Researches Into Preparation Of Nano-copper With Different Shapes And Sizes And Its Melting And Electrochemical Properties

The melting and electrochemical properties of nanomaterials significantly differ from those of the corresponding bulk materials,which depends on the particle size and shape of the nanoparticles.However,the studies on the effects of particle size and shape on the melting thermodynamics of nanoparticles remain imperfect,and the effect of shape on the electrochemical properties of nanoparticle electrodes is still unclear.The melting and electrochemical properties are often involved in the researches,preparations and applications of nanomaterials,it is therefore worthy to give intensive investigations on the melting and electrochemistry of nanoparticles in theory and experiment to clarify the influence regularities and influence mechanisms of size and shape on the melting and electrochemical properties in this paper.In terms of the melting thermodynamics,the thermodynamic relations between melting temperature and particle size of nanoparticles with four shapes were deduced,and the influence regularities of shape and size on the melting temperature of nanoparticles were discussed.Then the melting and electrochemical properties of nano-copper particles were selected as the research system,and the spherical nano-copper,the octagonal prism nano-copper,the copper nanowires and copper nanocubes were prepared by the methods of microwave irradiation,hydrothermal process,and liquid reduction,respectively.The size and morphology of the samples were characterized by X-ray diffraction?XRD?and scanning electron microscopy?SEM?.The melting curves of nano-copper with different shapes and size were measured by differential scanning calorimetry?DSC?,and the initial melting temperature?To?,the melting temperature at the maximum rate?TM?,the melting enthalpy??slHm?and the melting entropy??slSm?were obtained.The influence regularities of size on the melting thermodynamic properties were compared with the corresponding theoretical relations.In terms of the electrochemistry,by introducing a shape parameter,relations between the electrode potential,the temperature coefficient and the electrode reaction thermodynamic functions,respectively,and size of nano-copper electrode were first deduced,and the influence regularities of the shape and size on the electrode reaction thermodynamics of nanoparticles were discussed.By measuring the electrode potentials of nano-copper electrodes at different temperatures,the standard electrode potential?Eo?,the temperature coefficient?????p,equilibrium constant?lnko?,the molar reaction Gibbs energy??rGmo?,molar reaction entropy??rSmo?,molar reaction enthalpy??rHmo?,as well as the reversible reaction heat?Qr?of nano-copper electrode were obtained,and the influence regularities of shape and size on the electrode reaction thermodynamic properties of nano-copper were compared with the corresponding theoretical relations.The mechanism of electrode process and the influence regularities of shape and size on the electrode reaction kinetics of nano-copper electrode were discussed according to the results of cyclic voltammetry curves.The results indicate that:?1?The particle size of spherical nano-copper is influenced by the concentration of CuCl₂ solution,the pre-set temperature,the raw material ratio and the reaction time.The pre-set temperature is the main influence factor.The amount of octadecylamine?ODA?,the reaction temperature and the reaction time significantly affect the shape and size of octagonal prism nano-copper.Copper nanowire and nanocube can be prepared by adjusting the amount of hexamine?HDA?.?2?Both the shape and size have significant effects on the melting thermodynamic properties of nano-copper.With the decrease of particle size,the melting temperature,enthalpy and entropy decrease and linearly vary with the reciprocal of particle size.The effect of shape on the melting thermodynamics of nano-copper is as follows:at the same equivalent diameter,the melting thermodynamic functions of spherical nano-copper are bigger than those of the octagonal prism and the copper nanocube.The influence regularities are consistent with the related theory.?3?Both the shape and size have significant effects on the electrode reaction thermodynamics of nano-copper.With the particle size decreases,Eo and In Kodecrease,while?????p??rGmo??rSmo and ?rHmo increase.In addition,the E°?lnko??????p??rCmo??rSmo and ?rHmo are linearly related to the reciprocal of nanoparticle size.The effect of shape on the electrochemical thermodynamics of nano-copper are as follows:in identical equivalent diameter,Eo?sphere?>Eo?nanowire?>Eo?octagonal prism?;the electrode reaction thermodynamic functions of copper nanowire are the smallest,those of the spherical nanoparticles are the next,and those of the octagonal prism and the copper nanocube are bigger.The influence regularities are consistent with the related theory.?4?Both the shape and size have significant effects on the electrode reaction dynamics of nano-copper.With the decrease of particle size,the peak voltage presents a left shift and the peak voltage of the electrode process linearly vary with the reciprocal of particle size.The peak current value increases with the decrease of particle size,and the peak current value of the electrode process is linearly related to the reciprocal of particle size.The electrode reaction is a quasi-reversible system,and the reversibility of the electrode reaction deteriorates with the decrease of particle size.The effects of shape on the electrode reaction thermodynamics of nano-Cu are as follows:in the range of the measured equivalent particle size,the reversibility of spherical nano-copper electrode is the best,followed by the copper nanowire electrode,and the octagonal prism and copper nanocube electrode in sequence.