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Electrochemically Shape-Controlled Synthesis of Fe Nanoparticles, Their Structural Characterization and Properties

Author: ChenYanZuo
Tutor: SunShiGang
School: Xiamen University
Course: Physical and chemical
Keywords: Shape-controlled Synthesis Iron THE SINGLE Open structure crystal surface Electrocatalysis
CLC: TB383.1
Type: Master's thesis
Year: 2009
Downloads: 192
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Abstract

In general, the catalytic activity of metal nano to increase in the following two ways: First, changing the metal nano catalyst composition, that is, by changing the chemical composition and electronic structure. Second, changing the atomic arrangement of the surface of the catalyst metal nanoparticles, i.e., by tuning the surface geometry, the latter can be controlled by morphology synthesis. This is also an important technology of nanotechnology frontier research fields. Electrocatalytic and heterogeneous catalytic reactions are surface reactions, the catalyst effect of the key is the interaction between the surface atoms with reactive molecules. Therefore, if controlling the synthesis by morphology, prepared by having a surface atomic arrangement of the open structure of the metal catalyst, can significantly improve the activity and selectivity of the catalyst. The preparation of the catalyst of this will have important and far-reaching impact. Electrochemical method has unique advantages, was proved to be a nano particle shape control synthesis of important, this method is usually on a conductive substrate, metal electrode through the cathodic reduction the prepared metal nano-particles or thin films, the resultant load can directly for eletrocatalysis. The biggest advantage is that the method into nuclear bit by changing the deposition conditions, it can (nucleation time, growth potential, growth potential, and the bath concentration), to achieve the purpose of the precise adjustment of a nanocrystal growth velocity of each crystal face, and thus obtained by the specific crystal surface composition of nanomaterials. Addition, electrodeposition, the metal nanoparticles are fixed on the electrode surface, significantly eliminate the reunion phenomenon can not be stabilized in the plating bath, which is conducive to the catalytic performance. In this paper, we develop a control and the growth of the crystal surface structure of metal nano-programmed potential step electrodeposition method to achieve a precise control of the shape and surface structure of Fe nanocrystals. Achieved major results are as follows: 1. Using cyclic voltammetry (CV) and potentiostatic electrodeposition method (CA), glassy carbon (GC) substrate prepared with cube structure of Fe single crystal nanoparticles by SEM, HRTEM XPS, XRD, and other means of its composition, morphology and structure. successfully passed the test conditions change, change the size of the particle size of the cube-shaped Fe single crystal nano control, a series of particle size distribution of the cube-shaped single crystal Fe nanoparticles. The cube-shaped Fe single crystal nano particle growth mechanism and electrocatalytic activity and meticulous research. On the the body Fe electrodes and nano Fe electrode activated surface area of ??the calibration method. Development program potential step electrodeposition method using a step potential method to glassy carbon (GC) for the base, through the precise control of the growth potential of the system to change the surface of the nanoparticles various (hkl) Miller indices of two-dimensional nucleation growth rate, achieve precisely regulated Fe nanocrystal shape and surface structure. Successfully prepared the dodecahedron tetragonal bipyramid series eighteen icosahedral, as well as cube Fe single crystal has a perfect crystal form diamond nanoparticles. Single crystal Fe nanoparticles of different morphologies prepared catalytic properties of catalytic nanoparticles of Fe single crystal R is proportional to the degree of openness of the performance to its surface. Measured in 0.2MNaOH 0.01MNaNO _{the 2} solution,-1.188V at constant the potential reaction 200s, the the cube shaped Fe nanocatalysts generated steady-state reduction current density j _cube -7.126 mA.cm ^{-2 , the the 18 icosahedral catalyst generated approximately the same experimental conditions steady reduction current density of 1.8 to 4.8 times (j _{18-facet polyhedra -3.985 ~ 1.486 mA.cm ^{-2 ); approximately rhombic the the dodecahedron / tetragonal bipyramid 27 times (j _RD ≈ j _{RD < / sub> about -0.26 mA · cm ^{-2 ); approximately 18 times the body Fe catalyst (j _bulk-Fe = -0.39 mA · cm ^{-2 ). 6. Programmed potential step electrodeposition method, glassy carbon (GC) for the base, through regulation into nuclear power bit and nucleation time, successfully prepared octupole, dendrites and parallel to the crystal form of single crystal Fe nano particles. Octupole surface structure observed by SEM, STM technology and characterization, analysis and propose possible growth mode. In addition, through the use of SEM technology systems and detailed study of the growth of dendrites and parallel with crystal form single crystal Fe nanoparticles and to use HRTEM and SAED analysis of the structure of the crystal surface. The results showed that the nitrite electrocatalytic reduction process, the octupole and dendritic Fe nano-catalysts exhibit catalytic activity than the cubes Fe higher. This thesis is the development of metal nano catalyst surface structure control and growth program potential step electrodeposition method, not only the preparation of a series of different morphologies of Fe single crystal nanoparticles verify its findings from experiments on two-dimensional nucleation growth theory. The study results also showed that the electrochemical method is a very effective method, in nanocatalysts shape control and synthesized the journey,. It provides an effective way for the synthesis and preparation of more and more efficient catalyst.}}}}}}

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