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

Convenient and reliable sulfide ion (S2-) detection is necessary due to its harmfulness. Herein, a new colorimetric sensing platform for S2- 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 S2-, a simple and sensitive colorimetric method for S2- 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 S2- among some common cations and anions, and it was successfully applied in the real water samples.