Design Synthesis And Photoelectrochemical Property Of One-dimensional Aligned Nanostructures

Recently, one-dimensional （1D） nanostructures have aroused intensive research interest due totheir potential application in nanodevices. Therefore, it has important theoretical and practicalsignificance to achieve design synthesis of1D nanomaterials with controlled nucleating sites,morphologies, arrangement, components, which is foundation and prerequisite for the applications of1D nanomaterials. In this dissertation, a series of significances have been obtained on the designsynthesis of1D nanomaterials and relative application, which can be summarized as following:（1） Based on the natural patterns of phase texture distribution of （α+β） biphase brass substrate,the patterned quasi-aligned Zn₂GeO₄-coated ZnO nanowires were synthesized by one-step thermalevaporation of the mixture powders of GeO2and C. It is observed that following the self-catalyzedeffect of the Zn clusters, aligned Zn₂GeO₄-coated ZnO nanowires grow site-selectively on thesurface of island-shaped α phase and form novel patterns which inherit the distribution of α phase onthe substrate. According to the pattern and feature of phase texture distribution of the alloy substrate,we can synthesize the patterned nanowires arrays with controlled location and distribution in a moreeffective way.（2） Bulk-quantity of chain-like GeO2/Zn₂GeO₄core/shell heterostructures have been achievedon the Cu-Zn（41wt%Zn） substrate by a thermal evaporation of Ge powder. The Cu-Zn alloysubstrate can also provide Zn vapor for the synthesis of Zinc compounds through dezincificationprocess. Nanochain networks with “X” and “Y” type junctions have been prepared and the growthmechanism for the chain-like GeO2/Zn₂GeO₄core/shell heterostructures is discussed.（3） A convenient method for the direct and large-area synthesis of1D ZnO nanostructures on aconductive brass substrate has been developed, consisting of thermal oxidation of a Cu59Zn41alloyfoil. Various1D nanostructures such as microsheets, nanocombs, nanobelts, and nanorods have beenin situ grown on the alloy substrates under different annealing temperatures. In this preparation, theCu59Zn41alloy foil functions as both substrate and Zn source for the growth of1D ZnOnanostructures.（4） In₂O₃nanorod arrays have been successfully synthesized on the Cu–Sn （5at%Sn） alloysubstrate by one-step thermal evaporation of the mixture powders of In₂O₃and C. The site-specificgrowth of In₂O₃nanorod arrays is realized by annealing Cu–Sn alloy lightly below the solidus line,where grain-boundary triple junctions can be wetted preferentially. As a result, the catalyzing alloydroplets will be present at the sites of grain-boundary triple junctions, which will control the growthof In₂O₃nanorods at defined locations by the vapor–liquid–solid growth mechanism. This growthtechnique provides a cost-effective and simple approach to fabricate ordered nanorod arrays with the sites controlled, which may benefit nanorod device applications.（5） The novel structured Ga-doped In₂O₃nanoleaves are synthesized by a simple one-stepcarbonthermal evaporation method using Cu–Sn alloy as the substrates. Two basic parts constructthis leaf-like nanostructure: a long central trunk and two tapered nanoribbons in symmetricdistribution in relation to the trunk. The Cu-Ga–In alloy particles are located at or close to the tips ofthe central trunks and serve as catalysts for the central trunk growth by the vapor–liquid–solidmechanism. And the homoepitaxial growth of tapered nanoribbon on the surface of the central trunkcan be explained by vapor–solid mechanism. The naturally good adhesion or electrical connectionbetween the nanoleaves and conductive substrate has been realized.（6） The flower-like ZnO nanorods clusters have been prepared via simple hydrothermal methodunder low temperature. The as-prepared products with different solution concentrations are used aslight anodes for dye-sensitized solar cells （DSSCs） to form a “sandwich” DSSCs devices. The resultsshow that as solution concentrations increased, the short-circuit current density （JSC） decreases,while, no significant change in open circuit voltage （VOC） and fill factor （FF）. For the flower-likeZnO nanorods, the JSCand overall power conversion efficiency （η） can reach a maximum of1.33mAcm^-2and0.3%, respectively.（7） The well-aligned ZnO nanowires have been successfully synthesized via a low-temperaturehydrothermal route on glass substrates pre-deposited with ZnO seeding layer. The results show thatthe increasing the solution concentration results in the formation of nanowires with lager diameters,while, has a less influence on the packing density of the products. The length and aspect ratio can beincreased by introducing the fresh solution bath. And the nanowires are found to be tightlyphysically and mechanically joined with the substrate pre-deposited with thick ZnO seeding layer.The as-prepared products with different solution concentrations are used as light anodes fordye-sensitized solar cells （DSSCs） to form a “sandwich” DSSCs devices. As solution concentrationsincreased, the short-circuit current density （JSC） decrease. For the ZnO nanowire arrays, the JSCand ηcan reach a maximum of3.44mAcm^-2and1.03%. The performances of the solar cells and itsadvantage base on the aligned nanowires as anode compared with flower-like ZnO nanorods arediscussed.（8） Using sodium tripolyphosphate （STTP） as the surfactant, the multistacked nanoplatescapped on the pre-synthesized ZnO naowire arrays are obtained. The results show that themultistacked nanoplates not only increase dye loading but also function as scattering particles toincrease light harvesting efficiency of the solar cell. The test of photoelectric conversioncharacteristics of the cell fabricated by ZnO nanowire/nanoplate composite film shows that its JSCis3.35mA/cm2, VOCis0.66V, FF is56%and η is1.24%. （9） Heterostructured ZnO/ZnS core/shell nanowire arrays are successfully fabricated to serve asphotoanode for the dye-sensitized solar cells （DSSCs） by a facile two-step approach，combininghydrothermal deposition and liquid-phase chemical conversion process. The results show that thecompact ZnS shell can effectively promote the photogenerated electrons transfer from the exciteddye molecules to the conduction band of the ZnO, simultaneously suppress the recombination for theinjected elelctrons from the dye and the redox electrolyte. As reaction time goes by, the surface ofthe nanowires becomes coarse due to the new formed ZnS nanoparticles, which will enhance the dyeloading, resulting in increment of the JSC. For the ZnO/ZnS core/shell nanostructures, the JSCand ηcan reach a maximum of8.38mA/cm2and1.92%after6h conversion time, corresponding to12-fold and16-fold increment of as-synthesized ZnO, respectively.