Synthesis And Photocatalytic Activity Of Nanometer Zinc Oxide And Tin Doped Zinc Oxide

According Pollution, especially water and air pollution which has become a threat to mankind, has accompanied the continual progress in science and technology. Therefore, the purification of air and water is of upmost importance. Photocatalytic technology an excellent water purification technology which possess several advantages such as simple operation, mild operating conditions and being non-toxic. The study of photocatalysis began in the early 1970 s when Professor Fujishima and Honda discovered the photolysis of water on TiO2 electrodes. Due to its relatively high photocatalytic efficiency and low cost, TiO2 is widely studied as the catalyst for photocatalysis. As compared to TiO2, ZnO possesses similar band gap of 3.2 eV, high quantum efficiency and a larger absorption bandwidth which would enhance the photocatalytic performance. Different methods were explored for the preparation of intrinsic ZnO nanoparticles and Sn doped ZnO nano powders. The structure, morphology of and photocatalytic properties of these synthesized materials were characterized by XRD, SEM, TEM, XPS, PL, UV-Vis and PL. The thesis mainly includes the following contents.1、Nano ZnO powders were prepared by the sol gel method and the influence of calcination temperature and different stabilizers(monoethanolamine, two ethanol, triethanolamine) on the crystallization process of nano ZnO powders were studied. The structure, morphology and optical properties of the ZnO particles were characterized by XRD, SEM, TEM, XPS, PL, UV-Vis and FTIR. Results show that the ZnO particles are spherical, uniformly distributed, about 10-50 nm in size and also possess the wurtzite structure. The particles cluster together when the calcination temperature is low and scatter and crystallize when the temperature increases. A broad peak situated in between 375-550 nm could be observed from the PL spectra. The degradation of methyl orange, methylene blue and Rhodamine B under UV irradiation is tested. 100% degradation is eventually achieved and the degradation conforms to the first-order kinetic model. The effects of different calcination temperatures and different stabilizers on the photocatalytic degradation rate are discussed based on the test results.2、Nano ZnO powders were prepared by the polyacrylamide gel method and the dry gels were calcinated at different temperatures to obtain the final samples. The structure, morphology and optical properties of ZnO particles were characterized by XRD, TEM, XPS, PL, UV-Vis and FTIR. Results show that samples prepared by this method exhibited high uniformity and the crystallinity increases with the increase of the calcination temperature. Spectral analysis showed that the defect concentration of the samples differ with different calcination temperature. Under UV irradiation, it was discovered that the highest degradation efficiency of the simulated pollutants was achieved when the sample was calcinated at 650C; this is in stark contrast to the samples prepared by the sol gel method. Comparison of the two methods show that particles prepared by the polymer network gel method exhibit higher uniformity, better light absorption, easier production of hydroxyl radicals and other oxidant molecules as well as higher efficiency of photocatalytic degradation of pollutants.3、Sn doped ZnO powders were prepared by an improved polymer network gel method, with the appropriate calcination temperature being selected by the analysis of the calcination temperature in section 2. The influence of doping concentration on the photocatalytic effect was studied. Through experimental analysis, it was discovered that the best photocatalytic effect was achieved when the samples were doped with 1% of Sn; the MO solution was almost completely degraded in 200 min under UV irradiation. Characterization of the samples showed that the morphology of ZnO nano powder was almost not affected by the doping of Sn. Through XPS, PL and UV-Vis analysis, it was determined that the 1% Sn doped sample contained a high concentration of oxygen vacancies, strong absorption in the UV region and fastest generation rate of electron-hole pairs. The combination of these aspects results in the best photocatalytic effect.