The Effect Of Gd-N-P-Tridoping On The Performance Of TiO₂/SiO₂/NiFe₂O₄ Magnetic Nanocomposite Photocatalyst

To improve the solar utilization and the quantum efficiency of nano-TiO2,moreover to resolve it recovery problem in wastewater treatment, the magneticnano-composite photocatalyst with visible light response was developed byconstructing a core-shell nano-composite structure. It could offer novelhigh-performance photocatalytic materials for the treatment of water pollution with aphotocatalytic technique.Gd, N, P-tridoped anatase-TiO2 nano-sheets were successfully prepared by a sol-hydrothermal method from TiCl4 hydrolysis, using urea as nitrogen sources. Influences of Gd, N or/and P doping on physicochemical properties of TiO2 were investigated by X-ray diffraction, transmission electron microscopy, N2 physical adsorption-desorption, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, UV-vis absorbance spectroscopy, and photoluminescence spectroscopy techniques. Results showed that the optimal preparation conditions of Gd, N, P-tridoped sample were as follows: Gd-doping contents of 0.4 wt%, N-doping contents of 8.76 wt%, P-doping contents of 5 wt%, and calcined at 400 ℃ for 0.5 h. Doped P in TiO2 lattices played a predominant role in inhibiting phase transformation and crystal growth, as well as in improving surface textural properties of TiO2. Gd, N, P-tridoping inhibited recombination of photogenerated electrons and holes, increased surface hydroxyls, and improved UV absorption. GNPTO exhibited the enhanced photoactivity for 4-chlorophenol(4-CP) degradation under simulated sunlight irradiation as compared to undoped, single-doped, codoped, and commercial P25 TiO2. Removal rate of TOC reached 93.6% after irradiation for 120 min. Active species trapping experiments revealed that ?OH radical played a key role in 4-CP degradation, and photogenerated electron also played a minor role in 4-CP degradation. The synergetic mechanism of enhanced photoactivity for GNPTO was also discussed in detail.In addition, a sol-hydrothermal method without thermal treatment was successfully developed to obtain high-efficiency Gd, N, P-tridoped anatase-TiO2 nano-sheets using ammonia as nitrogen sources based on TiCl4 hydrolysis in aqueous solution. The structural performances of as-prepared samples were characterized by XRD, TEM, BET, degradation of 4-CP under simulated sunlight irradiation. Results indacated that the Gd-N-P-TiO2 presented the highest photoactivity with the apparent rated constant of 0.0678 min-1, which was 5.6 times that of P25 Ti O2(Kapp =0.0121 min-1). TOC removal rate for 4-CP solution(20 mg/L) in the presence of Gd-N-P-TiO2(0.8 g/L) reached 90% after 120 min irradiation, indicating that 4-CP was mineralized efficiently. Radical scavenging experiments indicated that ·OH in the solution was main reactive species. Enhanced photoactivity of Gd-N-P-TiO2 were attributed to synergetic effect of the increased UV light absorption ability, higher hydroxyl content, as well as improved surface textural properties.The magnetic nano-composite photocatalyst was developed by constructing a core-shell nano-composite structure. Super paramagnetism NiFe2O4 nanoparticles were prepared in a hydrothermal method. Then the nanoparticles were coated with a layer of SiO2 by NaSiO3 hydrolysis to prepare SiO2/NiFe2O4. By investigating calcination temperature, doping methods, pH value on the properties of TiO2/SiO2/NiFe2O4 nano-composite photocatalyst, the optimal preparation conditions of TiO2/SiO2/NiFe2O4 nano-composite photocatalyst were obtained. The photocatalytic activities of samples were evaluated by degradation of 4-CP under simulated sunlight irradiation. The influences of Gd-doping, P-doping, or Gd-N-P-tridoping on the properties of TiO2/SiO2/NiFe2O4 nano-composite photocatalysts were researched. Results indicated that Gd-doping, P-doping, or Gd-N-P-tridoping decreased the photocatalytic activity of TiO2/SiO2/NiFe2O4 nano-composite photocatalysts, and no effect on the magnetic was found.