Zhao Xueguo, Wang Yanxiang, Li Jiake

(Jingdezhen Ceramic University, National Research Center for Domestic and Building Ceramics,

Jingdezhen 333403, Jiangxi, China)

Extended abstract:

[Background and purposes] The applications of TiO₂ has been limited in the field of photocatalysts, due its large energy gap. Although N doping can be used to enhance the photocatalytic degradation efficiency of TiO₂, further research is needed to confirm the effect of N doping site and level on the photocatalytic evolution of H2. MgCO₃/C-N-TiO₂ photocatalysts with high N doping concentrations were synthesized by using solvothermal method assisted with heat treatment. It was found that interstitial C and substitutial N were incorporated into the lattice of TiO₂. Meanwhile, the C-N codoping efficiently narrowed the band gap (~1.5 eV) of TiO₂, while MgCO₃ on the surface of TiO₂ with high dispersion improved the separation of photoinduced carriers.

[Methods] MgCO₃/C-N-TiO₂ photocatalysts with high N concentrations were synthesized by using solvothermal method assisted with heat treatment. TiCl4 and Mg3N2 powder with designed quantities were added to 200 mL toluene. The molar ratio of N/Ti ions is 0.1–0.4. The mixture was then heated for 12 h at 200 ℃ using a Teflon-lined stainless autoclave. The products were hydrolyzed with 0.1 mol·L−1 NH₄HCO₃ solution and washed several times using deionized water and ethanol. They were then dried at 80 ℃ for 24 h. The produced samples were calcined for 0.5 h at 400 ℃ in air atmosphere. Phase composition of the powders was analyzed by using DMAX-RB X-ray powder diffractometer (Cu-Kα radiation, λ=0.154 nm). The step size was 0.02° and the scanning range of 2θ was 10°–70°. Microstructure and selected area electron diffraction (SAED) of the samples were studied by using JEM-2010 transmission electron microscope (TEM). Excitation spectrum (PLE spectrum) and emission spectrum (PL spectrum) of the products were obtained by using F-7000 fluorescence spectrometer, where the slit width of the excitation and emission windows was set to be 1 nm.

[Results] XRD peaks of the MgCO₃/C-N-TiO₂ are in good agreement with those of the standard data, while N doping has significant effect on crystal structure of TiO₂. When the molar ratio of N/Ti exceeds 0.2, the TiO₂ was varied from anatase to rutile. In addition, no MgCO₃ peaks are observed, owing to its content below the XRD detection limit. In the MgCO₃/C-N-TiO₂ powders, MgCO₃ is well dispersed on the surface of TiO₂ particles. XPS analysis results indicated that N was incorporated into the crystal structure of TiO2. The absorption spectra of TiO₂ and MgCO₃/C-N-TiO₂ samples indicate that MgCO₃/C-N-TiO₂ has stronger visible light absorption than that of TiO₂, leading to higher photocatalytic hydrogen production performance of MgCO₃/C-N-TiO₂.

[Conclusions] MgCO₃/C-N-TiO₂ photocatalysts with high N doping concentrations were synthesized by using a solvothermal method assisted with heat treatment. The interstitial C and substitutial N were incorporated into the lattice of TiO₂. The C-N codoping efficiently narrowed the band gap (~1.5 eV) of TiO₂, while the highly dispersed MgCO₃ on the surface of TiO₂ improved the separation of photoinduced carries. When the content of MgCO3 was 3 wt.%, the stable average H₂ evolution rate was about 3000 µmol·g−1·h−1. under 300 W Xe lamp irradiation.

Key words: photocatalysts; TiO₂; dopant; heterojunction; photocatalytic hydrogen evolution