for greywater disinfection. A general factorial design was implemented by varying the annealing temperature from 300 to 600 °C under nitrogen to promote the formation of the anatase phase. The photocatalytic response was assessed through the inactivation of Escherichia coli 226 in real greywater. SEM analysis revealed that ALD films exhibited uniform and compact layers with thicknesses close to 20 nm, whereas PSG films showed polydisperse morphologies with irregular particle distribution and an average thickness of approximately 1 µm. XRD characterization demonstrated that 550 °C was the optimal annealing temperature to achieve well-defined anatase crystallinity for both deposition techniques. Optical and electrical analyses indicated that increasing temperature reduced the band gap and modified resistivity, with notable differences associated with each synthesis route. Photocatalytic experiments showed that PSG films achieved the highest bacterial inactivation, reaching 66.4 ± 0.1 % removal of E. coli 226 after 30 min, compared with 39.5 ± 0.3 % for ALD films and 17.1 ± 0.3 % under UV irradiation alone. These results demonstrate that TiO₂ films prepared via the PSG route and annealed at 550 °C constitute a more effective alternative for greywater treatment, outperforming both ALD-derived films and UV photolysis and highlighting the relevance of microstructural features and thermal treatment in determining photocatalytic efficiency.