| Nanometer materials refer to the nano-level size (1-100nm) of at least one dimension in three dimensional space or materials consisting of or using them as a basic subject. Because of its different performances distinct from macro materials, nano materials cause great attention in the scientific community and business area. Recently, template preparation of nano materials has attracted a great deal of attention. This method can make the controlling of the size, morphology and structure of the nano materials come true, based on the space confined effect of the template. Porous Anodic alumina membrane (Anodic aluminum oxide, AAO) as a kind of very good template material, is widely used in the synthesis of nanostructures, especially the preparation of orderly array and one-dimensional nano materials. Its aperture is in 5～500 nm range, the porosity is as high as 1011-13/cm2, and the channel length can reach several to hundreds of micrometers. It has excellent properties, such as, simple and economic preparation technology, uniform aperture size, good controllability and of nanometer materials with similar structure characteristics to the template hole. At present, AAO template has been succeeded in the preparation of conductive polymers, metals, semiconductors and carbon nano fibers and nanotubes, adopting by electrochemical deposition, chemical deposition (also known as chemical bath), chemical polymerization, sol-gel method and chemical vapor deposition method.Cadmium sulfide (CdS) belongs to Ⅱ-Ⅵ semiconductor material, and is a direct bandgap semiconductor like other semiconductor materials in the family. Its forbidden band width is 2.42 eV at room temperature, belonging to the category of visible light. Nanoscale CdS has special performance differing from the massive material for quantum size effect, small size effect, surface effect and macroscopic quantum tunnel effect. For example, its first level excited state will increase with the decrease of the particle size, and the energy gap will widen, which leads the light absorption band widespread to the short-wave direction and bring out "blue shift" phenomenon. Therefore, CdS is widely used in optoelectronic field, such as semiconductor devices, nonlinear optics, light emitting diode, light active waveguide, electroluminescent materials, communications, information storage, high integration of chemical or biological sensors, catalysis, solar panels and fluorescent tags, and so on. This paper parpared Anodic aluminum oxide (AAO) membranes with one-time Anodic oxidation method and twice Anodic oxidation, and obtained cadmium sulfide (CdS) nanowires of hexagonal system structure, by chemical bath deposition method and using the AAO gained from twice Anodic oxidation method as template. The main research contents and conclusions are as follows:1. After comparing the two methods, AAO membranes were prepared mainly by anodic alumina membranes prepared by two-step oxidation, the influence of different oxidation reaction time on the preparation of anodic alumina was studied, and best condition of preparation process was explored. The phase and the surface morphology as well as size of the AAO membrane were detected and analyzed by X-ray powder diffraction (XRD) and scanning electron microscope (SEM). The XRD analysis results show that the AAO membrane is made up of amorphous alumina, no existing of aluminium base not oxided entirely, which shows that the quality of the preparaed AAO membrane is high. The SEM results show that the AAO membrane has orderly holes, basically consistent aperture size, and consistent hole shape (approximately assumes circular); each unit of the membrane tends to hexagon, and the aperture size is about 90 nm. It illustrates that the obtained AAO template conforms to the requirements of the experiments, and can be used for the preparation of cadmium sulfide nano materials. The best preparation condition is gained by comparing the SEM figures of AAO membranes prepared under different oxidation reaction time, that is the most proper time for the first anodic oxidation is 12 h.2. The reaming of the holes of the AAO membrane prepared by twice anodic oxidation was studied, with 5%phosphoric acid solution and under 25℃. It shows that only the aperture changes along with the increase of expanding time, while the whole morphology of AAO membrane keeps good, through Comparing the SEM figures after reaming of AAO membrane with before the reaming. After calculating, we know that the expanding rate of AAO membrane hole on the diameter direction is about 1 nm/min, and the increase of the diameter with the corrosion time assumes linear relationship approximately. The variation curve shows that the hole diameter increased with the increase of corrosion time. It is implied that the AAO template aperture size can be controlled by by adjusting the corrosion time to choose AAO membrane with certain aperture size needed for the experiments. Besides, it can be seen from its fluorspar spectrogram that the AAO membrane has strong fluorescence property, and the strong fluorescence emission peak is mainly at 425 nm. This may be due to the flaw of the AAO template hole itself.3. Using cadmium chloride [CdCl2·2.5H2O] and thiourea [H2NCSHN2 or (NH2)2CS] as cadmium and sulfur sources. CdS nanoparticles and nanowires were respectively prepared by hydrothermal method and AAO template method. The XRD analysis shows that the CdS nanoparticles obtained from hydrothermal method are mainly of hexagonal system; SEM results show that the sample contains large ball particles at size of a few microns, which consist of a large number of irregular shape "gravel" small particles (about 100 nm in diameter) and exist a phenomenon of reunion. It is discovered that the CdS nanowires prepared by chemical bath method and with homemade AAO membrane for the template are also of hexagonal system structure, through the analysis of the XRD and standard JCPDS card. The XRD figure does not appear other impurity peak, which means that elemental Cd and S does not exist in the sample. The morphology characteristics of the CdS nanowires were detected and analyzed by transmission electron microscope (TEM) and digital micrograph software. It is found that the CdS nanowires were uniform, orderly and neat, joint length is 5.5μm and the diameter is about 90nm. Through the analysis of fluorescence spectrum, we know that the CdS nanoparticles prepared by hydrothermal method have two strong fluorescence emission peaks at 415nm and 583nm, while the CdS nanowires mainly appears emission peak at 445nm, occurring "red shift" and "blue shift" phenomenon respectively compared with the former two emission peaks.This paper finally has carried on the full text summary and outlook for future work. It can try to use direct current (dc) and alternating current (ac) on the AAO template preparation of CdS nanowires, respectively, and compare the differences of morphology and properties with the CdS nanowires prepared by chemical bath method. In addition, it can try to embedd CdS and Fe3O4 on the AAO template, so to prepare composite materials with both properties of fluorescence and magnetic. It can also continue to doping rare earths in the composite materials and study their physical and chemical properties. |
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