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

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 . Powder XRD technique reveals that the modified catalyst majorly contains the anatase polymorph with the transition metal ion either substituting Ti or located as interstitials in the lattice of TiO 2 . Raman and UV–Vis absorption spectra of the doped and codoped catalyst a show λ max shift towards longer wavelength when in the metal ion concentration is increased from 0.25 to 10 wt%. FTIR patterns show the stretching and vibration patterns of hydroxyl radicals present in the nanocrystals. The BET surface areas of the doped and codoped TiO 2 nanocrystals have substantially higher surface areas compared with that of the undoped TiO 2 . Electronic structural studies of the TiO 2 , (Ti,Cr)O 2 , (Ti,Ni)O 2 , and (Ti,Ni,Cr)O 2 crystals using density functional theory indicated a reduction in the band gap width (E g ) of pure TiO 2 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 incorporation of transition metal ions in the TiO 2 nanocrystals. • Ni, Cr - codoped TiO 2 nanocrystals were fabricated by sol-gel technique. • When TiO2 doped with Ni and Cr, it stabilizes into an anatase polymorph. • Cr increases the visible absorption and leads to a lower band gap value. • Ni doped TiO2 lead to decrease the PL intensity of the titania nanocrystals. • Electronic properties of the TiO2, (Ti,Cr)O2, (Ti,Ni)O2, and (Ti,Ni,Cr)O2 crystals were evaluated using DFT calculations.