Preparations And Applications Of Noble Metal Iridium Nanozymes

The noble metal iridium（Ir）has been used as a catalyst for various reactions due to its excellent stability,catalytic activity,and corrosion resistance.In recent years,Ir nanomaterials have been found to have enzyme-like activities,which not only exhibiting better catalytic activity than natural enzymes,but also possessing the advantages of simple preparation,good stability and wide applicability.However,there are not many reported types of enzyme-like activities of Ir nanomaterials,and studies on their preparation,structure,and catalytic mechanism are not comprehensive enough.Therefore,a series of new Ir nanomaterials were synthesized in this paper,and their enzyme-like activities,catalytic mechanisms and applications were studied in depth.The main contents are as follows:1、Based on previous reports on iridium nanoparticles（IrNPs）in the literature,we found that IrNPs prepared using coating agents with abundant surface functional groups and small molecular weight exhibit better enzyme-like activities.Therefore,we first attempted to prepare Tar-IrNPs by one-pot synthesis using L-tartaric acid（Tar）as the coating agent and NaBH₄ as the reducing agent.Through a series of characterizations,the successful preparation of Tar-IrNPs was demonstrated.Tar-IrNPs have oxidase-like,peroxidase-like,catalase-like properties,and also exhibit excellent laccase-like activity.Among them,laccase-like activity was first discovered among all IrNPs.Compared with natural laccase,Tar-IrNPs exhibit better catalytic activity and wider adaptability to conditions.The mechanism studies have shown that electron transfer is the reason why Tar-IrNPs exhibit excellent laccase-like activity.Tar-IrNPs can catalyze the oxidation of substrates o-phenylenediamine（OPD）and p-phenylenediamine（PPD）,accompanied by significant color changes.Based on color reaction,a colorimetric analysis method was established to detect OPD and PPD in this paper,which was successfully applied to the analysis of OPD and PPD in hair dye.As the reaction time prolongs,the polymerization products of OPD and PPD caused by oxidation can form precipitates and escape from the solution.Therefore,Tar-IrNPs can also be used for the removal of OPD and PPD organic pollutants in wastewater.2、In order to avoid the use of reducing agent NaBH₄ in the preparation of IrNPs,we tried to use ascorbic acid（AA）as the coating and reducing agent to synthesize AA-IrNPs through one-step hydrothermal method.By utilizing the strong reducibility of AA,the precursor Ir Cl₃solution can be reduced,while the abundant surface functional groups of AA enable the stable dispersion of IrNPs.After a series of characterization,the successful synthesis of AA-IrNPs was demonstrated.AA-IrNPs also exhibit oxidase-like,peroxidase-like,catalase-like,and laccase-like activities.Mechanism studies have shown that electron transfer is indispensable in the catalytic reactions of AA-IrNPs oxidase and peroxidase-like enzymes.Compared with other types of IrNPs,it was found that AA-IrNPs exhibit more excellent oxidase-like activity and can selectively catalyze the oxidation of lactic acid to pyruvate.The reaction can occur under relatively mild conditions,with a conversion rate of up to 77%and no by-products produced.3、On the basis of the preparation IrNPs in the presence of reducing agents,we further explored the preparation of IrO₂ NPs and their enzymatic activity in the absence of reducing agents.By changing the reaction temperature and the acidity and alkalinity of the precursor Ir Cl₃ solution,IrO₂ NPs were prepared under different conditions using hydrothermal method.After a series of characterization,the successful preparation of IrO₂ NPs was demonstrated.It was found that IrO₂ NPs not only exhibit oxidase-like,peroxidase-like,and catalase-like activities,but also exhibit laccase-like activity.The laccase-like activity of IrO₂ NPs catalyzes the oxidation of dopamine,while the color of the reaction system also changes accordingly.Therefore,we have established a colorimetric method for rapid detection of dopamine,which has high sensitivity.