Preparation Of Nano-zinc Oxide, Doped And Performance

In this dissertation,ZnO nanoparticles,ZnO nanorods,Ti(Sn)-doped ZnO nanorods and ZnO-SnO₂ composite oxides have been synthesized, respectively,of which properties have been characterized.The details are presented as follows.Firstly,ZnO nanoparticles can be precipitated by treating ZnO sol via four methods,which have been synthesized during a sol-gel synthesis. XRD and TEM have been employed to characterize the as-prepared samples,and their photocatalytic properties were investigated.The results show that ZnO nanoparticles,precipitated by sonicating the colloidal ZnO solution,adding water to the colloidal ZnO solution and then boiling it, adding heptane to the colloidal ZnO solution,and evaporating part solvent of the colloidal ZnO solution,have particle diameters of 6.2±1.5 nm,7.4±2.6 nm,4.6±1.5 nm and 6.6±1.9 nm.The agglomeration situation for the sample precipitated by sonicating the colloidal ZnO solution is the least,and that for the sample precipitated by adding water to the colloidal ZnO solution and then boiling it is the most serious,the sample precipitated by adding heptane to the colloidal ZnO solution has higher photocatalytic activity,and its degradation rate of methyl orange is 91.1%.Secondly,ZnO nanorods were synthesized by alcoholthermal method.XRD and TEM have been employed to characterize the as-prepared samples.The results show that the sizes of the samples increase with prolonging the reaction times.And the hydrolysis of zinc acetate can be controlled well through adding H₂O to obtain longer ZnO nanorods.Photoluminescence spectra of the ZnO nanorods were measured at room temperature,and three emitting bands,being a violet emission at 413 nm,a blue band at 450-470 nm and a green band at around 525 nm,were detected.Thirdly,Ti and Sn-doped ZnO nanorods with various doping concentrations were synthesized by alcoholthermal method.The as-synthesized samples were characterized with XRD,TEM,HRTEM and EDS,of which the Photoluminescence spectra were measured at room temperature.The results show that after doping Ti or Sn,the reflections recorded can be readily indexed to hexagonal ZnO(JCPDS 36-1451).The intensities of diffraction peaks decline with the increase of doping concentration,showing the degradation of crystallinity.After doping Ti,the morphology of ZnO nanorods keep almost the same as the pure ZnO nanorods.With increasing the doping concentration,the morphology of Sn-doped ZnO varies from long nanorods to fat and short ones,further to short columns.Photoluminescence spectra of the Ti-doped ZnO nanorods includes three emitting bands,being a violet emission at 400-415 nm,a blue band at 450-470 nm and a green band at around 550 nm.The emission intensities of the Ti-doped ZnO nanorods enhance gradually with increasing the doping concentrations.As to the Sn-doped ZnO nanorods,the green emission shifts to 540 nm,and the emission intensities increase first but decrease later with increasing the doping concentrations.Fourthly,ZnO-SnO₂ composite oxides have been synthesized at different calcination temperatures via co-precipitation method.XRD, TEM,SEM and BET were employed to characterize the as-prepared samples,and their photocatalytic properties were investigated.The results show that the phase composition and crystalline state of the samples are different with molar ratios of Sn:Zn and calcining temperatures. Calcination temperature has an great effect on the shape and size of the samples.The samples calcined at 600℃,700℃and 800℃are uniform spherical particles with good dispersion,cubes with edge length of about 200-300nm,and spherical particles and cubes with the diameter and edge length of up to 1μm.The sample has the highest activity when the molar ratio of Zn to Sn is 2:1 and the calcination temperature is 700℃.