Substitutional Single Iron Atoms as Active Sites for Nitrophenol Reduction by the Mo₂C MXene

Etching of Mo₂Ga₂C using in situ generated HF to produce Mo₂C MXene leads to the generation of atomic vacancies that can serve as anchoring sites for Fe single atoms. High-angle annular dark-field scanning transmission electron microscopy (HAAD-STEM) shows the absence of clusters or nanoparticles. Data from extended X-ray absorption fine structure (EXAFS) regarding Fe coordination fit well with the distances and environment calculated with density functional theory (DFT) for the substitution of Mo by Fe single atoms in the MXene lattice. Computational data also indicate that incorporation of Fe in the Mo layer favors a surface free of functional groups and ready to interact with substrates. These theoretical insights correlate with the experimentally observed high catalytic activity of Fe single atoms on Mo₂C for nitroarene reduction by aqueous NaBH₄, a benchmark reaction in organic synthesis for evaluating heterogeneous catalysts. Activity data show that Fe single atoms on Mo₂C rank among the most active materials reported so far for this reaction.