Antibacterial Properties of TiO2 Film Improved by Hydrogen Reduction Heat Treatment

Titanium dioxide (TiO2) has good photocatalytic activity and can degrade environmental pollutants by oxidation. It has been used in photocatalysis, on antibacterial, antifouling and self-cleaning surfaces, and ultraviolet (UV) detectors. However, it predominantly absorbs UV light and has low absorption of visible light. Improving antibacterial efficiency in the visible light region has consistently been a key research direction for TiO2 antibacterial properties. Currently, to improve TiO2 photocatalytic efficiency under visible light, multiple schemes have been proposed, such as metal or non-metal doping, and laser surface or vacuum heat treatment. These methods introduce point defects in the TiO2 lattice, and narrow the band gap by changing the semiconductor energy band and introducing impurities or defect energy levels in the band gap, thus enhancing visible light absorption. To better understand the TiO2 antibacterial mechanism, it is necessary to accurately control its morphology, composition, and crystal structure. Thin film materials adequately meet these requirements. Recently, pulsed laser deposition (PLD) has become a widely adopted film deposition technology owing to its simple system setup, wide range of deposition conditions, material selection and ability to prepare high-quality repeatable films. In this study, TiO2 thin films are prepared using PLD, and the oxygen vacancy concentration on the TiO2 surface is increased by hydrogen reduction heat treatment to enhance its antibacterial properties. Results demonstrate that the TiO2 films grown on a single crystal yttria stabilized zirconia (YSZ) substrate are the highly preferred anatase phase, and the higher the growth temperature, the stronger the X-ray diffraction (XRD) peak of the anatase phase and the denser the film. The antibacterial properties of 350 nm thick TiO2 film grown at 600 celcius were measured and it was identified that the antibacterial rate is approximately 86%. The sample was further reduced in a 4% H2 atmosphere, and it was confirmed that the antibacterial rate increased to approximately 97%. Test results demonstrate that through X-ray photoelectron spectroscopy (XPS), a UV-visible spectrophotometer (UV-visible) and a laser Raman spectrometer (PL), additional oxygen vacancies formed on the TiO2 surface after reduction heat treatment, and oxygen vacancy defect energy levels formed in the TiO2 band gap. This resulted in enhanced light absorption in the visible region and higher antibacterial performance. The material defect is controlled by the hydrogen reduction process, and the TiO2 thin film photocatalytic antibacterial property and antibacterial mechanism were studied. This straightforward method for regulating TiO2 light absorption provides technical feasibility for scale growth.