Exceptional Photocatalytic Activity of 001-Facet-Exposed TiO2 Mainly Depending on Enhanced Adsorbed Oxygen by Residual Hydrogen Fluoride

详细信息    查看全文

• 作者：Yunbo Luan ; Liqiang Jing ; Ying Xie ; Xiaojun Sun ; Yujie Feng ; Honggang Fu
• 刊名：ACS Catalysis
• 出版年：2013
• 出版时间：June 7, 2013
• 年：2013
• 卷：3
• 期：6
• 页码：1378-1385
• 全文大小：417K
• 年卷期：v.3,no.6(June 7, 2013)
• ISSN：2155-5435

文摘

Is it true that the exceptional photocatalytic activity of 001-facet-exposed TiO₂ is attributed to its high-energy surfaces? In this work, nanocrystalline anatase TiO₂ with different percentages of the exposed (001) facet has been controllably synthesized with a hydrothermal process using hydrofluoric acid as a morphology-directing agent. It is shown that the percentage of (001)-facet exposure is tuned from 6 to 73% by increasing the amount of used hydrofluoric acid, and meanwhile the amount of residual fluoride in the as-prepared TiO₂ is gradually increased. As the percentage of (001) facet is increased, the corresponding TiO₂ gradually exhibits much high photocatalytic activity for degrading gas-phase acetaldehyde and liquid-phase phenol. It was unexpected that the photocatalytic activity would obviously decrease when the residual fluoride was washed off with NaOH solution. By comparing F-free 001-facet-exposed TiO₂ with the F-residual one, it is concluded that the exceptional photocatalytic activity of the as-prepared 001-facet-exposed TiO₂ depends mainly on the residual hydrogen fluoride linked to the surfaces of TiO₂ via the coordination bonds between Ti⁴⁺ and F鈥?/sup>, as well as slightly on the high-energy 001-facet exposure, by means of the temperature-programmed desorption (TPD) measurements, the atmosphere-controlled surface photovoltage spectra, and the isoelectric point change. On the basis of the O₂-TPD tests, theoretical calculations, and O₂ electrochemical reduction behaviors, it is further suggested for the first time that the residual hydrogen fluoride as the form of 鈭扵i:F鈥揌 could greatly enhance the adsorption of O₂ so as to promote the photogenerated electrons captured by the adsorbed O₂, leading to the great increase in the charge separation and then in the photocatalytic activity. This work would clarify the high-activity mechanism of widely investigated TiO₂ with high-energy 001-facet exposure and also provide feasible routes to further improve photocatalytic activity of TiO₂ and other oxides.

Keywords:

exposed 001 facet; charge separation; residual hydrogen fluoride; adsorbed oxygen; TiO₂ photocatalysis