Photocatalytic activity of TiO2 doped with Zn2+ and V5+ transition metal ions: Influence of crystallite size and dopant electronic configuration on photocatalytic activity

Anatase TiO2 was prepared by sol–gel method through the hydrolysis of titanium tetrachloride and doped with transition metal ions like V5+ and Zn2+. The photocatalysts were characterized by various analytical techniques. Powder X-ray diffraction studies revealed only anatase phase for the doped samples. The band gap absorption for the doped samples showed red shift to the visible region (∼456 nm) as confirmed by UV–vis absorption spectroscopy and diffuse reflectance spectral studies. The surface area of the Zn2+ doped samples were higher than the V5+ doped samples as observed by BET surface area measurements due to their smaller crystallite size. Scanning electron microscopy showed almost similar morphology, while energy dispersive X-ray analysis confirmed the presence of dopant in the TiO2 matrix. The photocatalytic activities of these catalysts were tested for the degradation of Congo Red under solar light. Although both the doped samples showed similar red shift in the band gap, Zn2+ (0.06 at.%) doped TiO2 showed enhanced activity and its efficiency was five fold higher compared to Degussa P-25 TiO2. This enhanced activity was attributed to smaller crystallite size and larger surface area. Further completely filled stable electronic configuration (d10) of Zn2+ shallowly traps the charge carriers and detraps the same to the surface adsorbed species thereby accelerating the interfacial charge transfer process.