Precise Synthesis,Controllable Assembly of Functional Nanowires and Structure-Property Relationship of Nanowire Assemblies

Author:Chen Qing Xia

Supervisor:yu shu hong


Degree Year:2019





One-dimensional(1D)nanostructures considered as an ideal quantum particles transport carrier have received more and more attention in recent years,due to their radius generally down to some characteristic sizes(e.g.Bohr radius,wavelength of light,phonon mean free path,magnetic domain critical dimension and exciton diffusion length).Since Yang made a review on semiconductor nanowires in 2010,the research of nanowires has become one of the hot spots in the field of nanotechnology.The application field also gradually extends to electronics,energy storage,optoelectronic devices,sensors and catalysis,biology,etc.,and even shows a promising potential in emerging artificial skin,nano electronic devices,photovoltaic cells and biological electronics.Therefore,the precise and effective synthesis of uniform nanowires with controllable morphology and composition is still an extremely important scientific issue.And the diversity of nano wire materials plays a fundamental and irreplaceable role in discovering new phenomena and exploring new properties.The most serious obstacle to the practical application of nanomaterials lies in the intrinsic properties of nanostructured assembly blocks.How to process nanostructured assembly blocks into macroscopical bulks with specific functionalities will be a long-tcrm research ehallenge.At present,many remarkable breakthroughs in nano-assembly have been achieved,such as the creative design of exquisite three-dimensional(3D)network structure and the great advantages of maeroseopic assembly in fire and heat insulation.Assembly methods,assembly block attributions and assembly structures will have decisive effects on the output performance of the assembly bulk.Therefore,it is necessary to study the structure-function relationship between assembly block,assembly bulk and assembly performance.Therefore,this diss ertation involves the precise synthesis of ID axial segmented heteronanostructures,the precise control on ID ultrathin nanostructure components,and the design of ID nanostructured assembly structures and performance research,by means of the ultrathin Te NWs and gas-liquid interface assembly technology.The main research results are as follows:1.A general wet-synthesis based on under-stoichiometric reaction for ID axial segmented heteronanostructures is proposed,and mechanical simulations based on the phase-field model is employed to probe into the underlying evolution mechanism.By adding metal precursors with under-stoichiometric ratio to Te NWs,heterogeneous nanowires with the alternating axial distribution of tellurium and telluride can be obtained.Mechanical simulations suggest the three-stage evolution process,i.e.,island generation,stripe penetration and segment ordering.Mechanical calculations also demonstrate near attracts-far repels determined by elastic energy minimization,rendering the interface movement and segment ordering in disordered stripes.With subsequent chemical transformations,we realize a library of lD-SHs,including 25 NW-NW and NW-NT nanostructures with 13 elements involved.This provides a broad tool set for the synthesis of well-designed axially segmented heteronanostructures and offers new perspectives for understanding the formation of periodic nanostructures.2.We demonstrate an approach to synthesize a class of ID multicomponent Pt-based NWs and NTs and investigate their composition-dependent performances for MOR.Among the as-obtained catalysts(i.e.,PtTe NWs,PtAgTe NWs,and PtRuAgTe NTs),PtRuAgTe NTs deliver the best MOR performance due to the tube-like structure and rough surface,as well as the synergistic effect between compositions.The introduction of Ag、Ru results the downshifting of d-band center position of Pt and thus much easier desorption of intermediates.In addition,synchrotron radiation photoelectron spectroscopy shows that PtRuAgTe NTs exhibit structural evolution during MOR,generating Pt ’skin’ structure.The present work may open up opportunities to couple the reasonable composition and structure design of ID Pt-based catalysts with extremely high activity and superior durability for fuel cell reactions.3.A well-designed ’regulation of the surface reactant flux(RSF)’ strategy based on strongly directional micro-electric field(MEF)distribution is demonstrated for electrocatalytic performance improvements.The boosted electrocatalytic performance is achieved by aligning catalyst to construct strongly directional MEF thus rendering optimal extra reactant flux to the catalyst with MOR and Pt NTs as model reaction and model catalyst,respectively.A reaction-diffusion kinetic model based on the free energy density functional was established to simulate the approaching of reagent molecules to the catalyst.Simulation results unveil that RSF derives from the gradient of the MEF formed on ordered catalyst pattern,which gathers reagent molecules much more efficiently,thus vastly optimizes the kinetic process and electrocatalytic performance.This ’RSF’strategy can be readily extended to other catalytic system or using other nanosized building blocks with different components and dimensionalities to enhance electrocatalytic performance.We believe this novel work would open a new avenue in energy conversion field,offering an ingenious structural motif to optimize electrocatalytic performance.