Synthesis, Photocatalytic Activity And First-Principle Calculations On Electronic Structure Of Nitrogen-Doped ZnO And ZnO /Ag Nanomaterials

The precursors of ZnO and ZnO/Ag nanocomposites were synthesized by the precipitation method with ZnSO4 and AgNO3 as the starting material and NH4HCO3 as the precipitation, and then the ZnO nanomaterials and ZnO/Ag nanocomposites were prepared by centrifuge, drying and calcination of the precursors. Then the precursors were doped by different nitriding methods. The morphology, structure and contents of N-doped of the samples were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) and Vario ELIII analyzer. The effects of the synthetic technology for N-doped on the photocatalytic activities of the ZnO and ZnO/Ag nanocomposites were studied, while the optimized N-doped reaction technics were obtained. In addition, the computer program FULLPROF which based on the principle of Rietveld method was used to the refined the crystal structure of the N-doped ZnO/Ag nanocomposites. The band structure and density of states of the doped and un-doped samples had been calculated in the frame of density functional theory (DFT) using the CASTEP code. The theoretical investigations were employed for better understanding the enhanced photocatalytic activity for the samples. The main research contents as follows:(1) N-doped ZnO nanomaterials were successfully prepared by plasma nitriding technology under the tempretures of 350℃, 400℃and 450℃, respectively. The photocatalytic studies suggested that all the N-doped ZnO nanomaterials exhibited highter photocatalytic under the simulated sunlight. N-doped ZnO which prepared by the plasma nitriding technology under 400℃had the highest photocatalytic activity. During the exposure to simulated sunlight for 6h, methyl orange aqueous solution degradation efficiency is about 83.18% for. The XRD result showed that the products were consisted of only hexagonal wurtzite structure of ZnO and the average diameter of N-doped ZnO was about 20nm.N-doped ZnO nanomaterials were successfully prepared by atmosphere nitriding method under the different tempretures (370℃,380℃,390℃,400℃) and different dosages rate of raw materials (m(ZnO):m(C3H6N6)= 1:1,1:1.5,1:2,1:2.5,1:3). The morphology, structure and the effects of the technics on the photocatalytic activities for N-doped ZnO nanomaterials had been studied. The optimized N-doped reaction technics as follow: the atmosphere nitriding temperature was 380℃and the dosages rate of raw materials was 1:2. Under the optimization synthesis conditions, the average diameter of N-doped ZnO was about 25nm, and the nitrogen content was 3.84%. The XRD result showed that the products were only consisted of hexagonal wurtzite structure of ZnO, and no new phase was produced, which indicates that some N atoms entered into the lattice of ZnO and replaced O atoms. The photocatalytic property of N-doped ZnO nanomaterials was examined under simulated sunlight, and the degradation ratio of methyl orange solutions was 85.36% after 6h.(2) N-doped ZnO/Ag nanocomposites were successfully prepared by atmosphere nitriding method under the different tempretures (360℃,370℃,380℃,390℃,400℃,410℃) and different dosages rate of raw materials (m(ZnO/Ag):m(C3H6N6)= 1:1,1:1.5,1:2,1:2.5,1:3). The morphology, structure and the effects of the technological parameter on the photocatalytic activities for N-doped ZnO/Ag nanocomposites had been studied. The optimized N-doped reaction technics as follow: the atmosphere nitriding temperature was 390℃and the dosages rate of raw materials was 1:2. Under the optimization synthesis conditions, the average diameter of N-doped ZnO was about 25nm, and the nitrogen content was 9.97%. The XRD result showed that the products were consisted of hexagonal wurtzite structure of ZnO and metallic Ag, and there was no new phase was produced, which indicates that some N atoms entered into the lattice of ZnO and replaced O atoms. Rietveld refinement results showed that lattice parameters of ZnO and Ag had slightly decreases. The photocatalytic property of N-doped ZnO/Ag nanocomposites was examined under simulated sunlight, and the degradation ratio of methyl orange solutions was 99.97% after 2h.3) The band structure and density of states (DOS) of the doped and un-doped samples had been calculated in the frame of DFT using the CASTEP code. The results showed that band gap of the N-doped ZnO reduce by about 0.15eV compared to un-doped ZnO. In addition, Zn 3d states spread to the upper level with dispersion for N-doped nanocomposites. In this situation, the Fermi level shifts to the valence band and a narrow-deep acceptor level formed in the energy gap after N doping and the transition of an electron from valence band to conduction band will need less energy in N-doped nanomaterials which demonstrated the mechanism for the enhanced photocatalytic activities of N-doped nanomaterials.