Thermochemical properties for a series of microporous borophosphates of M~I[ZnBP_2O_8] (M~I = Na, K, Rb, Cs)

摘要

Two pure microporous materials, Rb[ZnBP_2O_8] and Cs[ZnBP_2O_8], have been synthesized and characterized by XRD, FT-IR, DTA-TG techniques and chemical analysis. The molar enthalpies of solution of Rb[ZnBP_2O_8] and Cs[ZnBP_2O_8] (s) in 3 mol ? dm~(-3) HCl (aq), of Zn(PO_3)_2 (s) in (HCl + H_3BO_3) (aq), and of RbCl (s)/CsCl (s) in [Zn(PO_3)_2 + HCl + H_3BO_3] (aq) were measured by microcalorimeter at T = 298.15 K, respectively. With the incorporation of the previously determined enthalpy of solution of H_3BO_3 (s) in 3 mol ? dm~(-3) HCl (aq), together with the use of the standard molar enthalpies of formation for Zn(PO_3)_2 (s), RbCl (s)/CsCl (s), H_3BO_3 (s), HCl (aq) and H_2O (l), the standard molar enthalpies of formation of-(3198.5 ± 1.2) kJ ? mol~(-1) for Rb[ZnBP_2O_8] and-(3212.7 ± 1.2) kJ ? mol~(-1) for Cs[ZnBP_2O_8] at T = 298.15 K were obtained on the basis of the appropriate thermochemical cycle. In addition, the molar enthalpy of formation of-(2944.4 ± 1.2) kJ ? mol~(-1) for [ZnBP_2O_8]~- has also been estimated by a group contribution method, which can be used to predict the △_f H_m~θ of the other similar borophosphates. Moreover, these data have been further used to compare the thermodynamic stability of this series of borophosphates.