Ultrathin binary MOF nanozyme with boosted activity via introduction of active iron sites for detecting sulfide ion

Convenient and reliable sulfide ion (S^2-) detection is necessary due to its harmfulness. Herein, a new colorimetric sensing platform for S^2- was established based on the binary NiFe metal-organic framework (MOF) nanozyme. The tremella-like NiFe MOF with ultrathin nanosheets was synthesized via introduction of active Fe sites in the Ni MOF by a rapid microwave-assisted method just in 11 min. The ultrathin NiFe MOF exhibited 2.8-fold higher peroxidase-like activity and 42.5-fold higher affinity to H₂O₂ than the Ni MOF, which could efficiently catalyze the decomposition of H₂O₂ into hydroxyl radicals (•OH) and superoxide anion radicals (O₂^•−) for the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB). The DFT study reveals that the dissociation energies of H₂O₂ and adsorption energies of reactive oxygen intermediates on Fe sites are more negative than those on Ni sites, proving the crucial role of Fe sites in the elevated peroxidase-like activity of NiFe MOF. By taking advantage of the unique redox reaction between H₂O₂ and S^2-, a simple and sensitive colorimetric method for S^2- was proposed based on TMB/H₂O₂/NiFe MOF system with a wide linear range of 0.5 – 60 μM and a low detection limit of 28 nM (3σ). The proposed NiFe MOF-based colorimetric method exhibited good selectivity to S^2- among some common cations and anions, and it was successfully applied in the real water samples.