Characterization and photocatalytic activity of sepiolite-TiO2 and Na-montmorillonite-TiO2 catalysts

Abstract

This study focused on structural and photocatalytic properties of TiO2 incorporated Sepiolite and Na-Montmorillonite. Catalyst characterization was carried out by thermal gravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy with energy dispersive X-ray (SEM(EDX)), and scanning transmission electron microscopy (STEM). Photocatalytic activity was evaluated for β-Naphthol degradation in the presence of catalysts under UV irradiation. H2O2 and heat treatments did not enhance the photocatalytic activities of the catalysts. Alteration of titania-sol amount during the preparation of the catalysts, variation in Na+ ion concentration for the preparation of Na- Sepiolite-TiO2 and addition of Fe3+ ion to the Sepiolite-TiO2 and Na-Montmorillonite- TiO2, changed the structural characteristics and photocatalytic activities of the catalysts. For Sepiolite-TiO2 and Na-Montmorillonite-TiO2 catalysts, peak intensities of the clay minerals were found to decrease with the addition of titania-sol. Formation of TiO2 pillars is possible in Na-Montmorillonite-TiO2 catalysts due to the increments in the d-spacing values of the Na-Montmorillonite. At all conditions TiO2 was present as anatase crystallites. Change in Na+ ion concentration enhanced the anatase main peak intensities in Sepiolite-TiO2 catalysts, specifically for 3M Na-Sepiolite-TiO2 (100oC). EDX analysis indicated that 3M Na-Sepiolite-TiO2 (100oC) contains the highest TiO2 percentage. In the Fe-Sepiolite-TiO2 (500o) catalyst, height of the anatase peak decreased and the crystalline size increased. Fe-Na-Montmorillonite-TiO2 (500oC) showed lower anatase peak height compared to that of Na-Montmorillonite-TiO2 (500oC). For the photocatalytic degradation of the β-Naphthol, the best efficiency was obtained in the presence of Sepiolite-TiO2 (100oC). Lower degradation was obtained by use of Fe-Sepiolite-TiO2 due to the precipitation of iron hydroxide and formation of Fe2O3 on the TiO2 species. Presence of TiO2 pillars decreased the probobality of formation of Fe2O3 aggregates in Na- Montmorillonite-TiO2 and thereby increased the degradation yield.