Abstract
TiO2 thin films are promising as photocatalysts to decompose organic compounds. In this study, TiO2 thin films were deposited by reactive radio-frequency (RF) magnetron sputtering under various flow rates of oxygen and argon gas. The results show that the photocatalytic activity decreases as the oxygen-gas ratio is increased to 30% or less, while the activity increases under oxygen-rich conditions. It was observed that the crystal structure changed from anatase to a composite of anatase and rutile, where the oxygen-gas ratio during RF sputtering is more than 40%. Interestingly, the oxygen vacancy concentration increased under oxygen-rich conditions, where the oxygen-gas ratio is more than 40%. The sample prepared under the most enriched oxygen condition, 70%, among our experiments exhibited the highest concentration of oxygen vacancy and the highest photocatalytic activity. Both the oxygen vacancies and the composite of anatase and rutile structure in the TiO2 films deposited under oxygen-rich conditions are considered responsible for the enhanced photocatalysis.
Highlights
Thin films of photocatalysts have been intensively studied as clean technology [1,2,3]
Zhang et al reported that TiO2 film deposited under a high argon flow rate absorbs more light irradiation, which results in more electron–hole pairs generated in the TiO2 film and enhanced photocatalytic activity [17]
Huang et al and Chiou et al demonstrated that the photocatalytic activity of TiO2 films is raised with increasing oxygen flow rate to some extent but dropped at the high values of RO2 [18,19]
Summary
Thin films of photocatalysts have been intensively studied as clean technology [1,2,3]. It is possible to form films with various electronic states and microstructures via changing sputtering conditions, such as RF power, deposition pressure, substrate temperature, and gas flow rate. It is the characteristic of reactive sputtering that can control oxygen contents. Zhang et al reported that TiO2 film deposited under a high argon flow rate absorbs more light irradiation, which results in more electron–hole pairs generated in the TiO2 film and enhanced photocatalytic activity [17]. Huang et al and Chiou et al demonstrated that the photocatalytic activity of TiO2 films is raised with increasing oxygen flow rate to some extent but dropped at the high values of RO2 [18,19]. The wide range of RO2 conditions was not tested without heating substrate (see Table S1 in Supporting Information)
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