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On the excitation mechanism of visible responsible Er-TiO2 system proved by experimental and theoretical investigations for boosting photocatalytic activity

Abstract:

One of the challenges in the field of heterogeneous photocatalysis is the development of new type of photoactive materials activated by low-power and low-cost irradiation sources, and to understand the mechanism of photocatalytic reaction in the presence of those materials. Photocatalysis based on Er-TiO<inf>2</inf> has become an attractive process to remove contaminants from aquatic environments. Unfortunately, there is no available literature presenting the systematic experimental and theoretical study of the effects of erbium ions on the photocatalytic activity of TiO<inf>2</inf> and visible light excitation mechanism of this system. Accordingly, to obtain solar-responsive photocatalysts, nanostructured Er-TiO<inf>2</inf> was prepared via hydrothermal method. The physicochemical characterization of samples indicate that modified photocatalysts contain both doped erbium and the surface adsorbed erbium species (e.g., Er<inf>2</inf>O<inf>3</inf>, Er(OH)<inf>x</inf>). Predicted electronic structures of Er-doped TiO<inf>2</inf> indicate that the formation of new Er-4f states within the band gap region of TiO<inf>2</inf> might be crucial for observed photocatalytic effects towards Vis response. However, the up-conversion process is not responsible for Vis activity and efficient O<inf>2</inf><sup>[rad]−</sup> generation. Moreover, Er modification of TiO<inf>2</inf> results in an inhibition of the growth of titania crystallites, and thus an increase in the specific surface area, which are also beneficial for an efficient degradation of pollutants.