Synergistic bimetallic nanozymes of Ni/ZIF-8 and Cu/ZIF-8 as carbonic anhydrase mimics

The remarkable diversity of metal nodes and ligands, coupled with the extensive array of connection modes, enables the precise design and assembly of metal-organic frameworks (MOFs), which have garnered significant attention in the field of nanozyme. In this study, the synthesis of zeolite imidazole framework materials (ZIFs) with varying Zn2+ and Ni2+ or Cu2+ concentrations were investigated and regulated by methanol, aiming to mimic the CO2 hydration activity of carbonic anhydrase (CA). The materials were comprehensively characterized using TEM, XRD, FTIR, UV-Vis DRS, XPS, and subsequently the catalytic performance of the materials was assessed. The results demonstrated that the structural characteristics of bimetallic Ni/ZIF-8 and Cu/ZIF-8 were influenced by varying concentrations of metal ions. Notably, ZIF-8 doped with lower metal content exhibited enhanced stability, while a precursor containing nickel and copper ions exceeding 50% hindered the formation of the desired ZIFs, resulting in an unstable cluster structure. However, methanol can counteract the inhibitory effect of metal ions on the structure. The bimetallic synergies of doped metals in ZIFs CA mimics can simultaneously expedite both two rate-limiting steps in the CO2 hydration process. The esterase activity of ZIF-8 doped with a small quantity of Ni2+ or Cu2+ can be achieved at a level comparable to that of human carbonic anhydrase (hCA II) at 80 °C, along with remarkable catalytic performance and hydrothermal stability. Specifically, Cu66%/ZIF-8 exhibited an activity of 0.31 U·mg−1 at 25 °C, which was 2.31 times higher than that of ZIF-8, moreover, the esterase activity at 80 °C was approximately 2.21 times greater than that of ZIF-8 under the same condition. While the relative activity of Ni50%/ZIF-8 and Cu50%/ZIF-8 still exceeding 50% even after five repeated utilization cycles. The bimetallic Ni/ZIF-8 and Cu/ZIF-8 can be easily synthesized using a simple method, resulting in enhanced catalytic activity. Therefore, it holds great potential for future applications in CO2 capture.