Amorphous porous Fe-BTC prepared via the post-synthetic metal-ion metathesis of HKUST-1

Abstract

“Defect engineering”, in which defects are intentionally introduced into metal–organic frameworks (MOFs) with the aim of functionalizing pores and modifying their size distributions, has recently attracted considerable interest. Unfortunately, the surface area of a MOF is inversely proportional to the number of defects, which is the main drawback associated with defect generation; consequently, amorphous MOFs are not very porous. Herein, we prepared Fe-BTC (BTC = 1,3,5-benzenetricarboxylic acid), a defect-rich, amorphous, but porous material, via the post-synthetic metal-ion metathesis (PSMM) of CuZn-HKUST-1 with Fe²⁺/Fe³⁺. Zn²⁺ is relatively weakly bound to BTC³⁻ and is easily replaced by Fe²⁺/Fe³⁺, whereas Cu²⁺ forms stable bonds that maintain the overall MOF structure during the PSMM. Subsequent oxidation of all Fe states to Fe³⁺ creates significant defects and disorder at metal nodes. While the resulting amorphous Fe-BTC is of similar porosity to Cu-HKUST-1, defects at its metal sites accelerate reactions involving Lewis acid catalysis.