The glass covers of solar systems are usually coated with antireflective (AR) coatings on both sides that allow to increase the efficiency of the whole system. At the same time, the accumulation of dust and dirt particles on the surface of the AR coated glass decreases the transmittance of the covers, even to values lower than the uncoated glass. This decrease in the cover transmittance reduces the solar radiation that reaches the absorber and, in this way, a decrease in the solar plant efficiency would be obtained. So, the use of films that combine high transmittance and self-cleaning capacity seems to be a promising development. This paper reports the preparation of sol–gel porous TiO2 and SiO2 bilayers on borosilicate glass. The porosity and thickness of both layers have been optimized in order to obtain the optimal photocatalytic and optical properties. Solar transmittance values of 0.964 were obtained for the TiO2/SiO2 coated glass. The highest value of transmittance reached is 0.993 and it is placed at 600 nm. The self-cleaning properties were evaluated using methylene blue and trichloroethylene (TCE) as model organic molecules using UV-A light. The results showed that the SiO2/TiO2 samples degraded the colorant faster than the SiO2 sample. Moreover, the degradation of TCE in air in a continuous fix bed photoreactor for samples with different TiO2 film thicknesses was also performed. The TCE conversion was found dependent on the TiO2 thickness. Nevertheless, the increase in the thickness of this layer reduced transmittance properties. The study demonstrates that it is possible to combine antireflective and self-cleaning properties in the same material.
Evaluation the use of nano metal oxides as potential self cleaning agents for stained archeological textiles