The Effects Of Particle Size And Morphology On Electrochemical Thermodynamic Properties And Photocatalytic Performance Of Nano-SnO₂

Nanomaterials exhibit different peculiar properties from the corresponding bulk materials due to the nano-effects.As an important semiconductor material,nano-SnO₂ has been widely applied to electrode materials,photocatalysts,gas sensors and other fields.However,the mechanisms and regularities of the influencing of particle size and morphology on the electrochemical thermodynamic properties and the surface thermodynamic properties of nano-SnO₂ have not been reported so far,and the influence of particle size on the photocatalytic performance of nano-SnO₂ hollow spheres has not been clear.In this paper,the effects of particle size and morphology on the electrochemical thermodynamic properties of nano-electrode were studied theoretically.Based on the reaction thermodynamics of nano-systems,by introducing the equivalent diameter and morphology factor,the generalized relations between the electrode potential,temperature coefficient of electrode potential,reaction equilibrium constant,reaction Gibbs energy,reaction entropy,reaction enthalpy,reversible reaction heat composed of several dispersed phases with different particle sizes and morphologies,respectively,and particle size and morphology of each dispersed phase were derived.The influence mechanisms and regularities of particle size and morphology of the dispersed phase on the electrochemical thermodynamic properties of nano-electrode were discussed.Then,in experiments,using the electrode reaction and photocatalysis of nano-SnO₂ as the research system,the effects of particle size and morphology on the electrochemical thermodynamic properties and photocatalytic performance of nano-SnO₂ were studied.Firstly,nano-SnO₂ solid and hollow spheres and nanorods with different particle sizes were prepared by hydrothermal and solvothermal methods,and the influencing mechanisms and regularities of different preparation conditions on the particle size and morphology of nano-SnO₂ were investigated.Then,the potential of nano-SnO₂ electrode with different particle sizes and morphologies at different temperatures was measured by potentiometer,and the temperature coefficient of the electrode potential,reaction equilibrium constant,reaction thermodynamic properties,reversible reaction heat and surface thermodynamic properties were obtained.The influence regularities of particle size and morphology on the reaction thermodynamics of nano-SnO₂ electrode was obtained and compared with the corresponding theoretical relations.Finally,the effects of particle size and morphology on the photocatalytic degradation of salt-based magenta by nano-SnO₂ were investigated by using the prepared solid spheres,hollow spheres and nanorods.The results show that:(1)In terms of preparation of nano-SnO₂:nano-SnO₂ solid spheres with uniform particle size distribution and good dispersion can be prepared by hydrothermal method.The reaction temperature,reaction time and the dosage of surfactant are the main factors of influencing the particle size of nano-SnO₂solid spheres.With the increase of reaction temperature and reaction time,the particle size of solid spheres increases gradually;with the increase of surfactant dosage,the particle size decreases gradually.Nano-SnO₂ hollow spheres can be prepared by solvent thermal method and template method,respectively.The morphology of nano-SnO₂ hollow spheres prepared by solvent thermal method is better.The concentration of reactants,reaction temperature,reaction time and the amount of urea are the main factors of influencing the particle size of nano-SnO₂ hollow spheres.With the increase of reaction temperature,the particle size of hollow spheres decreases first and then increases.With the increase of reaction time,the particle size of hollow spheres increases first and then decreases.With the increase of urea dosage,the particle size of hollow spheres decreases gradually.In addition,SnO₂nanorods with uniform diameter distribution and good dispersion can be prepared by the solvothermal method.The concentration of reactant and the dosage of surfactant are the main factors of influencing the diameter of SnO₂ nanorods.With the increase of reactant concentration and surfactant dosage,the diameter of nanorods increases gradually.(2)In terms of electrochemical thermodynamics of nano-SnO₂:particle size and morphology have significant influences on the electrochemical thermodynamic properties of nano-SnO₂ electrode.With the decrease of diameter of nano-SnO₂,the standard electrode potentialE^o-and reaction equilibrium constantK^o-increase;temperature coefficient of standard electrode potential(?E ^o-/?T)_p,molar reaction Gibbs energy?_rG_m^o-,molar reaction entropy?_rS_m^o-,molar reaction enthalpy?_rH_m^o-and reversible reaction heat Q_r,m all decrease;and the logarithm of the equilibrium constant and other electrochemical thermodynamic quantities are linearly related to the reciprocal of diameter.When the diameter is the same,the electrode potential of the nano-SnO₂ solid spheres is larger than that of the nanorods,while the temperature coefficient,reaction Gibbs energy,reaction entropy,reaction enthalpy and reversible reaction heat of the nano-SnO₂ solid spheres are smaller than those of the nanorods.With the decrease of diameter,the influence of morphology is greater.In addition,the particle size and morphology also have a significant effect on the surface thermodynamic properties of nano-SnO₂electrode.With the decrease of diameter of nano-SnO₂,the molar surface Gibbs energy _m^sG,the molar surface entropy S_m^s and the molar surface enthalpyH_m^sall increase,and all are linearly related to the inverse of diameter.When the diameter is the same,the surface thermodynamic properties of nano-SnO₂ solid spheres are larger than that of nanorods,and the smaller the diameter,the more significant the effect of morphology.These experimental results are consistent with the corresponding thermodynamic equations of nanoelectrodes.(3)In terms of photocatalysis of nano-SnO₂:particle size and morphology have significant effects on the photocatalytic degradation of salt-based magenta by nano-SnO₂.For nano-SnO₂ with the same morphology and different diameters,the smaller the diameter,the better the adsorption performance and the better the photocatalytic performance.For nano-SnO₂ with the same diameter and different morphologies,the hollow spheres have the best photocatalytic performance,followed by the nanorods and the solid spheres.The smaller the diameter,the more significant the effect of morphology.The nano-electrochemical thermodynamics theory established in this paper can quantitatively describe the influence of particle size and morphology on the electrochemical thermodynamic properties of the nano-electrode,which can provide theoretical basis and guidance for the design,preparation,research and application of the nano-electrode.The preparation method of SnO₂ nanomaterials and the experimental results of the influence of particle size and morphology on electrochemistry and photocatalysis proposed in this paper can provide important reference for the preparation,research and application of SnO₂ nanomaterials.