CaFe2O4 sensitized hierarchical TiO2 photo composite for hydrogen production under solar light irradiation

Abstract

Hierarchical spheres of self organized nanosheets of TiO2 are prepared by solvothermal method. The spheres comprising nanosheets are expected to exhibit high conducting properties. The present work is an attempt to explore the conducting properties of these spheres of TiO2 nanosheets that facilitate charge transfer and charge mobility. And at the same time to extend the absorption of TiO2 to visible light, it is combined with a low bandgap semiconductor CaFe2O4. In this perspective, CaFe2O4/TiO2 composite photocatalyst consisting of CaFe2O4 and TiO2 hierarchical spheres of nanosheets is prepared by solid state dispersion (SSD) method. The photocatalysts are characterized by thermo gravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 adsorption desorption, photoluminescence (PL) and UV-Vis diffuse reflectance spectra (DRS). SEM and TEM images show TiO2 spheres and the mesoporous structure is substantiated by the N2 adsorption desorption studies. UV-Vis DRS of the composites show visible light absorption confirming the sensitization of TiO2 by CaFe2O4. XRD shows the crystallinity of the prepared composites is anatase and SEM confirms that the TiO2 spheres are intact at 400°C calcination temperature. However, deformation of spheres is seen at higher temperatures. Photocatalytic activity of the composites is studied using methanol water mixtures and optimum conditions for hydrogen production are established. By comparing the activity of CaFe2O4/TiO2 composite under visible and solar light irradiation, the possible charge transfer processes that are responsible for the synergistic activity are visualized. Based on the results, a mechanism highlighting the structure activity correlation has been proposed.