CeO₂–Nb₂O₅ photocatalysts for degradation of organic pollutants in water

The photocatalytic properties of CeO₂–Nb₂O₅ photocatalysts in heterogeneous photocatalysis (under ultraviolet and visible radiation) and in Fenton-like process were reported. Methylene blue dye (MB) and phenol (Ph) were used as models of pollutant molecules for these reactions, and the photocatalysts were characterized by X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and thermally stimulated luminescence (TL). The results indicated that the addition of CeO₂ (0.3 wt%, 1.0 wt% and 2.0 wt%) to Nb₂O₅ sensitized the resultant materials, increasing light absorption in the visible region. However, there is a suitable formulation of CeO₂–Nb₂O₅ photocatalysts to improve each photocatalytic process. In heterogeneous photocatalysis, the addition of small CeO₂ quantities to Nb₂O₅ was enough to improve the photocatalytic activity of CeO₂–Nb₂O₅ photocatalysts (The best composition reported was CeO₂ 0.3 wt%.). The effectiveness of the catalyst was explained by the decrease in the number of trapping and luminescence centers in the conduction band of the material after the addition of CeO₂ to Nb₂O₅, but a large amount of CeO₂ decreased the number of trapping, luminescent and active centers to a large extent. Contrarily, in a Fenton-like process, the addition of CeO₂ to Nb₂O₅ was favorable in all the proportions studied. (The best composition was 2.0 wt% CeO₂.) In this case, the effectiveness was explained by the influence of the adsorption process (adsorption-triggered process), and the interactions between H₂O₂ and Ce³⁺ of the CeO₂ in each photocatalyst thus formed surface peroxide species O₂²⁻, which induced the removal of the organic molecules under visible light.