Thermodynamic data and properties of polyoxometalate Na6V10O28

Abstract

Owing to their unique structure, polyoxometalates (POMs) are important compounds with both acidic and oxidizing properties that can be used in acid-catalyzed and redox-catalyzed reactions, as well as in medicinal chemistry and as functional materials. Vanadium-based polyoxometalate materials are an important class of POMs, in which Na6V10O28 is a common vanadium-based polyoxometalate produced by condensation and dehydration in acidic vanadium-containing solutions. However, the properties of the compound were reported extensively, but thermodynamic data and thermal stability were hardly available. In this study, Na6V10O28 material was synthesized by the liquid phase method and characterized by XRD, thermogravimetry, electron microscopy, and infrared analysis. The results show that the prepared material is Na6V10O28·18H2O and its decomposition product was Na5V12O32. The thermodynamic data of Na6V10O28. nH2O and Na5V12O32 such as heat capacity, entropy, and enthalpy were calculated by the NKR combined with drop calorimetry. Finally, the obtained data were applied to equilibrium thermodynamic calculations for reactions related to Na6V10O28, including condensation reactions, ammonium salt precipitation, thermal decomposition reactions, and hydrolysis precipitation. The results can be used for theoretical calculations of thermodynamic reactions related to Na6V10O28 and Na5V12O32.