The crucial role of W6+, P5+ and N3- dopant ions in the anatase TiO2 crystal lattice for enhanced photocatalytic activity under the irradiation of UV/solar light: Structure-reactivity correlation

A simple sol-gel route was adopted for the preparation of TiO2 and W6+ (0.02 at. %) doped TiO2. The prepared samples were annealed at 500 degrees C (WT500) and also at 700 degrees C (WT700). Powder X-ray diffraction (PXRD) study confirms the anatase structure for TiO2 and WT500 samples, whereas WT700 contains both anatase and rutile phases of TiO2. Doping of P5+ (0.5 and 1.5 at. %) and N3- (0.2 at. %) ions into the anatase lattice structure of WT500 sample was done by wet impregnation method to get 0.5PWT500, 1.5PWT500, PWNT500, 0.5PWT900 and 1.5PWT900 catalyst samples which were annealed at 500 degrees C and 900 degrees C. P5+ dopant could effectively inhibit the phase transition of 0.5PWT900 sample from anatase to rutile, which otherwise takes place in the case of WT700 at 700 degrees C. Formation of titanium pyrophosphate (TiP2O7) was confirmed along with anatase TiO2 for 0.5PWT900 sample. The number of PXRD peaks pertaining to TiP2O7 and their intensities increased with the increase in H3PO4 concentration and the calcination temperature. X-ray photoelectron spectroscopic technique (XPS) has confirmed the oxidation states of dopant ions as W6+, P5+ and N3-. The photocatalytic activities of all the above catalysts were studied for the degradation of congo red (CR) dye as the model pollutant under UV/solar light irradiation. The tridoped PWNT500 catalyst showed higher efficiency due to the synergistic effects of dopants. An attempt is made in the present research to correlate the structure of the catalyst with the photo-catalytic reactivity.