Study On The Photocatalytic Performance Of ZnO Powder With Cu/Ce Doping And ZnTPP Sensitizing

In recent years, metal oxides have attracted a lot of attention for their ability in the photocatalytic degradation of organic pollutants, among which zinc oxide（ZnO） and titanium dioxide（TiO2） semiconductor materials are much more in favored. In this thesis, the pure ZnO and Cu/Ce: ZnO prepared by sol-gel methods, as well as the Zinc porphyrin（Zn TPP）-ZnO prepared by impregnation methods had been chosen as the research object, with X-ray Diffraction（XRD）, Electron Paramagnetic Resonance（EPR） and Transmission Electron Microscopy（TEM） techniques being utilized to characterize the surface morphology, crystal types and structures, as well as free radical kinds and contents of the powder samples. By using methyl orange as the simulated pollutant, sunlight as the illuminant for Cu/Ce-ZnO materials, a 300 W lamp group as the simulated solar light for Zn TPP-ZnO materials, we used Ultraviolet-Visible Spectroscopy（UV-Vis） technology to analyze the photocatalytic activity of the samples. The main results are as follows:1. Through the preparation process of pure ZnO powder by Sol-gel method, the effect of magnetic stirring temperature, drying time, as well as calcination temperature on the produce of ZnO grain crystallinity and size had been studied. Ultimately, the optimal conditions for preparing was determined: solution concentration of Zn²⁺(Cu²⁺/Ce³⁺ and Zn²⁺) was 0.6mol/L, with the constant magnetic stirring temperature of 50℃（stirring for 1h）, quiescence for 24 h, the blast drying temperature of 90℃（for 10h） and calcination temperature of 500℃.2. Doping with appropriate amount of transition metal Cu and rare metal Ce could effectively improve the photocatalytic activity of ZnO materials. When the doping concentration of Cu²⁺/Ce³⁺ was 0.5%, 1%, 2%, 4%, 8%, with the doping amount of 2%, the degradation rate to methyl orange reached to the maximum, which were 37% and 38% respectively and were comparatively increased 12% and 13% than the pure ZnO. The XRD results showed that CuO and Cu₂O emerged after Cu-doping, while CeO₂ was generated after Ce-doping. Doping with Cu and Ce both had refinement effect on ZnO particles, with the grain size decreased first and then increased as the increasing dopant concentration. Totally three kinds of free radical signal could be seen in the EPR spectrum of ZnO, with the g factor being 1.954, 1.997 and 2.07 respectively, which belonged to Zn-H complex, oxygen vacancy plus and Cu²⁺. The change of resonance signal under the three different concentrations showed that the patterns of Cu²⁺ getting into the ZnO lattice were orderly succession of the Zn atom, filling Zn vacancy and interstitial Cu atom, with the increase of the concentration of Cu-doping. According to the EPR spectrum of Ce: ZnO, in addition to the signal nearly to g=1.954 and g=1.997, there was a new resonance signal at g=2.016, which was caused by the adsorption of superoxide ions on the surface of CeO₂.3. Zn TPP with different quality had been loaded in the preparation process of ZnO powder through impregnation methods, with the mixing temperature, light irradiation time and the effect of loading capacity（2μmol、4μmol、6μmol、8μmol、10μmol） on photocatalytic activity of ZnO had been studied. UV-Vis and TEM techniques had been adopted to analyze the Zn TPP-ZnO composite powders. As a result, photocatalytic activity of the composite catalyst was the highest when stirring at normal temperature, lighting to 1h and the loading of 6μmol. Moreover, Zn TPP was loaded on the ZnO particles surface in the way of absorbing, which played a role to generated and transferred motivated electrons in photocatalytic effect.