Abstract
Abstract Self-cleaning surfaces have excelled in recent years in energy and environmental fields. In particular, in solar energy area, these surfaces are used to avoid soiling accumulation on photovoltaic (PV) modules. So far TiO2 has been widely used due to its photocatalytic activity and photo-induced superhydrophilicity. However, this oxide has some limitations since it reduces the glass transmittance and it rapidly reestablish the water contact angle in dark environments. In order to circumvent these limitations, composites TiO2/SiO2 have been proposed. For photovoltaic application, besides a good transparency in the wavelength region 300–1800 nm and self-cleaning properties, the coating should also present long durability and adequate adhesion to endure the outdoor conditions. Aiming at developing a coating with these properties, in this work, TiO2/SiO2 composites containing different titanium content have been synthesized and compared with pure TiO2 films in relation to adhesion, transparency and hydrophilicity. Both films have been deposited over low iron float glass substrates by sol–gel dip-coating technique and different calcination temperatures (400, 500, 600°C) and Si/Ti molar rates (Si86Ti14, Si40Ti60) have been considered. TiO2/SiO2 films showed higher transmittance in visible range compared with pure TiO2. TiO2/SiO2 films showed superhydrophilic character before and after ultraviolet irradiation, with water contact angles near to 0°. Furthermore, as predicted, TiO2/SiO2 films could keep the superhydrophilic character in dark environments, in contrast with pure TiO2 films. Both TiO2 and TiO2/SiO2 films exhibited good adherence and it is shown that higher calcination temperatures and higher titanium content enhance such property. All films presented abrasion resistant property in contact with sponge and detergent. It has been demonstrated that high transmittance, self-cleaning and adherent composite has been obtained by a simple sol–gel route presenting good potential to be applied on photovoltaics systems.
Highlights
TiO2 is widely used as a photocatalyst and it can be applied in environmental and energy fields, including self-cleaning surfaces, air and water purification systems, antifogging surfaces, among others [1]
TiO2/SiO2 composite films showed high %T (>85%) in visible-NIR range, which is fundamental for solar energy application [14]
TiO2/SiO2 high transmittance, self-cleaning, abrasion resistant and adherent films were obtained by a simple sol–gel route. 500°C treated films showed better mechanical property with respect to 400°C treated films and better optical property with respect 600°C treated films
Summary
TiO2 is widely used as a photocatalyst and it can be applied in environmental and energy fields, including self-cleaning surfaces, air and water purification systems, antifogging surfaces, among others [1]. Jesus et al Applied Adhesion Science (2015) 3:5 contaminants adsorbed on film surface are decomposed under ultraviolet light [3] This property allows TiO2 to be applied in air and water purification systems as well as for self-cleaning surfaces. TiO2/SiO2 composite films can circumvent these limitations, slowing down the increase of water contact angle in dark environments and presenting higher transmittance with respect TiO2, which is essential for the application as a self-cleaning surface in solar energy area [2,6,7]. Self-cleaning surface are important for PV application, since the dust, pollution, and other particles accumulation reduce the transparency of the PV module cover glasses and decrease the electrical performances of the modules. Pure TiO2 and TiO2/SiO2 composite films containing different titanium content have been deposited over glass substrates by sol–gel dip-coating method aiming at obtaining super hydrophilic, adherent and transparent coating. The coatings have been compared and characterized regarding their optical, mechanical and microstructural properties
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