Reversing the Photocatalytic Activity Orders of Anatase TiO2 Facets by Surface Treatment

Although the photocatalytic activities of the different facets of anatase TiO2 have been investigated extensively, controversies still abound in the photocatalytic orders of the facets. In the present work, we investigated the photocatalytic activity of different facets of anatase TiO2 treated with different surface treatment methods. The anatase TiO2 nanocrystals with {001} and {101} facets were synthesized by a hydrothermal method using hydrofluoric acid to control the ratio of different facets. The F similar to ions were removed by two methods: washing with NaOH aqueous solution or calcination. The photocatalytic activities of facets were characterized by dye degradation and the defects on the facets were investigated by X-ray photoelectron spectroscopy. Our results showed that different surface treatment methods could reverse the photocatalytic order of different facets. the calcination could enhance the density of oxygen vacancy on {001} facets and result in a photocatalytic order of {001} > {101}. In contrast, washing with NaOH aqueous solution produced inverse order.