Photocatalytic activity of specific facet-dominated anatase TiO2 in oxidation reactions

The electronic and surface properties of anatase TiO2 greatly influence its efficiency in photocatalytic processes. Therefore the preparation of shape-controlled titania may help in understanding the role played by specific crystal facets in favoring selective photoreactions. In the present work a series of anatase TiO2 materials were prepared by employing the hydrothermal route in the presence of titanium isopropoxide as Ti precursor and HF as capping agent, which allows the preferential stabilization of the less stable but potentially more reactive {001} facets. The effects induced by varying the F/Ti molar ratio (in the 0.1 – 2 range) on the structural and surface TiO2 properties was investigated. All powders were characterized by XRPD, BET, SEM and HR-TEM analysis and their efficiency was studied in formic acid mineralization. This reaction appears to be favored by a larger amount of {001} crystal facets, characterized by a suitable arrangement and coordination of surface atoms. Furthermore, the presence of residual surface fluoride was found to affect photoactivity. In fact, the thermal treatment applied to the as-synthesized materials produced a marked beneficial effect not only by removing surface fluoride but also by triggering morphological changes in the crystal aggregates.