Effects Of Morphology And Particle Size Of Nano-CeO₂ On Adsorption And Photocatalytic Properties

Due to nano-effects,nanomaterials usually exhibit unique adsorption and photocatalytic properties that are different from the corresponding bulk materials,which are decided by the morphology and particle size of the nanoparticles that make up the nanomaterial.However,the influence of particle size and morphology on adsorption and photocatalytic properties is still not fully understood,which seriously restricts the researches,applications and developments of nanomaterials.Therefore,taking the adsorption and photocatalysis on nano-Ce02 as a system,the effects of particle size and morphology on adsorption and photocatalytic properties were studied theoretically and experimentally.Firstly,spherical and linear nano-Ce02 with different particle sizes were prepared by hydrothermal/solvothermal method,and XRD and SEM were applied to characterize the morphology and particle sizeSecondly,in terms of adsorption theory,by defining the chemical potential of the nanoparticles before adsorption and the products after adsorption,the shape parameters are introduced,the general formulae of adsorption thermodynamic properties for nanoparticles with different shapes(linear or spherical,cubic,regular octahedron and other regular polyhedrons)were derived,and the influencing regularities and mechanisms of particle size and morphology on adsorption thermodynamic properties were discussed.Experimentally,the effects of nano-Ce02 with different particle sizes and different morphologies on the adsorption thermodynamic properties of Congo red were studied and compare with the theoretical relationship.Finally,in terms of photocatalysis,the effects of particle size and morphology on photocatalytic degradation of Rhodamine B by prepared spherical and linear nano-Ce02 were studied.Through research,the following conclusions are drawn:(1)Spherical nano-CeO2 was prepared by solvothermal method,during the preparation process,the concentration of Ce(NO3)3-6H20,the temperature and time of the reaction all had a certain influence on the particle size;the linear nano-Ce02 with different diameters can also be prepared by hydrothermal method,during the preparation process,the concentration of cerium source(CeCl3·7H2O)and the amount of ammonia were found to be the key factors to form the morphology of the nanowire,the volume of CeCl3·7H20 solution is the key factor to control the diameter.(2)The particle size and morphology have great influences on the thermodynamic properties of nano-Ce02 adsorption.For spherical/linear nano-CeO2,with the increase of particle size,the standard adsorption equilibrium constant decreases,while the standard molar adsorption Gibbs free energy,standard molar adsorption enthalpy and standard molar adsorption entropy decrease,ln K???adsGm???adsHm? and ?adsSm? showed a good linear relationship with the reciprocal of particle size,respectively.By comparing the adsorption thermodynamic properties of spherical and linear nano-CeO2,the results show that the adsorption equilibrium constant follows the rule:spherical>linear,The standard molar Gibbs free energy,standard molar adsorption enthalpy and standard molar adsorption entropy all follow the following rules:linear>spherical,and the smaller the particle size,the more significant the influence of morphology.When the particle size is extrapolated to infinity,the thermodynamic properties of the adsorption of different morphologies will accumulate to a point.These experimental results are consistent with the above thermodynamic theoretical relations.The mechanism of influence of morphology and particle size on thermodynamic properties of adsorption are that lnK? and ?adsGm? is influenced by the molar surface area and the difference between the surface tension before and after the adsorption,?adsSm? by the molar surface area and the difference in temperature coefficient of surface tension,?adsHm? by the molar surface area,the difference between the surface tension before and after adsorption and the difference between the temperature coefficient of surface tension before and after adsorption.(3)Particle size and morphology have great influences on adsorption and photocatalytic properties of nano-CeO2.For spherical/linear nano-CeO2,in the dark adsorption stage,the adsorption rate and adsorption rate constant of nano-CeO2 adsorbed Rhodamine B increased gradually with the decrease of nano-CeO2 diameter.In the photocatalytic reaction stage,the photocatalytic degradation rate and catalytic rate constant of nano-CeO2 photocatalytic degradation of Rhodamine B increased with the decrease of particle size.For nano-Ce02 of different morphologies,the order of adsorption rate,adsorption rate constant,photocatalytic degradation rate and photocatalytic degradation rate constant is:spherical>linear.This paper built the nano-adsorption theory and it can well explain the mechanism and essence of the effect of particle size on the thermodynamic properties of nano-adsorption.The nanoadsorption theory,the influencing regularities and mechanisms of shape and particle size on the adsorption and photocatalysis of nanoparticles can provide important references for the designs,preparations and applications of nano-adsorbed materials and nano-catalysts.