Research Into Effect Of Particle Size On Electrochemical Properties And Photocatalytic Activity Of Nano-ZnO

The preparation technology of nanomaterials has developed rapidly.Compared to its corresponding bulk material,nanomaterials have significantly different electrochemical properties and photocatalytic activity,which mainly depends on the particle size and morphology of nanoparticles.However,the effects of particle size and morphology on the thermodynamics properties and photocatalytic activity of nanomaterial are still imperfect.In this paper,nano-ZnO is studied as the research object,and the effects of particle size and morphology on its electrochemical thermodynamic properties and photocatalytic activity will be systematically studied.Preparation of nano-ZnO with different morphology and particle size.In this paper,the sol-gel method,hydrothermal method and complex-precipitation method are used to prepare spherical,rod-shaped and flower-like nano-ZnO with different particle sizes.The crystal structure,particle size and morphology of the products are characterized by XRD and SEM.The influence of preparation conditions on the particle size is discussed.The results show:In the experimental process of preparation of rod-shaped nano-ZnO by hydrothermal method,the concentration of PVP in the system mainly affected the average length and diameter of the nanorods,while the reaction time had a great influence on the morphology of the product;In the experimental process of preparation of flower-like nano-ZnO by complexation precipitation method,the concentration of Zn²⁺is an important factor affecting the morphology of the product,while the reaction ratio,reaction temperature and reaction time have certain effects on the diameter of the flower-shaped microspheres and the thickness of the nanosheets.Experimental study on the thermodynamics of nano-ZnO electrode reaction.Nano-ZnO with different particle sizes are made into nano-electrodes,and assembled into primary batteries.The electromotive force of the primary batteries at different temperatures is measured.According to the Nernst equation,the standard electrode potential of nano-ZnO is calculated,and the variation of the standard electrode potential with the particle size is obtained.According to the relationship between the standard electrode potential and the temperature,the temperature coefficient is obtained by fitting,and the relationship between the temperature coefficient and the particle size is obtained.The corresponding electrode reaction thermodynamic function is calculated from the standard electrode potential and temperature coefficient.The influence of particle size on the thermodynamic function of the electrode reaction is discussed.The results show that the particle size of the nano-ZnO has a significant effect on the thermodynamics of the electrode reaction.With the particle size of nano-ZnO decreasing,the standard electrode potential and the equilibrium constants of the corresponding electrode reactions increase,while the temperature coefficient,the molar reaction Gibbs energy,enthalpy and entropy decreases.All of these quantities are linearly related with the reciprocal of particle radius within the experimental range.Nano-ZnO photocatalytic performance test.The RhB is used as the target pollutant,and the nano-ZnO with different morphology and particle sizes are used as catalysts.The effect of particle size and morphology on the catalytic performance of nano-ZnO was studied.The results show that the particle size has a significant effect on the photocatalytic performance of nano-ZnO.With the decreasing of particle size,the catalytic degradation rate and the reaction rate increases.The effect of morphology on the photocatalytic performance of nano-ZnO is mainly reflected in the reaction rate,and the effect on the degradation rate is not obvious.When the size of the nanoparticle is approximately same,the catalytic rate sequence:flower-like>rod-shape.We speculate that may be the fact that flower-like ZnO is cross-linked into petals by many nanosheets,and self-assembled component layer structure,which increases the specific surface area of nano-ZnO,making the photocatalytic reaction easier.