Photo-induced self-cleaning and hydrophilic properties of columnar TiO2 nanostructures obtained by glancing-angle magnetron sputtering

Abstract

Self-cleaning and anti-fogging technology is already used in a variety of the products today, among which glazing products prevail. Their function is based on two principles, either hydrophobicity (Lotus effect) or photocatalytic hydrophilicity. In the latter case, the self-cleaning action is based on the combination of photocatalysis and photoinduced superhydrophilicity, where dirt removal by uniform spreading of water over the whole surface is improved with photocatalytic decomposition of organic contaminants (Zhang et al., 2012). In spite of the high readiness level of this technology, with competitive products already in the market, there is room to improve the properties of existing self-cleaning and anti-fogging surfaces by designing and tailoring new nanoarchitectures for light-activated thin films (Lavrenčič Štangar et al., 2014). Among photoactive materials, TiO2 gathers nearly all the desired characteristics of a photocatalyst, with the main exception that it is only active under UV light and thus can only use around 5% of the solar spectrum. The synthesis and applications of titania 1D and 2D structures such as nanorods, nanowires and nanotubes has increased in the last decades due to their singular properties in terms of surface area, charge separation and transport, and tuneability (Fresno et al., 2014). In this work, we have obtained highly regular TiO2 nanostructures by oxidation of metallic Ti nanocolumns (NCs) obtained on silicon wafers by the so-called glancing angle deposition technique by magnetron sputtering (MS-GLAD). MS-GLAD is a powerful technique for producing nanostructured coatings in large areas and with a large variety of morphologies (Izquierdo-Barba et al., 2015). In addition, the TiO2 NCs have been decorated with gold nanoparticles (NPs) by means of high-power impulse magnetron sputtering (Mayoral et al., 2019).