Abstract:

Cubic nano-cuprous oxides, with four types of particle sizes ranging from 40 to 120 nm, were synthesized via a liquid-phase reduction method. The composition, morphology and structure of the nano-Cu₂O particles were characterized by X-ray diffractometry (XRD), Raman microscopy and field emission scanning electronic microscopy (FE-SEM). In-situ microcalorimetry was used to obtain thermodynamic information about the reaction between HNO₃ and bulk Cu₂O or nano-Cu₂O. The surface thermodynamic functions of cubic nano-Cu₂O were calculated by a combination of thermodynamic principle and kinetic transition state theory. We develop a thermodynamic model for the cubic nanoparticles based on the thermodynamic model of spherical nanoparticles without bore developed by XUE Yong-Qiang et al. The particle size and temperature effects of surface thermodynamic functions are discussed by comparing the theoretical model with the experimental results. The molar surface Gibbs free energy, molar surface enthalpy and molar surface entropy increased with decreasing particle sizes. Linear trends were found between the reciprocal of particle size and surface thermodynamic functions, which agreed well with the theoretical model for a cube. The molar surface enthalpy and molar surface entropy were increased with rising temperature, whereas the molar surface Gibbs free energy decreased. This work not only enriches and develops the basic theory of nano-thermodynamics, but also provides a novel method and idea for investigating surface thermodynamic functions of nanomaterials and their applications.

Key words: Surface thermodynamic function, In-situ microcalorimetry, Thermodynamic model, Particle size effect, Temperature effect, Cubic nano-cuprous oxide