Size-dependent surface thermodynamic properties of nano-copper and its determination method by equilibrium constant

The surface thermodynamic properties play an important role in researching into the thermodynamics of nanoparticles involved in various chemical and physical processes. In this paper, the relations between surface thermodynamics properties, respectively, and particle size of nanoparticles were deduced. A new method of determining the surface thermodynamic properties of nano-copper by equilibrium constant was proposed. On the basis of the equilibrium constants of nano-copper with different particle sizes dissolved in sulfuric acid at different temperatures, the effect of particle size on the surface thermodynamic properties was investigated and the variation of surface tension with temperature was obtained. The influence regularities of size on the surface thermodynamic properties agree with the theoretical analysis. With the decrease in particle size, the molar surface Gibbs energy, the molar surface enthalpy and the molar surface entropy increase, and when the diameter exceeds 20 nm, the surface thermodynamic properties exhibit linear correlation with the reciprocal of diameter, respectively. The surface tension decreases with temperature increasing, and a linear relation between them is observed. This paper provides us a simple and reliable method to obtain the surface thermodynamic properties of nanoparticles for better understanding their thermodynamic behaviors in the chemical reaction, adsorption, melting, etc.