Doping Behavior of Zr⁴⁺ Ions in Zr⁴⁺-Doped TiO₂ Nanoparticles

TiO₂ nanoparticles doped with different concentrations of Zr⁴⁺ ions were prepared by the sol–gel method and annealed at different temperatures. X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and high resolution transmission electron microscopy (HRTEM) techniques were used to investigate the existing states and doping mechanism of dopants as well as the phase transition of the Zr⁴⁺-doped TiO₂ samples. It was revealed that the doping behavior of introduced Zr⁴⁺ ions was closely related to the doping concentration. The Zr⁴⁺ ions would replace the lattice Ti⁴⁺ ions directly in substitutional mode at a certain annealing temperature. Moreover, if the concentration of doped Zr⁴⁺ ions is high enough, excess Zr⁴⁺ ions would form ZrTiO₄ on the surface of TiO₂. In addition, the phase transition temperature from anatase to rutile increases significantly after doping Zr⁴⁺ ions, due to their larger electropositivity and radius than those of Ti⁴⁺ ions. Our results may afford a better understanding on the doping mechanism and aid in the preparation of Zr-doped TiO₂ with high photoelectric performance

The Design of TiO₂ Nanostructures (Nanoparticle, Nanotube, and Nanosheet) and Their Photocatalytic Activity

Density functional theory (DFT) calculation is carried out to access the band structure and density of states (DOS) based on the models of TiO₂ nanoparticle, nanotube, and nanosheet, predicting the order of the photocatalytic activity for three different nanostructures. Sol–gel method and hydrothermal method are used to achieve desired morphologies: nanoparticles, nanotubes, and nanosheets (fragmentized nanotubes). The photocatalytic activity ranks in the order of nanosheets > nanotubes > nanoparticles, which is consistent with theoretical prediction. It was revealed that the enlargement of band gap is caused by the quantum confinement effect; the prolonged lifetime of photogenerated electrons and increased specific surface areas are dependent on the morphology of the nanostructure. All these factors contribute to the improvement of the photocatalytic activity for nanostructures. Our results can guide the design and selection of low-dimensional nanomaterials with desired morphology and improved photoelectric functional properties, which can be used in many fields, such as solar cells, photocatalysis, and photosynthesis