Preparation And Antibacterial Performance Of Cu,Pd Metal Cluster Nanozymes

In recent years,the types and numbers of bacteria have been increasing and have become a serious problem threatening human health.At present,the antibacterial agents that are widely used are mainly antibiotics.However,the misuse of antibiotics can lead to the development of bacterial resistance,which makes antibiotics no longer meet the demand for antibacterial agents.Therefore,the search for new types of antibacterial agents has become an urgent problem nowadays.Nanozymes is a class of nanomaterials with catalytic properties that mimic those of natural enzymes.Nanozymes with peroxidase-like activity or oxidase-like activity can catalyze the conversion of H₂O₂ or O₂ to reactive oxygen species（ROS）,thus inducing oxidative stress in bacteria and resulting in bacterial cell death.Based on this,the application of nanozymes in the field of antibacterial is a feasible strategy.Nanozymes have become a hot research topic due to their excellent enzyme-like catalytic performance and biological properties.Compared with natural enzymes,nanozymes have the advantages of strong catalytic performance,good stability and low cost.The discovery of single-atom nanozymes has focused the research in the field of nanozymes to the atomic scale.Compared to traditional nanoparticle nanozymes,the single-atom nanozymes have maximized atom utilization,which leads to stronger enzyme-like catalytic performance.In addition,the atomically dispersed active centers facilitate the regulation of the catalytic performance and the study of the catalytic mechanism.Currently,many important results have been achieved in the research on single-atom nanozymes,which have been widely used in cancer therapy,oxidative stress cell protection and analytical assays.However,the catalytic performance of single-atom nanozymes may be weakened due to the lack of adjacent catalytic sites in the reaction.Based on this,it is crucial to develop novel nanozymes with desired catalytic antibacterial properties at the atomic scale.In this dissertation,we developed a series of atomically dispersed metal cluster nanozymes using nanodiamonds@graphene（ND@G）with defect-rich structure as carrier.We systematically investigated the enzyme-like catalytic activity and antibacterial properties of the series of atomically dispersed metal cluster nanozymes,and further explored the structure-activity relationship at the atomic scale,laying the foundation for the development of nanozymes with desirable catalytic antibacterial properties.The main research contents of this dissertation are as follows.（1）We developed an atomically dispersed Cu cluster nanozyme（Cu₃/ND@G）using ND@G as carrier.The surface of ND@G carrier is rich in carbon defects,which is conducive to the dispersion of metal atoms.The Cu₃/ND@G nanozyme has atomically dispersed Cu₃ clusters as the active center,thus having maximum atom utilization.At the same time,the atomically dispersed Cu₃clusters structure facilitates the adsorption and activation of O₂.Notably,the oxidase-like catalytic activity of Cu₃/ND@G nanozyme is much higher than that of copper nanoparticles nanozyme（Cu-NPs/ND@G）and even higher than that of the reported copper single-atom nanozymes.The Cu₃/ND@G nanozyme can catalyze the decomposition of O₂to generate hydroxyl radicals（·OH）,which interact with bacterial cells and induce oxidative stress in bacteria,resulting in cell death.We selected Gram-positive bacteria Staphylococcus aureus（S.aureus）and gram-negative bacteria Escherichia coli（E.coli）as representative strains for antibacterial testing.The antibacterial test results showed that Cu₃/ND@G nanozyme has excellent catalytic antibacterial properties compared with Cu-NPs/ND@G and is an excellent catalytic antibacterial nanomaterial.（2）To further investigate the structure-activity relationship of the nanozymes at the atomic scale,we developed single-atom Pd nanozyme（Pd₁/ND@G）and atomically dispersed Pd clusters nanozyme（Pd_n/ND@G）by the deposition-precipitation method.In addition,we also prepared Pd nanoparticles nanozyme（Pd-NPs/ND@G）by the conventional impregnation method.Compared with Pd₁/ND@G nanozyme and Pd-NPs/ND@G nanozyme,Pd_n/ND@G nanozyme can not only provide adjacent metal atoms as catalytic sites,but also maintain the maximum atom utilization efficiency.In addition,a small amount of Pd-Pd coordination reduces the valence state of Pd and increases the electron density around the Pd site,which facilitates the adsorption and activation of O₂.Therefore,the atomically dispersed Pd clusters nanozyme has higher oxidase-like catalytic performance than single-atom Pd nanozyme and Pd nanoparticles nanozyme.The Pd_n/ND@G nanozyme can effectively catalyze the decomposition of O₂ to generate hydroxyl radicals（·OH）,resulting in bacterial death.The results of antibacterial experiments showed that the Pd_n/ND@G nanozyme had stronger catalytic antibacterial activity against both Gram-positive S.aureus and Gram-negative E.coli compared with Pd-NPs/ND@G and Pd₁/ND@G.The work in this chapter lays the foundation for the development of nanozymes with desired catalytic antibacterial properties.（3）To investigate the effect of the introduction of second component metal on the catalytic antibacterial properties of atomically dispersed metal cluster nanozymes,we designed and prepared an atomically dispersed Pd-Ce bimetallic clusters nanozyme（PdCe/ND@G）by co-deposition-precipitation method.The results showed that the introduction of second component Ce promoted the dispersion of Pd,while the presence of Pd likewise promoted the dispersion of Ce.The mutual promotion improved the catalytic performance of the PdCe/ND@G nanozyme.Importantly,the introduction of Ce provided electrons to Pd,which increased the electron density of the Pd active site,resulting in a stronger peroxidase-like catalytic activity of the PdCe/ND@G nanozyme.The results of TMB oxidation experiments and antibacterial experiments showed that PdCe/ND@G nanozyme have stronger peroxidase-like catalytic activity and antibacterial properties compared to monometallic palladium nanozymes（Pd/ND@G）and monometallic cerium nanozymes（Ce/ND@G）.The work in this chapter provides a new idea for the development of bimetallic nanozymes with desired catalytic antibacterial properties.