Abstract
The hydrothermal synthesis and both the chemical and structural characterization of a diamin iron phosphate are reported. A new synthetic route, by using n-butylammonium dihydrogen phosphate as a precursor, leads to the largest crystals described thus far for this compound. Its crystal structure is determined from single-crystal X-ray diffraction data. It crystallizes in the orthorhombic system (Pnma space group, a = 10.1116(2) Å, b = 6.3652(1) Å, c = 7.5691(1) Å, Z = 4) at room temperature and, below 220 K, changes towards the monoclinic system P21/n, space group. The in situ powder X-ray thermo-diffraction monitoring for the compound, between room temperature and 1100 K, is also included. Thermal analysis shows that the solid is stable up to ca. 440 K. The kinetic analysis of thermal decomposition (hydrogenated and deuterated forms) is performed by using the isoconversional methods of Vyazovkin and a modified version of Friedman. Similar values for the kinetic parameters are achieved by both methods and they are checked by comparing experimental and calculated conversion curves.
Highlights
In recent years, the structures and properties of open-framework transition metal phosphates have attracted the interest of many researchers because of their possible utilization in different areas such as catalysis, adsorption, ion exchange and battery electrodes [1,2]
This paper reports the hydrothermal synthesis of Fe(NH3)2PO4 with an adequate size of crystallites to address the first structural characterization of this material from single-crystal X-ray diffraction
The scanning electron microscopy (SEM) image of Fe(NH3)2PO4 displayed in Figure 1 suggests the morphology of the sample is constituted by fibres forming compact blocks, unlike polycrystalline phases [11,13]
Summary
The structures and properties of open-framework transition metal phosphates have attracted the interest of many researchers because of their possible utilization in different areas such as catalysis, adsorption, ion exchange and battery electrodes [1,2]. The possibility of different oxidation states and coordination geometries of iron means that iron phosphates exhibit interesting magnetic properties [6,7]. These properties, together with their biocompatibility, make them potentially usable as nanostructured carriers in nuclear medicine. This provides an alternative to lanthanide phosphates, hydroxyapatite or iron oxides (magnetite and maghemite), which have been extensively studied in the field of biomedical applications as nanoconstructs and can be used as core platforms for attaching medical radionuclides [8]. Without urea or at low urea concentrations, only FePO4·2H2O is formed and as the concentration of urea and the pH in the reaction media increase, the sequential formation of NH4Fe(HPO4), NH4Fe2(PO4)2(OH)·2H2O, and Fe(NH3)2PO4 take place
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