Synthesis, Characterization, and Thermal Kinetics of Mixed Gadolinium: Calcium Heptamolybdate System

Abstract

Synthesis of mixed gadolinium calcium heptamolybdate (GdCaHM) system in silica gel medium using single gel single tube technique has been successfully achieved. The grown crystal exhibits various morphologies, which includes spherulites, multifaceted, and square platelets. The nature of the grown material was established by X-ray diffraction (XRD) studies. Fourier transform infrared spectroscopy (FTIR) study signifies the presence of heptamolybdate (Mo7O24) and water symmetry structure, whereas energy dispersive X-ray analysis (EDAX) establishes the stoichiometric of the grown crystal as GdCaMo7O24·8H2O. The thermal behaviour was studied using the thermoanalytical techniques, which include thermogravimetry (TG), differential thermal analysis (DTA), and differential scanning calorimetry (DSC). Results obtained on the application of TG based models, namely, Horowitz-Metzger, Coats-Redfern, and Piloyan-Novikova, suggest the contracting cylindrical model as the relevant model for the thermal decomposition of the material. The kinetic parameters, namely, the order of reaction (n), activation energy (E a), frequency factor (Z), and entropy (ΔS∗), were also calculated using these three models.

Spatially Guided Assembly of Polyoxometalate Superlattices and Their Derivatives as High-Power Sodium-Ion Battery Anodes

“…The chemical structures of the Mo 7 building block and its assemblies were investigated by Fourier-transform infrared (FT-IR) spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS) (Figure ). The FT-IR spectra of Mo 7 exhibit characteristic bands at 872 and 838 cm –1 , which are assigned to symmetric stretching of the octahedral MoO 6 subunits and symmetric/antisymmetric stretching vibrations of [Mo 7 O 24 ] 6– , respectively. − Additionally, bands appearing at 895 and 920 cm –1 are associated with the stretching vibration of Mo–O–Mo and terminal Mo–O t bonds, while the peaks at 1640, 1402, and 636 cm –1 are related to free H 2 O molecule, NH 4 + , and H 2 O vibration modes, respectively . For Mo 7 -Co and Mo 7 -Co-CTA assemblies, the stretching vibration bands of MoO 6 and Mo 7 O 24 6– remain unchanged, indicative of an intact structure of the Mo 7 constituents.…”