S-Doped Iron-Triazolate Metal–Organic Framework Nanozymes: Ligand-Engineered High-Efficiency Peroxidase Mimics

Metal–organic framework (MOF)-based nanozymes have aroused wide interest in biocatalysis. In this work, a kind of MOF-based nanozymes were fabricated through a ligand regulation strategy. First, an iron-triazolate (MET(Fe)) nanozyme with the Fe–N structure was synthesized by the solvothermal method. Then, different proportions of the sulfur-containing ligand were introduced by the the mixed-ligand growth method to obtain a series of S-doped MET(Fe) (S-MET(Fe)) nanozymes. The S-containing ligand would competitively coordinate with Fe instead of triazolate, forming a "–C–SOx" bond and thereby resulting in more oxygen defects. The investigation of the catalytic mechanism showed that the doping of S affected the catalytic activity center of Fe, resulting in the generation of medium-spin species of FeIII and more coordination defects, thereby enhancing its catalytic activity. As a proof of concept, the 1/3-S-MET(Fe) nanozyme with outstanding peroxidase-like activity was used in biosensing and in the elimination of bacteria. This study provides new ideas for the design and construction of highly active nanozymes.