Nitrogen-doped Titanium Dioxide Mixed Crystal Preparation And Catalytic Properties Of Visible Light,

TiO2 is actived only by irradiating with ultraviolet light due to its large band gap of 3.2eV. This suggests that TiO2 could utilize only a small portion (～5%) of the sun energy, compared to the visible region (45%), which seriously influences various industrial applications. Therefore, it has great significance to extend band gap response into the visible regime for pollutant elimination.In this paper, anatase-brookite mixed-crystal TiO2 materials using TiCl4 as titanium source by sol-gel technique are prepared in the beginning. Subsequently, N-doped anatase-rutile-brookite ternary mixed-crystal TiO2 nanoparticles (N-TiO2) are synthesized under solvothermal method. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), Ultraviolet-visible diffuse reflectance spectroscopy (UV-vis DRS) methods are employed to characterized the as-prepared photocatalysts for the elucidation of effects of crystal structure, surface morphology and photocatalytic performance.The results show:(1) The optimum preparation condition:molar ratio of TiCl4 and H2O (1:4), volume ratio of H2O and C3H8O (1:2), PEG-20000 as the surfactant, reaction temperature 80℃for 15h by so-gel technique. As a result, we get ultrafine and uniform TiO2 nanoparticles. Further, the optimum preparation condition of high photocatalytic performance N-doped TiO2 are:volume ratio of H2O and DMF (1:4), reaction temperature 120℃for 12h under solvothermal method.(2) Compared with the degradation ratio of undoped TiO2 and P25 for 5% and 9% separately, the results of photocatalytic degradation of methylthionine chloride demonstrate that the N-doped TiO2 catalyst exhibits the highest photocatalytic activity, reaching 90%. According to XRD and XPS analysis results, the phase composition of mixed-crystal and contents of nitrogen atoms have a significant effect for the performance of photocatalysts. The high photocatalytic activity is explained by the presence of junctions among different polymorphic TiO2 phase that enhance the separation of the photogenerated electron-hole pairs, hindering their recombination. Moreover, Nitrogen atoms are incorporated into TiO2 lattice and substitute a part of oxygen atoms, thus expanding the response range of light.(3) The dynamics of photocatalytic oxidation of methylthionine chloride with N-doped TiO2 agrees with Langmuir-Hinshelwood (L-H) model, and the reaction pertains to a first-order reaction. The reaction rate is controlled by reactant's concentration. The relation between reaction rate constant (k) and primary concentration of methylthionine chloride (co) is k∝c0-1.