High-pressure Synthesis Of Titanium Dioxide Metastable Phase And Study Of Its Photoelectric Properties

The environment human beings lives by is being seriously polluted.People are trying to find an effective way to degrade pollutants.TiO₂ can exhibit catalytic activity under irradiation of natural light and degrade the pollutants to non-toxic small molecules.With the advantage of non-toxicity and reusability,TiO₂ has been widely studied by the researchers.However,TiO₂ can only be excited by the ultraviolet part of the sunlight due to its wide band gap.In order to enhance the utilization rate of the sunlight,researchers have done much work.When proceeded under high pressure and high temperature,the atom and electron arrangement of the TiO₂ changes and then TiO₂ forms new phases,which could totally vary in the physical and chemical properties.If it is supposed that the parent phase is anatase,when proceeded under high pressure and high temperature,anatase undergoes a series of phase transition as anatase phase,columbite phase,baddeleyite phase,an unknown cubic phase,and cotunnite phase.We studied the enthalpy of these phases with the First-principle software CASTEP and then we plotted the enthalpy-pressure curve to find the structure with optimal enthalpy at various pressures.We also explored the elastic constants and phonon scattering spectra of these metastable phases to check the mechanical and dynamic stability of the structure.At last,we studied the band structure and light absorption spectrum of the columbite and baddeleyite phase.In the experiment section,we respectively processed micron anatase and nano anatase on this condition of the high-temperature and high-pressure produced by a homebred cubic press.The micron anatase can’t be transformed into columbite phase completely but a mixture which contains rutile phase,anatase phase and columbite phase.The nano anatase was transformed to columbite phase completely when dealt in the same conditions.We also mixed nano anatase with nano black carbon in a certain proportion,and processed the mixture on the condition of high pressure and high temperature.Then we got“black columbite”.It can be seen from the X-ray diffraction spectrum that the resultant product is still the columbite phase TiO₂,but the peak position shifts slightly to a high angle,demonstrating that a small part of the oxygen atoms in the crystal lattice are reduced.