Study On Metal/TiO₂Composite Film And Its Photocatalytic Properties At Visible Frequencies

Recently, semiconductor photocatalysis as a promising solution for conversion ofsolar energy into chemical energy has attracted a lot of attention. Among semiconductors,titanium-oxide (TiO2) is one of the most populate photocatalysts because of its relativelyhigh activity, chemical stability, availability with low production costs, and non-toxicity;however, its band-gap energy is wide and its quantum efficiency is low. More recently,significant efforts have been made to extend the photoactive response of TiO2to visiblelight and improve the quantum efficiency of TiO2. In this thesis, metal/TiO2hybridphotocatalysts are fabricated by magnetron sputtering, and are further shown to exhibitgreatly enhanced visible light photocatalysis at the localized surface plasmon resonances(LSPRs). The work presented is divided into two main sections.1. In the first section, a simple two-step method was developed to prepareAu-nanoparticles/TiO2composite films. First, TiO2and Au thin films are successivelydeposited onto a FTO glass using magnetron sputtering. The as-prepared films are thenpost annealed to transform the Au film to Au nanoparticles. In this process, the sizedistribution of Au nanoparticles can be easily controlled by controlling the annealingtemperature and the initial thickness of Au film. The optical and photocatalytic propertiesof the prepared composite films are investigated. It is found that the Au-nanoparticles/TiO2composite film can support localized surface plasmon resonances (LSPRs) in the visibleregion, and their resonant wavelengths can be tuned by varying the size distribution of Aunanoparticles. More importantly, compared with the pure TiO2film, the Au-nanoparticlesloaded TiO2films exhibit a remarkably enhanced photocurrent generation and asignificantly improved efficiency of photochemical water splitting under visible light irradiation.2. In the second section, we fabricated metal-semiconductor-metal (MSM) hybridphotocatalysts, composed of an opaque Au film, a thin TiO2film, and Au nanoparticles, byusing magnetron sputtering and post annealing. We investigated the optical andphotocatalytic properties of the hybrid photocatalysts. It is found that the MSMphotocatalysts can absorb much more visible light than pure TiO2andAu-nanoparticles/TiO2composite films do, and exhibit a broadband absorption of visiblelight in the spectral range from400nm to800nm. Correspondingly, the performance of thevisible light photocatalysis can be greatly improved in the MSM photocatalysts.Furthermore, we also investigated the effect of TiO2film thickness and Au nanoparticlesize distribution on the optical and photocatalytic properties of MSM photocatalysts.