Uniform TiO2/In2O3 surface films effective in bacterial inactivation under visible light

• Sputtered antibacterial adhesive coating absorbing in the visible.
• Synergistic antibacterial action of TiO2–In2O3.
• TiO2–In2O3 composite induces a bacterial inactivation with high quantum yield.
• An interfacial charge transfer mechanism is suggested between TiO2 and In2O3.

This study shows that the surface modification of TiO2 is an effective route to increase the TiO2 absorption in the visible region up to ∼600 nm for photocatalytic applications. The In2O3 decorated TiO2 films on polyester obtained by reactive sputtering were shown to accelerate the Escherichia coli inactivation under actinic and simulated solar light. TiO2 sputtered films for 10 min inactivated bacteria within 300 min under actinic light. The inactivation time was reduced when using a TiO2 10 min–In2O3 10 s sample to 150 min when using actinic light and 90 min by simulated sunlight with 50 mW/cm2 (one half of AM1). Thinner TiO2–In2O3 coatings led to faster bacterial inactivation compared to thicker TiO2–In2O3 layers due to the reverse diffusion of the generated charges. The increase in the optical absorption of the green coloured TiO2–In2O3 film was a function of the In2O3 loading as detected by diffuse reflectance spectroscopy (DRS). Evidence of the lack of TiO2 lattice doping by the sputtered In2O3 was found by X-ray diffraction spectroscopy (XRD). The deconvolution of TiO2 bands detected by X-ray photoelectron spectroscopy (XPS) revealed the existence of Ti4+/Ti3+ signals suggesting redox catalysis at the surface of the TiO2–In2O3. The photo-induced interfacial charge transfer (IFCT) between TiO2 and In2O3 can be accounted for by the band position potentials of both semiconductors. The faster kinetics of TiO2–In2O3 inducing E. coli inactivation with a higher quantum efficiency compared to TiO2 takes place in spite of the low intensity of the IFCT optical absorption bands >400 nm.

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