Cyclic voltammetry as a rapid descriptor of ligand-driven transformations and interfacial stability in MOF-based nanocomposites as a Fe3O4–MIL–88B(Fe) sample

Here, we introduce cyclic voltammetry (CV) as a rapid electrochemical screening tool for probing ligand-driven transformations and assessing the stability of MIL–88B(Fe) metal–organic framework and its Fe₃O₄-containing composites. The systems were investigated at pH 7.4 and 4.5 (PBS and NaOAc buffers) to simulate healthy extracellular tissue versus acidic tumor microenvironments, in the presence of ascorbic acid (AA) and humic acids (HA). At pH 7.4, both Fe₃O₄ and MIL–88B exhibit weak, irreversible reduction near −0.6 V (vs RHE), confirming structural stability and negligible iron solubilization. AA plays a dual role: it promotes Fe₃O₄ dissolution through reductive iron–ascorbate complexation, yet passivates the MIL–88B framework against iron leaching via surface ligand exchange. In contrast, HA moderates these interactions by attenuating redox current densities—an effect attributed to the formation of a hydrophobic interfacial barrier that restricts ion migration and suppresses desorption of iron–ascorbate species—consistent with recent insights into macromolecular organic layers under electric fields. Under acidic conditions (pH 4.5), all systems show increased electrochemical activity indicative of proton-assisted destabilization. Notably, the Fe₃O₄–MIL–88B composite exhibits superior resistance to degradation compared to its individual components. This stabilizing effect arises from restricted accessibility of the iron center and reduced ion diffusion within MOF pores, coupled with the active redox participation of Fe₃O₄ rather than its passive role as a conductive support. Overall, CV is established as a powerful descriptor of iron speciation and interfacial dynamics. By distinguishing between surface-confined ligand exchange, breathing (indirectly via diffusion kinetics), and bulk structural rearrangement, our work provides an efficient, predictive framework for screening functional nanomaterials as an alternative to protracted conventional stability assays.