Influence of Crystal Structure, Morphology and Sodium Ion on the Photocatalytic Reactivity of Spray Deposited Titanium Dioxide Film

Abstract

In this paper, three types of titanium dioxide structures (anatase, heated amorphous and amorphous) from peroxo titanium complex were deposited on glass and wafer substrates by spraying technique. Influences of crystal structure, morphology and sodium ion on UV induced hydrophilicity were studied. X-ray diffraction revealed that crystalline anatase coatings are extremely hydrophilic (<10°) under UV irradiation (indoor) while the amorphous coatings are still hydrophobic on both glass and wafer substrate with contact angles as high as 70º. When amorphous coating was heated at 450°C, its structure was converted into crystalline anatase, and hence its UV induced hydrophilicity behavior on wafer substrate became similar to that of anatase. However, this UV induced hydrophilicity was inhibited on heated glass (450°C), suggesting that sodium ions in the glass might be responsible for the differences between silicon wafer and glass. With increasing coating thickness, such inhibition effect was reduced, but the hydrophilicity still could not reach the level of anatase. After 6 months of outdoor exposure, water contact angle for amorphous, heated amorphous and anatase were 61°, 26.6° and 12.1°, respectively. Also, X-ray diffraction suggested that amorphous is not converted into anatase after long period of UV exposure, although coating morphologies are changed based on Scanning Electron Microscopic observation. It is concluded that the crystal structure, coating morphology and sodium ion concentration have key impact on the photocatalytic properties on glass substrate.