Ir nanoparticles with multi-enzyme activities and its application in the selective oxidation of aromatic alcohols

An enzyme-like nanoplatform obtained from sodium citrate-modified iridium nanoparticles (Cit-IrNPs) was presented, which exhibits excellent peroxidase, catalase and oxidase like activities thanks to the large accessible surface area and high-index facets of the mono-dispersed nanoparticles. The morphology and structures of Cit-IrNPs were comprehensively characterized by TEM, HRTEM, XRD, IR and XPS. The surface chemistry of Cit-IrNPs reveals that the oxidase-like and peroxidase-like activities can be ascribed to the formation of O2¯ from the activation of dissolved oxygen on the high-index facets of IrNPs. The oxidase-like activity of Cit-IrNPs was further manifested by the oxidation of 33.3 mM aromatic alcohols in the presence of 3 mg/mL Cit-IrNPs in ambient conditions. Over 90 % conversion rates were readily obtainable in 10 h for all the tested alcohols with an initial reaction rate of ca. 20 μmol/h. More significantly, apart from the aldehydes no other byproducts were detected. The kinetic analysis of the enzyme mimic suggests the reaction follows a classical Michaelis-Menten model. The enzyme mimic also shows a good stability, as no obvious decrease in catalytic activity was observed after recycled use for 6 times. Furthermore, DFT calculation was employed to elucidate the reaction mechanism and it was found that the alcohol is initially bond to Ir(0) and subsequently forms Irδ+-alkoxide species and the carbonyl product. Meanwhile, the Irδ+-hydride species reductively eliminates O2¯ and returns back to Ir(0). To the best of our knowledge, this is the first report of metal nanomaterials which can effectively transform aromatic alcohols to corresponding aldehydes at ambient conditions without need of external energy input.