Low-temperature Synthesis And Their Photocatalytic Properties Of ZnO Nanostructure

Semiconductor nanomaterials have become a hotspot in research of nanometer materials in the world because of their unique optical, electrical, mechanical properties and their potential application. Domestic and foreign researchers have been exploring hard unremitting in order to discover new peculiar physical and chemical properties of nanomaterials and find their appropriate application. There are many methods with own advantages reported for preparing nanomaterials at present, but there are also some shortcomings, and some difficulties to obtain the nanomaterials of novel morphology with controllable morphologies and sizes. Because nano ZnO has potential application in photocatalysis, solar cells, sensing nanometer power, room temperature ultraviolet light, therefore, based on the excellent physical and chemical properties of nanometer ZnO as the research object, low temperature synthesis and characterization of ZnO nanostructure with the special morphology were be carried out, on this basis, the relationship between the nano ZnO structure, morphology and doping and its photocatalytic performance were further investigated.Firstly, using Zn（AC）₂ and NaOH as raw materials, ZnO with flower-like structure was prepared successfully by a microwave hydrothermal method in the presence of the cationic surfactant of cetyltrimethylammonium bromide（CTAB）. When the reaction was performed in the absence of CTAB, rod-like microstructures are obtained; when 0.2 M CTAB was added to the reaction solution, the flower-like microstructures were obtained because the spherical micelle was correspondingly formed as a soft template; When the mole concentration was increased to 0.5 M, only rod-like microstructures were obtained because CTAB aggregation in aqueous solution will form rod-like micelle. The photocatalytic activities of the synthesized flower-like microstructure were evaluated by the degradation of methylene orange（MO）, and the results had shown that the synthesized products presented superior decolorization efficiency.Secondly, using zinc acetate and cobalt acetate as raw materials, ethanol and polyvinypyrrolidone as the solvent and complexing agent, Co-doped ZnO nanofibers were successfully prepared by simple electrospinning method. Co-doped ZnO nanofibers had shown good uniformity, and its diameter with narrow distribution range was about 100 nm. In addition, its photoluminescence properties were also studied, and the results had shown that PL spectra of Co-doped ZnO nanofibers exhibitted a strong near band-edge emission at 385 nm. Compared with the pure ZnO nanofibers, the slight red-shift of the band-gap edge was attributed to narrowing of the width of band gap due to Co doping. The photocatalytic activity of Co-doped ZnO nanofibers in aqueous solution under UV light irradiation shown that it had very high degradation level for MO. After 80 min, its photocatalytic degradation rate could reach 93%.Then, Flower-like ZnO nanostructures had been successfully synthesized via sonochemical method, only with zinc acetate and potassium hydroxide as reactant. The growth mechanism of the flower-like ZnO nanostructure was discussed by studing the change of the structure and morphology of the product with the different ultrasonic time. At the beginning of the ultrasonic chemical reaction, the growth should involve a direct solid–solid phase transformation from Zn（OH）₂ to ZnO. Once branched structures of the flower-like ZnO nanostructure passed through the surface of dissolving Zn（OH）₂ crystal, crystal growth of ZnO nanostructure should obey a dissolution-reprecipitation mechanism. It was found that the flower-like ZnO nanostructure exhibitted a higher photocatalytic activity for methylene blue（MB）. After 120 min, its photocatalytic degradation rate could reach 94%.Again, nanostructures ZnO samples of different morphologies were synthesized with simple hydrothermal routes, using zinc acetate and sodium hydroxide as raw materials by changing the reaction parameters. It is shown that the different parameters such as concentration of OH-、mineralizer、zinc salt and surface active agent had an important influence to the morphologies and structures of the products. The ZnO nano powder with different morphology and structure was obtained with different OHconcentration; when the concentration was 0.16 mol/L, the product was formed with nano-columnar structure; while the product with the other three concentration was presented for the aggregation of nano-particle or nano-sheet. There was a big difference at the morphology and structure of the product with using different mineralizer. The product was formed with flower-like microstructure of nano-sheet with using KOH as mineralizer. However, the morphology of product with different zinc salt are similar, almost all of the aggregation of nano-sheet.The PL intensity of the product at different conditions are different, and its intensity are affected by structure and specific surface area of nanostructure. Under UV light irradiation, ZnO nanostructure had good performance of photocatalytic degradation of MO, the specific surface area of nanostructure was greater, the photocatalytic performance was better.