The Controlled Synthesis Of Pd Nanocrystals And Their Epitaxial Growth And Performance Research

Due to its excellent catalytic, optical and electrical properties noblemetal nanocrystals have potential applications in many fields. Theperformance of noble metal nanocrystals have a close relationship with itssize, morphology and structure, so its controllable synthesis is of vitalimportance and become a hotspot project recently. In this dissertation,based on hydrothermal synthesis method and epitaxial growth,monodispersed Pd and Pd-Au, Pd-Ag heterostructure were synthesized.Furthermore, it explored the growth mechanism and studied therelationship between catalytic properties and structure of nanocrystals.The main research work is listed as following:(1) Compared with Au and Ag, Pd is more susceptible to the externalfactors such as O2and halide ions. For this reason, controlled synthesis ofPd nanocrystals is more difficult, expecially controlled synthesis of thetwin structure has been a huge challenge. A strategy that employs smallorganic molecules (acetonitrile, acetone,1,4-dioxane, and1,3,5-trioxane;ethanol and isopropanol) for selective synthesis of five-fold twinnednanowires and single twinned right bipyramids of Pd was developed. Theyield and purity of them were well improved. The interaction betweensmall organic molecules and halide ions have different ability to decreasethe oxidative etching of O2/halide pair. After that, the control of twinnednanostructures of Pd is allowed. And on this basis, we examined itsforming mechanism in detail. Own to Pd nanowires have more twinboundaries, more defects and disordered atoms would appear in Pdnanowires. Therefore, Pd nanowires are more active than bipyramids forcatalyzing the reduction of4-nitrophenol. The results in this work providea new idea to tune etching degree of O2/halides for controlling twinnedstructure of noble metals in a hydrophilic system. In addition, this paper also confirms that twinned structures is conducive to obtain highercatalytic activity.(2) By using Pd five-fold twinned nanowires or Pd single twinnedright bipyramids as seed and modifying the factors which could be havingan influence on reaction kinetics, such as reactant concentration, reducingpower of reductant and pH, Au can selective epitaxial growth on the Pdnanocrystals. Au-Pd heterostructure nanocrystals with various shapesare obtained by this mean. Besides that, this paper also explored therelationship between the reaction activity of catalyzing the reduction of4-nitrophenol and the composition and microstructure of Au-Pdheterostructure.(3) The paper controlled synthesis of Ag-Pd heterostructurenanocrystals by using the Pd five-fold twinned nanowires as seed andcontrolling reaction kinetics factors, such as reactant concentration,reducing power of reductant and pH. The Ag-Pd heterostructurenanocrystals have different coverage degree. And on this basis, westudied its growth processing in detail.