Performance analysis of anomalous photocatalytic activity of Cr-doped TiO2 nanoparticles [Cr(x)TiO2(1-x)]

We report the synthesis and characterisation of pristine and chromium (Cr) metal ion-doped titanium dioxide nanoparticles [Cr(x)TiO2(1-x)] to study the anomalous effect of Cr doping on the photocatalytic property of TiO2. The presence of dopants generates more number of recombination pairs and increases surface coverage sites which decreases photocatalytic activity. We study the structural morphology of the synthesised Cr(x)TiO2(1-x) samples using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy analysis. The effect of Cr3+ ions on the optical properties of TiO2 has been studied using various imaging and spectroscopic techniques. Further, the effect of doping of Cr on the photocatalytic activity of TiO2 has been analysed in detail. The concentration of Cr in TiO2 has been chosen as 0, 1, 5 and 10% by weight. It has been observed that the pristine TiO2 exhibits better photocatalytic activity as compared to Cr-doped TiO2 irrespective of the Cr concentration. This can be attributed to the fact that due to Cr doping in TiO2, the number of available adsorption sites for malachite green reduces which degrades its photocatalytic activity. It is also confirmed by photoluminescence (PL) and time-resolved photoluminescence spectroscopy. PL intensity increases, and lifetime decreases with increase in doping concentration. Radiative recombination of electron and hole pairs of Cr3+ in TiO2 degrades its photocatalytic activity. The degradation efficiency is found to be 96% in the case of pristine TiO2 which reduces to 12% when doped with x = 10% concentration of chromium. Therefore, it is observed that in comparison with Cr-doped TiO2, pristine TiO2 exhibits an improved photocatalytic activity which shows the anomalous effect of Cr doping on the photocatalytic property of TiO2.