Reactive gas atmospheres as a tool for the synthesis of MOFs: the creation of a metal hybrid fumarate with a controlled Fe/Al composition profile

Abstract

The use of reactive gas atmospheres is proposed here as a new tool to control the synthesis of MOFs. With the addition of Al to an Fe-fumarate synthesis medium (which produces the typical structure of MOF MIL-88A(Fe)), a hybrid Fe/Al-fumarate that exhibits the structure of MOF MIL-53(Al)-FA was obtained even though both metals could be identified in the resulting material by STEM-HAADF. The use of CO and O₂ atmospheres (6 bar) in the synthesis of both MIL-88A(Fe) and MIL-53(Fe/Al)-FA might accelerate their synthesis and give rise to a highly crystalline solid and to core–shell nanoparticles (190 ± 42 nm) with an Fe-rich core surrounded by an Al-rich shell, i.e., with a controlled Fe/Al atomic distribution. After pyrolysis the MIL-53(Fe/Al)-FA particles exhibited superparamagnetism while keeping some texture (244 m² g⁻¹vs. 862 m² g⁻¹ of the as-made material).