Large scale fluorine-free synthesis of hierarchically porous iron(III) trimesate MIL-100(Fe) with a zeolite MTN topology

The hierarchically mesoporous iron(III) trimesate MIL-100(Fe) with a zeolite-MTN topology is known as an advanced functional material that is biocompatible. In this work, the large scale synthesis of MIL-100(Fe) has been achieved by hydrothermal reactions using suitable conditions without HF for the large scale synthesis. Although such conditions are narrow, the concurrent change of iron precursor and increase in the concentration of reaction mixture give rise to a synergetic effect leading to an increase in the crystallinity of F-free MIL-100(Fe). This method, combined with two purification steps (solvent extraction and chemical treatment with NH ₄F) leads to a highly porous F-free material obtained throughout a very high space-time-yield (>1700 kg/m ³ day). Possible formation mechanisms of MIL-100(Fe) under hydrothermal conditions have been proposed in terms of four steps such as hydrolysis, deprotonation, self-assembly, and polycondensation. The resulting material exhibits similar physicochemical properties to those of the one prepared in the presence of HF, except for a slight difference in sorption capacities of gases and liquid vapors corresponding to the difference of pore volume. Regardless of the use of HF, the purified MIL-100(Fe) possesses very high uptakes for both non-polar toluene and polar ethanol probe molecules due to the respective interactions with hydrophilic and hydrophobic sites in the framework. Finally, hydrophobicity measurements confirm that the dehydrated MIL-100(Fe) is more hydrophobic than conventional zeolite beta (SiO ₂/Al ₂O ₃ = 25) and commercial iron trimesate (Basolite F300) from BASF SE.