Ionothermal synthesis of gallophosphate molecular sieves in 1-alkyl-3-methyl imidazolium bromide ionic liquids

Gallophosphate (GaPO₄) molecular sieves were ionothermally prepared in 1-alkyl-3-methyl imidazolium bromide ionic liquids (ILs) with alkyl chain length varying from 2 to 6 carbons for the first time. Three kinds of GaPO₄ materials such as GaPO₄-a, cloverite (denoted as CLO below) and GaPO₄-LTA were obtained, and their structures and morphologies were characterized by powder and single crystal XRD, SEM and multi-nuclear NMR. In the case of 1-ethyl-3-methyl imidazolium bromide ionic liquid, large single crystals of GaPO₄-LTA with well-defined octahedral morphology was obtained in both sealed (ca. 400 μm in size) and open vessels (ca. 300 μm in size). Ionothermal synthesis is an effective method for the preparation of large single crystal of molecular sieves. With the alkyl chain length of the ionic liquids increasing from 2 carbons to 6 carbons, the size of GaPO₄-LTA decreased sharply. The organic template cations in the as-synthesized GaPO₄-LTA crystals may have two different kinds of conformational structures. Fluorine plays a role of co-template along with organic cations of ILs in the synthesis of GaPO₄-LTA and CLO, while only GaPO₄-a was obtained in the absence of fluorine. The reaction temperature can also affect the structure of the final structure. In the reaction medium of 1-ethyl-3-methyl imidazolium bromide IL, GaPO₄-LTA was obtained at 180 °C, while CLO was obtained at 150 °C.