The Effects Of Morphology And Particle Size On Electrochemical Thermodynamic Properties And Photocatalytic Performance Of Nano-TiO₂

Nano-TiO₂is widely used in sensors,lithium-ion batteries,supercapacitors,photocatalytic degradation of organic pollutants and other fields due to its relatively excellent electrochemical properties and photocatalytic performance.At present,the mechanism and law of the influence of morphology and particle size on nano-TiO₂are not clear.Therefore,it is of great theoretical significance and practical value to study the influence law and mechanism of morphology and particle size on the electrochemical properties and photocatalytic performance of nano-TiO₂.In this paper,based on the theory of reaction thermodynamics of nano system,the characteristic length and shape parameters are introduced,and then the generalized thermodynamic relations of electrode potential,temperature coefficient,equilibrium constant,Gibbs energy,reaction enthalpy,reaction entropy and reversible reaction heat with morphology and particle size of nano electrode made of nano particle are derived.The effects of morphology and particle size on electrode potential,reaction equilibrium constant,temperature coefficient,Gibbs energy,reaction enthalpy,reaction entropy and reversible reaction heat were discussed.In the experiment,the preparation of nano-TiO₂was studied by hydrothermal method,and the influence of hydrothermal temperature,hydrothermal reaction time and the amount of mixed solvent on the morphology and particle size of the product was studied.Then,the nano-TiO₂with different morphology and particle size was prepared,and the scanning electron microscopy（SEM）and X-ray powder diffraction（XRD）was used to characterize the crystal form,composition,morphology and particle size of the prepared nano-TiO₂.Then,the prepared nano-TiO₂with different morphology and particle size was assembled into nano electrode,and the electrode potential at different temperatures was measured by potentiometer,then the standard electrodepotential,temperature coefficient of electrode potential,Gibbs free energy,equilibrium constant,reversible reaction heat and other electrochemical thermodynamic quantities of nano-TiO₂electrode were obtained,and the effects of particle size and morphology on the electrochemical thermodynamic properties of nano-TiO₂were obtained and compared with the theoretical relationship formula.Finally,the prepared nano-TiO₂with different morphology and particle size was used as a photodegradation catalyst to study performance of photocatalytic degradation of rhodamine B under ultraviolet light.The effect of particle size and morphology on the photocatalytic degradation of Rhodamine B by nano-TiO₂was obtained.Through theoretical and experimental research,the following conclusions can be drawn:（1）Generalized thermodynamic theory of nanoelectrodesBy introducing characteristic length and shape parameters,generalized thermodynamic equations suitable for nano-electrodes with different morphologies and different particle sizes can be derived;these equations show that morphology and particle size have a significant effect on the electrochemical thermodynamic properties of nano-electrodes;And these equations can describe the quantitative relationship between the standard electrode potential,temperature coefficient,electrode reaction thermodynamic properties and reversible reaction heat of nanoelectrodes and their morphology and particle size.（2）Preparation of nano-titanium dioxideUsing hydrothermal method,by controlling the experimental conditions,linear nano titanium dioxide with diameters ranging from 30 nm to 100 nm and spherical nano titanium dioxide with 20 nm to 40 nm can be prepared.In the preparation of linear titanium dioxide,the amount of reaction medium increases,the diameter of the prepared nanowires increases,and the hydrothermal temperature and the concentration of the reaction medium have a greater influence on the morphology of the product.When preparing spherical nano titanium dioxide,the lower the proportion of ethanol in the mixed solvent,the smaller the particle sizes of the product.In addition,octahedral nano titanium dioxide with an average side length ranging from 80 nm to 170 nm can also be prepared by a two-step hydrothermal method.Among them,the lower the concentration of urotropine,the smaller the side length of the product,and the temperature of hydrothermal reaction and the amount of intermediates have a great influence on the morphology of octahedral nano-titanium dioxide.（3）Effects of morphology and diameter on the electrochemical thermodynamics of nano-TiO₂For a certain morphology（linear,spherical and octahedral）of nano-titanium dioxide,the average diameter has a significant effect on its electrochemical thermodynamics:when the average diameters of nano-titanium dioxide decreases,the standard electrode potential and reaction equilibrium constant increase,while the temperature coefficient of standard electrode potential,electrode reaction thermodynamic properties and the reversible heat of reaction decreases as the average diameter decreases.In addition,logarithm of equilibrium constant and other electrochemical thermodynamic quantities all have a good linear relationship with the reciprocal of the average diameters.These influence laws are consistent with theoretical analysis.The morphology of nano-TiO₂has a significant influence on its electrochemical thermodynamics:when the average diameter is the same or similar,the order of standard electrode potential is octahedron>spherical>linear,and the magnitude of Mohr Gibbs free energy of electrode reaction is linear>spherical>octahedral.The order of temperature coefficient of standard electrode potential,reversible reaction heat and other electrochemical properties is linear>spherical>octahedral.This is mainly due to the different morphology parameters and surface tension,which leads to different electrochemical properties of different morphology.（4）Effects of morphology and diameter on the degradation of rhodamine B by nano-TiO₂under UV lightWhen the morphology is the same,the photocatalytic degradation rate increases as the average diameter decreases.The order of photocatalytic degradation rate of nano-titanium dioxide with different morphologies is:octahedron>linear>spherical.The generalized thermodynamic theory of nanoelectrodes established in this paper and the influence of particle size and morphology on electrochemical thermodynamic properties and catalytic performance have important guiding role and reference value for the research and application of nanomaterials in related fields.