The Effects Of Particle Size And Morphology On Adsorption And Photocatalytic Properties Of Nano-Bi₂O₃

Nano-Bi₂O₃ is a promising photocatalyst,and the particle size and the morphology of nano-Bi₂O₃ have great influence on its adsorption and photocatalytic properties.At present,the regularities of particle size and morphology of nano-Bi₂O₃ on the adsorption and photocatalytic degradation of basic fuchsin are still unclear.The effects of particle size and morphology on adsorption and photocatalytic properties of nanoparticles were studied theoretically and experimentally.In theory,through the adsorption kinetic and thermodynamic theories of spherical and linear nanomaterials,we studied the effects of particle size on adsorption kinetic parameters,standard equilibrium constants and thermodynamic properties of spherical and linear nanomaterials,respectively.By introducing morphology factors,the general relations of adsorption kinetics and thermodynamics of spherical and linear nanomaterials were obtained,and the influence of morphology on adsorption kinetics parameters,standard equilibrium constants and thermodynamic properties were studied,respectively.In experiment,we studied the effects of particle size and morphology of nano-Bi₂O₃ on its adsorption and photocatalytic degradation properties of basic fuchsin.The conclusions are as follows:(1)A series of spherical and linear nano-Bi₂O₃ with different particle sizes were prepared by solvothermal method and hydrothermal method,respectively.The type and dosage of alkali source,the dosage of surfactant and the volume of reactor have a certain influence on the particle size of spherical nano-Bi₂O₃.Among them,the particle size of nano-Bi₂O₃ prepared with potassium hydroxide as the base source has a small particle size.The particle size of the product decreases with increasing the amount of potassium hydroxide,decreases with increasing the amount of surfactant,and increases with increasing the volume of the reactor.For Bi₂O₃ nanowire,the concentration of nitric acid,the volume of nitric acid and the react time have a certain influence on the morphology of the product.Reaction time is the key factor influencing the diameter of the nanowire,and the diameter decreases with increasing hydrothermal time.(2)In terms of adsorption kinetics,for the two morphologies of nano-Bi₂O₃,the adsorption rate constant k increases with the decrease of particle size,while the adsorption activation energy Ea and the pre-exponential factor A decrease,and Ink,Ea and lnA show good linear relations with the reciprocals of particle size d-1,respectively.Under the same diameter,the k of spherical nano-Bi₂O₃ is larger than that of linear,while the Ea and the lnA of linear nano-Bi₂O₃ are larger than those of spherical.The difference of lnk of nano-Bi₂O₃ with the two morphologies is influenced by the surface tension and the morphology factor,the difference of Ea is also influenced by the surface tension and the morphology factor,and the difference of A is influenced by the temperature coefficient of the surface tension and the morphology factor.(3)In terms of adsorption thermodynamics,for the two morphologies of nano-Bi₂O₃,the standard equilibrium constant(?)increases with the decrease of particle size,while the standard molar adsorption Gibbs energy ?ads(?),the standard molar adsorption enthalpy ?ads(?)and the standard molar adsorption entropy ?ads(?)all decrease,and ln(?),?ads(?),?ads(?)and ?ads(?)have good linear relations with d-1,respectively.Under the same diameter,the In(?)of spherical nano-Bi₂O₃ is larger than that of linear,and ?ads(?),?ads(?)and?ads(?)of linear nano-Bi₂O₃ are all larger than those of spherical.The difference of In(?)and the difference of ?ads(?)of nano-Bi₂O₃ with the two morphologies is influenced by the difference in surface tension before and after adsorption and the morphologic factor,and the difference of ?ads(?)is mainly determined by the morphologic factor,and the difference of ?ads(?)is linfluenced by the difference in temperature coefficient of surface tension before and after adsorption and the morphologic factor.The molar surface Gibbs energy Gms,molar surface enthalpy Hms and molar surface entropy Sms of nano-Bi₂O₃ with different morphologies all increase with decreasing particle size,and Gms,Hms and Sms have linear relations with d-1,respectively.Under the same diameter,the Gms,Hms and Sms of linear nano-Bi₂O₃ are larger than those of spherical.With the decrease of diameter,the effect of morphology of nano-Bi₂O₃ on the surface thermodynamic properties is more significant.(4)In terms of photocatalysis,the degradation rate and degradation rate constant of the basic fuchsin by photocatalytic degradation of spherical and linear nano-Bi₂O₃ increase with decreasing diameter.At the same diameter,the adsorption rate,adsorption rate constant,photocatalytic degradation rate,and degradation rate constant of spherical nano-Bi₂O₃ are all larger than those of linear.Through the comparison of adsorption and photocatalytic kinetic orders,it is found that the step of adsorption is the speed control step of nano-Bi₂O₃ photocatalytic degradation of basic magenta.It has a certain guiding significance to provide a new way for improving the catalytic performance of photocatalysts.The adsorption kinetic theory and thermodynamic theory of nanoparticles in this paper can quantitatively and qualitatively reflect the influences of the particle size and morphology of nanoparticles on their adsorption properties.The experimental results are consistent with the theoretical analysis.The theoretical and experimental study can provide important theoretical guidance and experimental reference for the research and application of nano adsorbents and nano photocatalysts.