Ionothermal synthesis and characterisation of Mn-, Co-, Fe- and Ni-containing aluminophosphates

Metalloaluminophosphates (MAPOs) containing different metal ions (Mn3+, Mn2+, Co2+, Fe2+ or Ni2+) were synthesised in ionic liquids to investigate the effect of changing ionic liquid structure, reaction time, the nature of metal ions, and the initial metal/Al as well as F/Al ratios. A combination of XRD, C-13 CP MAS NMR, SEM images, Volhard titration, UV-Vis, thermogravimetric and nitrogen sorption measurements were performed to characterise the resulting MAPOs. The AFI framework of manganese-containing aluminophosphate (MnAPO) was prepared in an efficient way using MnF3 in 1-butyl-3-methylimidazolium bromide ([C-4 mim]Br) as both solvent and structure-directing agent (SDA). It was found that the resulting framework type can be altered by changing the ionic liquid's structure (cation, anion or alkyl chain) and this also influences the manganese content in the framework. Furthermore, tetramethylammonium fluoride ([Me4N]F) was employed as both mineraliser and co-SDA in the presences of [C-4 mim]Br for the formation of Mn-, Fe-, Co- and NiAPOs. The resulting framework type is dependent on the amounts of [Me4N]F and the nature of metal precursor, and as a result, the LTA, the SOD or a mixture of two framework types was obtained. The extent of substitution of metal atoms is directly dependent on the initial [Me4N]F/Al ratio, and metal cation (Fe2+ > Ni2+ > Co2+ > Mn2+) employed. The presented study leads to the first description for the ionothermal synthesis of MnAPO (CHA or LTA) and NiAPO (LTA), and offers efficient synthesis compared to previously reported ionothermal or hydrothermal methods.