| Summary: | 博士 === 國立清華大學 === 化學系 === 96 === We present the syntheses of ZnO, Au2S and CuS nano/microstructures by using a hydrothermal method. ZnO microstructures were formed by using zinc nitrate hexahydrate (Zn(NO3)2•6H2O), hexamethylenetetramine (HMT, or C6H12N4), and trisodium citrate (TSC) reagents. ZnO microspheres were prepared after 1 h of reaction and are amorphous. By increasing the reaction time, these microspheres gradually dissolved to form short hexagonal microrods with stacked nanoplate or nanosheet structure. The microspheres exhibit an extensive growth of interconnected sheetlike nanostructures and possess high surface areas. These ZnO microspheres can be used in the photodecomposition of phenol under direct sunlight irradiation after heat treatment to 300 °C. Trisodium citrate plays a key role in directing the formation of these microstructures because the ZnO microrods were formed under the influence of trisodium citrate.
Uniform size of 2–4 nm Au2S nanoparticles were formed by using tetrachloroauric acid (HAuCl4) and sodium sulfide (Na2S•9H2O) reagents and CTAB surfactant. These Au2S nanoparticles were found to assemble into a densely packed lamellar phase structure, and the resulting materials display an overall cross-sheet-like morphology. The sheets are 125–250 nm in length and can be suspended in solution. Although some isolated faceted gold nanoparticles were also observed, XRD, TEM, XPS, and EDS characterization of the nanoparticle samples confirmed the composition of the nanoparticles as Au2S. UV–vis absorption spectra also showed only absorption feature from the Au2S nanoparticles. Sufficiently high concentrations of Na2S and CTAB in the reaction mixture were concluded to be necessary to promoting the growth of Au2S nanoparticles, and reducing the production of gold nanocrystals. The growth mechanism of Au2S nanoparticle superstructures is related to the decomposition of CTAB. The thermolysis of CTAB was studied and the results indicate that long alkyl chains interact with the Au2S nanoparticles and direct their assembly into a lamellar phase structure.
The synthesis of hexagonal covellite (CuS) nano/microdisks can be achieved by using a hydrothermal method at 90 to 220 °C. A glass tube with a capacity of 6 mL was used as the reactant container and was sealed by torch. Copper chloride (CuCl2) and Na2S were used as reagents, CTAB was selected as surfactant and sulfuric acid (H2SO4) was chosen as the acid source to maintain an acidic environment during the hydrothermal process. The need of H2SO4 to form CuS crystals is discussed. CuS nanodisks were collected under the reaction temperatures of 90 to 150 °C. The particle size of CuS nanodisks can be controlled by using different reaction temperatures but are usually associated with a large size distribution. CuS nanodisks show two absorption features in the UV�{vis and infrared region. CuS microstructures containing hexagonal disks and crisscross disks can be obtained after hydrothermal synthesis at 220 °C. Besides, CuInS2 nanocrystals can be synthesized by using a similar reaction condition.
We have used a vapor phase transport method for the growth of ultralong ��-Ga2O3 nanowires and nanobelts on silicon substrates. The growth was carried out in a tube furnace with gallium metal serving as the gallium source and Au-coated Si wafer as the substrate. The nanowires and nanobelts can grow to lengths of hundreds of micrometers and even millimeters, and they display strong blue emission by irradiation with an ultraviolet (UV) lamp. The blue emission shows a band maximum at 470 nm. Their full lengths and strong blue emission have been captured by optical images. Interestingly, horizontal Ga2O3 nanowire growth on the silicon substrates can be observed by annealing the silicon substrates in an oxygen atmosphere to form a thick SiO2 film, and growing Ga2O3 nanowires over the sputtered-gold patterned regions. Their composition has been confirmed by TEM characterization. This represents one of the first examples of direct horizontal growth of oxide nanowires on substrate.
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