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Crystal structure, ion mobility, molecular mobility and phase transitions in microporous framework materials and layered metal (IV) phosphates and phosphonates

Inorganic ion exchangers, such as framework silicates and layered phosphates of tetravalent metals, are classes of materials with a wide variety of actual and potential industrial applications in the field of heterogeneous catalysis and electrochemical devices. The aim of this project is to obtain new materials with layered and three-dimensional framework structure and to investigate their crystal structure, the mobility of ionic and molecular guest species and the occurrence of phase transitions by using chemical and physical investigation techniques. The results will be interpreted in terms of the relation between the crystal structure and physico-chemical properties of the materials. As far as layered phosphates are concerned, the research will be focused on the development of dichalcogenide-zirconium phosphate composites and on the preparation of intercalation compounds of -zirconium phosphate with guests containing nitrogen and phosphorous basic centres. Apart from standard chemical characterization, the materials obtained will be investigated by solid state NMR (spin-spin and spin-lattice relaxation) and by combined ac/dc conductivity measurements under different conditions of temperature and relative humidity, in order to have information on ionic and molecular mobility of the species in the interlayer region. Regarding framework silicates, the main objectives at this stage of the project are a comprehensive study of the kinetics and mechanism of the phase transitions and structural changes in the framework silicates of the ANA structure type. The most important substances from the chemical and geochemical point of view were chosen as the subjects of investigation: analcime NaAlSi2O.6H2O, wairakite CaAl2Si4O12.2H2O, their dehydrated forms, and cation-exchanged forms based on the original analcime (thus having the same Al-Si distribution within the framework). The forms of special crystal chemical interest and potentially suitable for industrial applications : Li-analcime and NH4-analcime will be studied by various methods in a wide range of temperatures and pressures.

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Università degli Studi di Perugia
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