Fabrication Of ZnO And ZnO/NiO Nanofibers Via Electrospinning And The Study Of Their Photocatalytic Properties

Nanostructured semiconducting metal oxides are being widely utilized in the fields of solar energy conversion, sensors, catalysis and various electronic nanodevice due to their unique optical and electronic properties. Researches on nanoscale one-dimensional materials have become a significant part of nanotechnology and nanoscience. In recent years, many efforts have been made to fabricate various semiconductors nanofibers, which include the chemical oxidative polymerization method, the template method, in situ deposition polymerization, hydrothermal synthesis, and so on. Among these synthesis approaches, electrospinning technique due to its advantage of simple and efficient composition control has been exploited to manufacture nanofibers of polymers ranging from tens of nanometers to several micrometers and related materials into one-dimensional structural nanofibers with controllable diameters, compositions and porosities. As a result, in this thesis, we put forward an electrospinning combined with sol-gel, physical adsorption, respectively, to further explore the preparation of one-dimensional micro-nanostructured semiconducting metal oxides and the study of their photocatalytic properties.First, polyvinylpyrrolidone(PVP) is used as template. Hexagonal wurtzite ZnO nanofibers with special dendritic structure is successfully synthesized through electrospinning combined with sol-gel method and subsequent calcination techniques. According to statistic, the diameter of ZnO dendrite branch is about 100 to 200 nm. The photoluminescence spectra has confirmed that the ZnO nanofibers exhibited a broad visible emission mainly concentrate on the blue and blue-green emission bands. Furthermore, it also indicates the existence of surface oxygen vacancies in the Zn O crystallines, which probably relates with photocatalytic activity. Meanwhile, methyl blue is used to evaluate the photocatalytic activity of the ZnO nanofibers. By quantifying the degradation of methyl blue dye, the photocatalytic performance of the ZnO nanofibers annealed at 400 and 650℃ is investigated. The results manifest that the particular ZnO-650 with dendritic structure exhibits superior photocatalytic activity.Secondly, taking polyethersulfone(PES) as the main line, we prepare pure PES nanofibers by using electrospinning technology. In order to minimize the number of experiments, an orthogonal experiment is designed. It is not only helpful to optimize the spinning parameters for electrospinning PES fibers, but also conducive to measuring the influence of these parameters. The results exhibit that when the PES concentration is 34 wt.%, the applied high voltage is held at 13 kV, the collect distance is 26 cm and the feeding rate of the solution is controlled at 0.04 mm min-1 by means of a single syringe pump, the PES fibers with smoothest morphology and uniform diameter can be obtained. At the same time, the experimental results also indicate the polymer concentration has a greater influence on the fibers morphology.Finally, polyethersulfone(PES) can be considered as a new template for preparing inorganic composite nanofibers with special hollow structure since it has a good performance with thermal stability, hydrolysis resistance and chemical resistance. We use PES nanofibers as a template, combining electrospinning with physical adsorption and calcination technology to fabricate ZnO/NiO heterojunction nanofibers with hollow structure. After statistics, the ZnO/NiO hollow nanofibers show diameters of approximate 414 nm with the inner diameters of about 261 nm. The formation mechanism of the hollow ZnO/NiO heterojunction nanofibers is studied in detail by TGA and DSC. It is found that the formation of morphology is mainly ascribed to the high decomposition temperature of PES polymer. This illustrates that the morphology of semiconductor composite nanofibers is closely related to the thermal properties of polymers. Moreover, the photocatalytic performance test indicates that the ZnO/NiO hollow nanofibers exhibit higher photocatalytic activity than the pure ZnO and pure NiO nanofibers for the degradation of MO dye under UV light irradiation, which may be ascribed to the unique hollow structure and the highly efficient separation of photogenerated electron-hole pairs. Meanwhile, the photocatalytic mechanism of the hollow Zn O/NiO nanofibers is expounded.