Controllable Synthesis, Characterization And Photocatalytic Properties Of ZnO Nanomaterials

ZnO, a common wide-band-gap semiconductor, has great application prospect inphotocatalyst, solar cells, gas sensors, nanogenerators owing to its outstanding opticaland electrical properties. It has been found that the properties of nanomaterials aredetermined by their morphologies, shapes and sizes. Therefore, controllable synthesisof ZnO nanomaterials with different morphologies, which can change or improve theirproperties to some extent, is significantly important in view of both fundamentalresearch and practical applications, and has stimulated intensive research interest.This thesis carried out preliminary exploratory research on the controllable synthesisand application of ZnO nanomaterials. The main results are as follows:(1) Hierarchical porous ZnO microspheres were successfully synthesized bycalcining the microspheric zinc hydroxide carbonate precursor, which were theprecipitate products by using zinc nitrate hexahydrate, urea and trisodium citrate asthe starting materials. The products were characterized by XRD, SEM, TEM, UV-vis,FTIR, et al. SEM and TEM images showed that the hierarchical porous ZnOmicrospheres with diameter of4-5μm, were constructed by numerous ultrathinnanosheets which were embedded by many irregular pores and had a well-crystallinestructure. BET analysis showed that the specific surface area of the ZnO microsphereswas39.6m2/g and most of the pores fell into a size range of20-60nm. The influencesof concentrations of urea and trisodium citrate and reaction time on the morphologiesof the products were systematically studied. It was found that trisodium citrate playeda key role in determining the spherical morphology. On the basis of experimentalresults, a possible formation mechanism of the hierarchical porous ZnO microsphereswas proposed.(2) The photocatalytic activity of porous ZnO microspheres was investigated byphotodegradation of methylene blue under ultraviolet irradiation. The photocatalyticresults revealed that the methylene blue solution with an initial concentration of1.0×10–5mol/L was totally photodegraded by the porous ZnO microspheres after80minirradiation. The as-prepared ZnO microsperes exhibited a significantly enhancedphotocatalytic activity than commercial ZnO and TiO2. This was mainly attributed tothe special structural feature of porous ZnO microspheres.(3) Grenade-like ZnO nanostructures were synthesised by a facile solvothermalroute in a mixed solvent made of ethylene glycol and water. The products were characterized by XRD, SEM, TEM and PL. Grenade-liked ZnO nanostructures, withlengths of6.4μm, were composed of tow nanorods with different sizes. The nanorodshad a single-srystal hexahonal structure and grew along the (0001) direction. The PLspectrum of the grenade-like ZnO showed a strong UV emission peak. The influencesof volume ratio of ethylene glycol and water on the morphologies of the productswere studied. It was found that the bydroxyl groups of ethylene glycol absorbed onthe positive polar plane of ZnO by coulomb interaction and restarded the growthalong (0001) direction.