Ag_3PO_4微晶表面热力学函数的温度及形貌效应

Temperature and Morphology Effect on Surface Thermodynamic Functions of Ag_3PO_4 Microcrystals

在室温下采用离子交换法制备了四足状、立方体状和十二面体状Ag3PO4微晶及Ag3PO4块体,并进行了表征.以Ag3PO4微/纳米和块体材料热力学性质的区别为基础,结合化学热力学理论和热动力学基本原理,导出摩尔表面热力学关系式.在此基础上,采用原位微量热技术获取Ag3PO4的化学反应动力学信息和表面热力学函数,讨论了形貌和温度对表面热力学性质变化的影响.结果表明,四足状Ag3PO4的摩尔表面焓(Hsm)、摩尔表面Gibbs自由能(Gsm)和摩尔表面熵(Ssm)最大,立方体状次之,十二面体状最小;Hsm和Ssm随温度的升高而增大,Gsm则随温度的升高而减小.

Different morphologies of Ag3PO4 microcrystals, such as dodecahedrons, cubes, and tetrapods, were synthesized by ion-exchange method at room temperature. Based on the essential difference between thermodynamic properties of nano and bulk Ag3 PO4, the equations for acquiring molar surface thermodynamic functions of nano Ag3PO4 were derived via combining the basic theory of chemical thermodynamics with thermokinetic principle. According to the derived equations, molar surface thermodynamic properties such as molar surface Gibbs free energy, molar surface enthalpy and molar surface entropy of the prepared Ag3PO4 microcrystals were gained by in-situ microcalorimetry. Moreover, the temperature and morphology effect on these obtained surface thermodynamic functions were discussed. The results revealed that the surface thermodynamic functions of tetrapod Ag3PO4 were maximum, followed by cube and dodecahedron Ag3PO4. Along with the increase of the temperature, molar surface enthalpy and molar surface entropy increased, whereas molar surface Gibbs free energy decreased.