Structural and optical properties of sol-gel synthesized TiO2 nanocrystals: Effect of Ni and Cr (co) doping

Abstract

Nickel and chromium metal ions have been utilized to dope and co-dope titanium dioxide nanocrystals, thereby broadening the light absorption range of titania into the visible light spectrum. The doped and co-doped TiO2 nanocrystals were prepared using sol-gel techniques, with a varied doping concentration that extended from 0.25 to 10.0 wt.%.These modified materials underwent comprehensive analysis using standard analytical tools such as X-ray diffraction, Raman spectroscopy, BET surface area measurement, Fourier transform infrared spectroscopy, UV-vis diffuse reflectance spectroscopy, and fluorescence spectroscopy.The Powder XRD method uncovered that the reformed catalyst predominantly comprises the anatase polymorph, with the transition metal ion either taking the place of Ti or situated as interstitials in the TiO2 lattice. When metal ion concentration rose from 0.25 to 10 wt.%, Raman and UV-Vis absorption spectrums of the doped and co-doped catalyst exhibited a λmax shift towards a longer wavelength. Fourier Transform Infrared (FTIR) spectra revealed the stretching and vibrational behavior of hydroxyl radicals in the nanocrystals. The BET surface area of the doped and co-doped TiO2 nanocrystals significantly surpassed that of the undoped TiO2. Electronic structural studies of the TiO2, (Ti,Cr)O2, (Ti,Ni)O2, and (Ti,Ni,Cr)O2 crystals using density functional theory indicated a reduction in the band gap width (Eg) of pure TiO2 when doped with transition metals. Specifically, the indirect bandgap values for Ni(10%), Cr(10%) and NiCr(5%+5%) doping were 2.96, 2.83, and 2.7 eV, respectively. Furthermore, the photoluminescence intensity substantially decreased with the integration of transition metal ions in the TiO2 nanocrystals.