Stability and kinetics of iron-terephthalate MOFs with diverse structures in aqueous pollutant degradation

Synthesized iron-terephthalate metal–organic frameworks (MOFs), MIL-101 and MOF-235, with contrasting morphologies are examined to elucidate the role of structural arrangement in catalytic aqueous pollutant degradation. MIL-101 demonstrates a larger pseudo-first order rate constant than MOF-235 (3.5 ± 0.2 mol_Fe⁻¹·s⁻¹ vs. 0.84 ± 0.07 mol_Fe⁻¹·s⁻¹) toward oxidation of methylene blue (MB) dye with excess hydrogen peroxide at ambient temperature, likely due to intrinsic differences in ligand coordination at their metal nodes. However, despite continued activity upon reuse, both MOFs undergo structural alterations resulting in formation of leached species active for MB degradation that have been obfuscated in previous studies. Detailed stability testing and ex situ characterization of recovered catalyst, examinations that remain underreported in Fe-MOF studies for pollutant oxidation, indicate that water plays a prominent role in the breakdown of these frameworks. Collectively, this work informs the interpretation and use of common Fe-MOFs for aqueous applications, relating material changes to observed reaction phenomena.