Preparation Of Nano-Bi And Nano-Bi₂O₃ And Their Size-dependences Of Phase Transitions And Electrochemical

Bismuth nanoparticles and their oxides have been widely used in many fields,which often involve the problems about phase transition and electrochemistry of nanoparticles.As the nano effect,the phase transition and electrochemical properties of nanomaterials are significantly different from the corresponding bulk materials.However,the influence of particle size on the phase transition and electrochemical properties of nano-Bi₂O₃ and nano-Bi₂O₃has not been reported.Therefore,it study the phase transition and electrochemical properties of nano-Bi₂O₃ and nano-Bi₂O₃ in theory and experiment to clarify the influence regularities and influence mechanisms of size on the phase transition and electrochemical properties in this paper.At first,on the basis of the generalized thermodynamic equation of phase transition of nanoparticles,the relations of the thermodynamic properties of structural phase transition and the particle size was derived by using the core-shell model of nano-particle phase transformation.Then based on the theory of nano-systems reaction thermodynamics and the second law of thermodynamics,the relations of the electrode potential of nano electrodes,the thermodynamic properties of electrode reaction and the thermodynamic functions of nanoparticle interfaces,respectively,and the nanoparticle size were derived.More,the influences of particle size on the phase transition and electrochemical properties were discussed theoretically.Secondly,spherical nano-Bi with different particle sizes and Bi nanowires were prepared by microwave heating and hydrothermal method,and spherical nano-Bi₂O₃ and Bi₂O₃ nanoplates were prepared by hydrothermal method.The phase,composition,particle size and morphology of nano-Bi and nano-Bi₂O₃were characterized by powder XRD and FESEM.Differential scanning calorimetry?DSC?was used to determine the thermal curves of of nano-Bi and nano-Bi₂O₃ with different particle sizes,and then the phase transition temperatures and thermodynamic functions of nano-Bi and nano-Bi₂O₃ with different particle sizes were obtained.The influences of particle size on the thermodynamic properties of phase transition?phase transition temperature,phase transition enthalpy and phase transition entropy?were discussed and compared with the theoretical formula.Finally,nano-Bi electrode and nano-Bi₂O₃ electrode were prepared respectively.And the electrode potentials of nano-Bi electrode and nano-Bi₂O₃electrode with different particle sizes were measured by potentiometer at different temperatures.Then the corresponding thermodynamic quantities of the electrode reactions?electrode potential,temperature coefficient,reaction Gibbs free energy,reaction enthalpy,reaction entropy and equilibrium constant?were obtained respectively.And the surface thermodynamic functions of nanoparticles?molar surface Gibbs energy,molar surface enthalpy and molar surface entropy?were also obtained,the influences of particle size on the thermodynamic quantities and the surface thermodynamic functions of nanoparticles were discussed and compared with the theoretical formula.The results indicate that,?1?Spherical nano-Bi with different particle sizes can be prepared by hydrothermal method.The type of dispersants and the amount of sodium polystyrene sulfonate?PSS?have great influence on the morphology of nano-Bi,and with the increase of reaction time,the particle size of the prepared nano-Bi increased.Spherical nano-Bi₂O₃ with different particle sizes can be prepared by solvothermal method.The concentration of nitric acid,the type and amount of dispersant and reaction time have significant effect on the particle size of nano-Bi₂O₃.The particle size of nano-Bi₂O₃ firstly increases and then decreases with the increase of nitric acid concentration,and the type of dispersant has a great influence on the morphology and particle size of nano-Bi₂O₃,and the particle size of nano-Bi₂O₃ decreases with the increase of the content of polyvinylpyrrolidone?PVP?.With the increase of reaction time,the particle size of nano-Bi₂O₃ increases.?2?The particle size has a significant effect on the thermodynamic properties of phase transition of nano-Bi and nano-Bi₂O₃,and the effect of particle size on the thermodynamics of melting and structural transformation is the same:the temperature,the enthalpy,the entropy of phase transitions decrease with the decrease of particle size,and are linearly related to the reciprocal of particle size,respectively.These effects are consistent with the above theoretical relations.?3?The particle size has a significant effect on the electrode reaction thermodynamics and surface thermodynamics of nano-Bi and nano-Bi₂O₃:with the decrease of particle size,the standard electrode potential and the logarithm of equilibrium constant of nano-Bi electrode decrease,the temperature coefficient,Gibbs free energy,entropy and enthalpy of the electrode reaction increase.Effect of particle size on reaction thermodynamics of nano-Bi₂O₃electrode is contrary to that of nano-Bi electrode,it can be attributed to the nano-Bi₂O₃ as a reactant in the electrode reaction.With the decrease of particle size,the molar surface Gibbs energy,molar surface enthalpy and molar surface entropy increase.And these thermodynamic quantities are linearly related to the reciprocal of particle size,respectively.These effects are consistent with the above theoretical relations.This paper not only solves the size-dependence of the phase transition and electrochemical properties of nano-Bi and nano-Bi₂O₃,but also has important reference for the preparation,study and application of the phase change and electrochemical properties of other nanomaterials.