立方体纳米Cu2O表面热力学函数的粒度及温度效应

液相还原法合成了4种粒度在40-120 nm的立方体纳米氧化亚铜（Cu₂O）。利用X射线衍射仪（XRD）、显微拉曼光谱仪和场发射扫描电子显微镜（FE-SEM）对纳米Cu₂O的物相组成及形貌结构进行了表征。采用原位微热量技术实时获取纳米/块体Cu₂O与HNO₃反应过程的热动力学信息，结合热化学循环及动力学过渡态理论计算得到纳米Cu₂O的表面热力学函数。在薛永强等建立的无内孔球形纳米颗粒的热力学模型基础上，发展了立方体纳米颗粒的热力学模型。最后由理论结合实验结果分析了粒度和温度对表面热力学函数的影响规律及原因。结果表明，摩尔表面Gibbs自由能、摩尔表面焓和摩尔表面熵均随粒度减小而增大，且与粒度的倒数呈线性关系，这与立方体热力学模型规律一致；随着温度的升高，摩尔表面焓和摩尔表面熵均增大，摩尔表面Gibbs自由能则减小。本文不仅丰富和发展了纳米热力学基本理论，还为纳米材料表面热力学研究及应用提供了方法和思路。

Effects of Particle Size and Temperature on Surface Thermodynamic Functions of Cubic Nano-Cu2O

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.