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Research Papers

SiO2 /TiO2 Antireflective Coatings With Photocatalytic Properties Prepared by Sol–Gel for Solar Glass Covers

[+] Author and Article Information
G. San Vicente1

A. Morales, N. Germán

 Departamento de Energía (CIEMAT), Unidad de Concentración Solar–Plataforma Solar de Almería, Avenida Complutense 40, E-28040 Madrid, Spain

S. Suarez, B. Sánchez

 Aplicaciones Medioambientales de la Energía Solar-División de Energías Renovables, Departamento de Energía (CIEMAT), Avenida Complutense 40, E-28040 Madrid, Spain

1

Corresponding author.

J. Sol. Energy Eng 134(4), 041011 (Sep 21, 2012) (5 pages) doi:10.1115/1.4007298 History: Received February 15, 2012; Revised July 23, 2012; Published September 21, 2012; Online September 21, 2012

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.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Effect of the TbuTi:ethanol molar ratio on the transmittance spectra for TiO2 coated borosilicate glass samples

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Figure 2

Effect of adding Triton X-100 on the transmittance spectra for TiO2 samples

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Figure 3

Transmittance spectra for uncoated borosilicate glass, AR coated borosilicate glass, and AR coated borosilicate glass after depositing the TiO2 layer

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Figure 4

Transmittance spectra of uncoated borosilicate glass, optimized AR coated borosilicate glass, optimized bifunctional ARSC coated borosilicate glass, and AM 1.5 solar photon spectral distribution (left). Photographs of the samples (right).

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Figure 5

(a) The absorbance spectra of MB peak before and after 3 h under UV illumination. (b) Time dependence of MB concentration during photodegradation test for TiO2 films of different thicknesses. Co is the initial MB concentration.

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Figure 6

Evolution of TCE and CO2 concentration with reaction time during the different steps carried out for evaluation of the photocatalytic activity of AR10 coated glass with three layers of TiO2 deposited at 30 cm/min

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Figure 7

Comparative results of the trichloroethylene conversion at steady state conditions along to solar transmittance values for samples with different TiO2 layers (left). Transmittance spectra obtained for the samples with different TiO2 layers (right).

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