Abstract
TiO2 thin films are used extensively for a broad range of applications including environmental remediation, self-cleaning technologies (windows, building exteriors, and textiles), water splitting, antibacterial, and biomedical surfaces. While a broad range of methods such as wet-chemical synthesis techniques, chemical vapor deposition (CVD), and physical vapor deposition (PVD) have been developed for preparation of TiO2 thin films, PVD techniques allow a good control of the homogeneity and thickness as well as provide a good film adhesion. On the other hand, the choice of the PVD technique enormously influences the photocatalytic performance of the TiO2 layer to be deposited. Three important parameters play an important role on the photocatalytic performance of TiO2 thin films: first, the different pathways in crystallization (nucleation and growth); second, anatase/rutile formation; and third, surface area at the interface to the reactants. This study aims to provide a review regarding some strategies developed by our research group in recent years to improve the photocatalytic performance of TiO2 thin films. An innovative approach, which uses thermally induced nanocrack networks as an effective tool to enhance the photocatalytic performance of sputter deposited TiO2 thin films, is presented. Plasmonic and non-plasmonic enhancement of photocatalytic performance by decorating TiO2 thin films with metallic nanostructures are also briefly discussed by case studies. In addition to remediation applications, a new approach, which utilizes highly active photocatalytic TiO2 thin film for micro- and nanostructuring, is also presented.
Highlights
Among other semiconductors, TiO2 is the most extensively used photocatalyst for environmental remediation and energy harvesting applications due to its low cost, chemically inertness, non-toxicity, high photocatalytic activity, and recyclability [1]
We mainly discuss the deposition of the TiO2 thin films by electron beam evaporation and pulsed unipolar DC magnetron sputtering from a metallic target in a reactive O2 /Ar atmosphere to understand their differences in terms of the microstructure and resulting properties affecting photocatalysis
We reported self-organization of a network of nanoscopic cracks within a TiO2 thin film that was deposited by reactive sputtering and subjected to a post-deposition heat treatment [17]
Summary
TiO2 is the most extensively used photocatalyst for environmental remediation (e.g., water cleaning and air purification) and energy harvesting (e.g., water splitting for hydrogen generation) applications due to its low cost, chemically inertness, non-toxicity, high photocatalytic activity, and recyclability [1]. While the top NPs layer enhances photocatalytic efficiency, the bottom layer provides high stability We demonstrated another effective process, which basically allows controlled nano-crack network formation within sputter deposited TiO2 thin films, to achieve a high surface area [17]. These dopants can be metals (noble and transition metals), as well as non-metals, including elements such as N, B, S, and C [18,19] Noble metals such as Ag, Au, Pd, and Pt exhibit superior absorption properties owing to the surface plasmon resonance (SPR), but their high cost limits their use, especially in large scale applications [20]. Decorating TiO2 thin films with metallic nanostructures such as Au and Ag NPs is another effective approach to enhance photocatalytic efficiency through the localized surface plasmon resonance (LSPR). We presented a new approach which uses highly active TiO2 thin film as a functional tool for micro- and nanostructuring of surfaces
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