Compatibility of antireflective coatings on glass for solar applications with photocatalytic properties

Antireflective coatings for solar cover glasses and photocatalytic coatings for self-cleaning glasses are two types of nano-functionalized thin films, which are extensively investigated at present. Broadband antireflective coatings typically receive their function by the low refractive index of nano-porous silica (<1.4), whereas the most established photocatalytic coatings consist of high refractive index materials, such as titania (>2.0). Compatibility of these two functional materials was investigated using sol-gel dipcoating-technology. Therefore silica sol, used to prepare nano-porous antireflective coatings, was mixed with different amounts of titanium n-butoxide to achieve titania concentrations in the range from 1 to 50 wt%. The fired coatings on silica glass showed a decrease in solar transmittance and an increase in photocatalytic activity with increasing titania concentration. With respect to applications in solar energy conversion systems compatible SiO2-TiO2 materials of low titania fractions (10 wt%) were established, which combine minor loss in transmittance and exceptional high photocatalytic activity. In comparison to conventional nano-porous silica, the decrease in the solar transmittance was only 0.7%, whereas the degradation rate of stearic acid was 30 times faster. (C) 2011 Elsevier Ltd. All rights reserved.