Abstract
Nano-size EVONIK AEROXIDE® P25 titanium dioxide, TiO2, powder was heat-treated at temperatures, 700–900°C, in air. An X-ray diffraction study showed that the P25 powder is composed of approximately 20 and approximately 80 mass% of rutile and anatase phases, respectively. It was also shown that the transformation from anatase to rutile induced by high-temperature heat treatment was almost completed at 750°C, whereas a small amount (less than 3 mass%) of anatase phase was still left even in the powder heat-treated at 900°C. The transformation behaviour was consistent with results obtained by Raman scattering spectroscopy. Raman experiments also indicated that high-temperature heating induced the formation of oxide ion vacancies. Powders were dispersed in methyl orange (MO) aqueous solution, and the bleach rate of MO was measured to evaluate photocatalytic activity under ultraviolet (UV)- and visible-light irradiation. After the heat treatment, the UV-light photocatalytic performance sharply deteriorated. Interestingly, visible-light photocatalytic activity was enhanced by high-temperature heating and reached the highest performance for an 800°C-heated sample, indicating that the P25 powder obtained high visible-light photocatalytic performance after heat treatment. Even after 900°C heat treatment, the photocatalytic performance was higher than that of as-received powder. Enhancement of photocatalytic activities was discussed in relation to visible light absorption and charge carrier transfer.
Highlights
Titanium dioxide, TiO2, is a most promising photocatalyst owing to its outstanding properties such as excellent photocatalytic activity, non-toxicity, and long-term thermal, chemical and physical stabilities [1]
Particle morphology was observed by a field-emission scanning electron microscope (FE-SEM) (SU8020, Hitachi High-Technologies Corp., Tokyo, Japan)
For the P25 powders after the heat treatment at 700–900°CDGÃrutile, the relative intensities of the anatase (101) diffraction peaks decreased, whereas those of the rutile (110) diffraction peaks increased. These opposite trends indicate that a phase transformation from anatase to rutile occurred at high temperature
Summary
TiO2, is a most promising photocatalyst owing to its outstanding properties such as excellent photocatalytic activity, non-toxicity, and long-term thermal, chemical and physical stabilities [1]. 45%), any shift in its optical response from UV to the visible spectral range will have a remarkable positive effect on the practical application of the material Another problem comes from the transformation from the metastable anatase phase to the thermodynamically stable rutile phase. TiO2 has been widely applied to be coated on tile, ground tile or other surface as functional layers, or to be immobilized on a substrate to construct the structured photocatalyst, in order to meet the requirement for practical applications Under such situations, hightemperature heat treatment for getting better binding force and preserving high photocatalytic ability after calcination are essential. Grain growth is inevitable to occur, resulting in decreased specific surface area and the reduced photocatalytic activities This has greatly limited the application of TiO2, and it should be crucially important to pursue high-performance TiO2 photocatalysts with both high visible light activity and thermal stability
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