Unraveling the Multiple Effects Originating the Increased Oxidative Photoactivity of {001}-Facet Enriched Anatase TiO2

Crystal shape control on a series of anatase photocatalysts was achieved by varying the amount of HF employed as a capping agent in their hydrothermal synthesis. A systematic comparison between their physico-chemical properties, determined by several complementary surface and bulk techniques, before and after thermal treatment at 500 °C, allowed one to discern the influence of the relative amount of exposed {001} crystal facets among a series of effects simultaneously affecting their oxidative photocatalytic activity. The results of both formic acid and terephthalic acid photooxidation test reactions point to the primary role played by calcination in making {001} facets effectively photoactive. Annealing not only removes most of the residual fluorine capping agent from the photocatalyst surface, thus favoring substrate adsorption, but also produces morphological modifications to a crystal packing which makes accessible a larger portion of surface {001} facets, due to unpiling of plate-like crystals. The photocatalyst bearing the highest amount of exposed {001} facets (60%) shows the highest photoactivity in both direct and •OH radical mediated photocatalytic test reaction, also thanks to its very peculiar nanosheets aggregation.