The enzymatic performance derived from the lattice planes of Ir nanoparticles

Iridium nanoparticles (IrNPs) have shown intriguing enzyme-like activities; however, the mechanism behind their versatile enzymatic behaviors is still elusive. A new kind of IrNPs stabilized with beta-cyclodextrin (CD) was prepared in this work, and these IrNPs show oxidase-like, catalase-like and peroxidase-like activities. Their catalytic performances were comprehensively studied both by experimental characterization and theoretical calculations. The obtained results were systematically compared with other previously reported IrNPs. It was found that the catalytic properties of the IrNPs are derived from the lattice planes. All the IrNPs could catalyze the degradation of H2O2 due to the presence of the Ir(111) plane, while only the IrNPs with the Ir(220) plane exhibit oxidase-like activity. First of all, a new mechanism for the catalase-like activity of IrNPs was proposed here. The adsorption of H2O2 on IrNPs induces the breakdown of its O-O bond to form OH radicals. The produced OH will then couple with another OH or H2O2, forming the key intermediate species (O or OOH) in the production of O-2. According to the energy diagrams of H2O2 decomposition on different Ir planes, we suggest that the catalase-like activity is intrinsic to the Ir(111) plane and is independent of other crystal faces or coating agents. In addition, the radicals (OH and OOH) generated on different Ir crystal planes show different stabilities and reactivities, which is responsible for the diverse peroxidase-like activities of IrNPs. Finally, the oxidase-like properties are derived from the Ir(220) plane, where the chemisorbed O-2 could accept one electron to generate superoxide species. The mechanism revealed in the present work should be helpful for understanding the catalytic role of the lattice planes of IrNPs, which may also be applicable to other metal nanozymes.

Automated summary

This study prepared a new type of IrNPs stabilized with beta-cyclodextrin, exhibiting oxidase-like, catalase-like, and peroxidase-like activities. The catalytic performances were studied through experimental characterization and theoretical calculations, revealing that the catalytic properties of IrNPs originate from lattice planes. The mechanism for the versatile enzymatic behaviors of IrNPs were proposed, shedding light on the catalytic role of lattice planes and providing insights for other metal nanozymes.