Nano-crystals of titanium dioxide in aluminum oxide: A transparent self-cleaning coating applicable to solar energy

• Coatings exhibit sunlight-activated self-cleaning and hydrophilic characteristics.
• Self-cleaning coating on glass with enhanced transparency (up to 91%) to visible light over uncoated glass (90%).
• Photoactive self-cleaning coatings deposited on surfaces other than glass.

A novel coating on soda-lime glass provided both self-cleaning properties, when exposed to sunlight, and high optical transparency (up to 91%). This coating was obtained from a dispersion of titanium dioxide nanocrystals in an aqueous hydrochloric acid solution of aluminum triisopropoxide. Applying this suspension to the glass substrate, and then heating 400 °C, resulted in a coating remaining on the glass surface. Interestingly, the transmission of light through the coated glass is slightly increased by circa 1–2% in the visible region (400–850 nm). The alumina/titanium dioxide coated glass exhibits photocatalytic activity on exposure to ultraviolat light (255 and 366 nm) in a laboratory setting and when placed in natural sunlight. A preliminary field test was conducted where samples of uncoated glass and alumina/titanium dioxide coated glass where placed outdoor side-by-side for two months. Uncoated glass samples became soiled resulting in a decreased transparency to circa 73–80%T at 580 nm (90%T at 580 nm when clean). In contrast the coated glass samples decreased only slightly to circa 90%T at 580 nm (91%T at 580 nm when clean). Substrates other than soda lime glass were also coated with a film of alumina/titanium dioxide without adversely affecting the properties of the substrate while providing photocatalytic activity.

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