Development of multifunctional sol–gel coatings: Anti-reflection coatings with enhanced self-cleaning capacity

The development of novel multifunctional coatings plays a crucial role in the achievement of more competitive architectural glasses and glazing materials for solar applications, among others. In this respect, coatings that provide high transmittance together with self-cleaning capacity could mean an added value to such glasses and glazing materials. Herein we report design and preparation of novel multifunctional (MF) coatings that present anti-reflection (AR) and self-cleaning (SC) capacity. First of all, preparation conditions of AR and SC coatings were optimized separately. The nano-structure and film thickness were carefully controlled by the solvent and the template agent ratio, in order to direct the refraction index and transmittance of each layer. Acquired experience allowed the fabrication of MF coatings consisting of two-layer stacks with a mesoporous SiO2 AR layer and a dense/mesoporous TiO2 layer. Regarding the anti-reflection capacity, MF and AR coatings present a net solar transmittance of 95.9% and 96.6%, respectively. Photocatalytic evaluation of the prepared SC and MF coatings showed that the mesoporous TiO2 layers can reach a higher photodegradation degree of organic matter than dense TiO2 layers. It is worth mentioning that the synergy between the AR and SC layers, promote a marked enhancement of the self-cleaning capacity of the MF coatings, exceeding in a 25–30% the photodegradation degree achieved with the commonly used porous or compact TiO2 coatings.