Photochemical reactivity of apical oxygen in KSr(2)Nb(5)O(15) materials for environmental remediation under UV irradiation

Abstract

The photocatalytic activity of a series of novel KSr₂Nb₅O₁₅ materials was studied using the photooxidation of methylene blue as model reaction. The influence of the calcination time upon the crystalline structure and photoactivity was verified. Characterization was performed by XRD, SEM, FTIR, UV-Vis/DR, Helium picnometry, and N₂ and CO₂ adsorption-desorption isotherms. The diffraction line profile and the refinement of the structural parameters of KSr₂Nb₅O₁₅ were obtained from the XRD patterns by the Rietveld method. Data showed that samples were photoactive under UV irradiation, regardless the synthesis conditions. However, the calcination time had a clear influence upon the photocatalytic activity of the samples, being more efficient towards the degradation of the dye those obtained at a lower calcination time. Indeed, the sample calcined for 4h showed up to 4 times higher photocatalytic activity than commercial TiO₂. Additionally, a correlation between the photocatalytic activity and the displacement of the Nb ion from the central position in the [NbO₆] octahedron was found. It is suggested that this fact causes an important polarization of the niobate structure. The apical oxygen in these samples is very reactive and can lead to the formation of superoxoradical anions (O₂^-) showing that KSr₂Nb₅O₁₅ can be potentially used in photocatalytic reactions under UV irradiation.

Keywords: Methylene blue; Niobate-based materials; Photocatalysis; Structural refinements.