Thermodynamic Parameters Evaluation of - and -cages in Na+, Ba2+, Fe3+, Co2+, Ni2+ and Cu2+ Exchanged Zeolite a Using Quantum Mechanical Theory and Fermi Dirac Statistics

The aim of present paper is to investigate the effects of non-framework cations, their hydration capacity and the role of phonons (acoustical and optical) on the thermodynamic characteristics of Type-A zeolite using Quantum mechanical theory and Fermi Dirac Statistics. This study is motivated by the lack of an accurate measurement capability of thermodynamic properties of zeolites by the existing methods reported in literature, that is why we have suggested the quantum mechanical and Fermi Dirac statistical approaches. Thermal analysis data for zeolite samples were obtained by thermogravimetric and differential thermal analysis (TG-DTG) technique at a heating rate of 10 K min–1 in order to evaluate the desorption behavior of water. The results showed that the thermal stability of these samples was found to be dependent mainly on the electropositive non-framework cations. Meanwhile, on the basis of thermodynamic parameters, the sizes of α- and β-cages in Na-A and its derivative zeolite were calculated using Fermi Dirac Statistics. Thereafter, semi-quantum effects (logarithmic behavior) of specific heat, entropy and enthalpy were observed in all samples as manifestations of the production of phonons due to gaining of thermal energy. As a result, Debye temperature would increase due to localization of heat energy in the Brillouin zone, and the calculated specific heat capacities showed almost no changes after cation exchange. However entropy and enthalpy first exceeds NaA in Ba2+, Ni2+ and Cu2+ and then decrease in Fe3+ and Co2+. These demonstrations indicated that Ba2+, Ni2+, Cu2+ Fe3+ and Co2+ cations influenced both the entropy and enthalpy as a result of the interaction of cations with the zeolite framework, which confirmed that the changes in the lattice mode were dependent on the increase or decrease in the electrostatic interactions between the cations and the framework zeolite.

Hamida Panezai, Abdul Nabi, Mohammad Yaqoob, Nusrat Munawar, Syed Haider Shah and Syed Mohsin Raza