Influence of fluoride ions on the structure-directing effect of organic amine in the synthesis of aluminophosphate open-frameworks

Abstract

The crystallization behavior of the initial mixture with the composition of Al2O3:4.0P2O5:3.0 diethylene-triamine(DETA):xHF:153H2O was investigated at 180 °C, where 0⩽x⩽3. If x⩽1.8, three-dimensional open-framework aluminophosphate AlPO-CJ31 was obtained. If 2⩽x⩽3, a chain-like aluminophosphate(1) was obtained. The crystallization process of both compounds was investigated by means of powder X-ray diffraction(XRD) and the concentrations of Al and P in the liquid product during the crystallization process were analysed by means of inductively coupled plasma atomic emission spectroscopy(ICP-AES). The evolution of the coordination state of Al, P and F during the crystallization was monitored with 27Al, 31P and 19F MAS NMR technique. The influence of the fluoride ions and the source of fluoride ions on the structure-directing effect of DETA was discussed. It was found that the fluoride ions changed the crystallization direction of the initial mixture, i.e., the structure-directing effect of DETA, via altering the distribution or micro-structure of the inorganic fragments.