An investigation of transition metal doped TiO2 photocatalysts for the enhanced photocatalytic decoloration of methylene blue dye under visible light irradiation

Abstract

Photocatalytic decolouration of dyes/pollutants using semiconducting materials has grabbed great attention in recent days. The current study focuses on a sol-gel method for preparing semiconducting materials such as TiO2 (titanium oxide) and transition metal (Zn, Zr, Cu) doped TiO2, which were characterized by X-ray Powder Diffraction (XRD), Scanning Electron Microscopy (SEM), UV–visible Diffuse Reflectance Spectroscopy (DRS) and UV–visible spectrophotometer, respectively. The photocatalytic behaviour of samples was tested with Methylene blue (MB) dye by observing the decolouration of the MB dye in aqueous solutions under visible light irradiation. The UV-DRS spectra showed that Zn doped TiO2 demonstrated a better photocatalytic efficiency than TiO2 and Zr, Cu doped TiO2 catalysts. The effect of Zn doped TiO2 has a lesser band gap would probably lead to enhance the MB dye degradation in aqueous solutions under visible light irradiation compared to TiO2 and Zr, Cu doped TiO2 catalysts. UV–vis spectrum varied with the irradiation time between 10 and 60 min and the concentration of MB decreased with the increasing irradiation time. UV–vis study revealed that the Zn (0.01) doped TiO2 exhibited 99.64% MB decolouration as compared to 90.4% by pure TiO2. The absorbance spectrum of Zn doped TiO2 exhibited the lighter harvest in the visible light region, which facilitated more light energy for the utilization of the photocatalytic activity for the decoloration of MB. Zn doped TiO2 catalyst exhibited a greater photocatalytic activity than pure TiO2 and the other metal doped TiO2 catalysts.