Study On Enzyme-like Catalysis And Colorimetric Analysis Of Molybdenum Disulfide-based Nanozymes

Nanozymes have been widely used in the fields of energy,environment monitoring,biosensing,antibacterial,medical imaging and disease diagnosis,due to the advantages of high stability,low cost,facile preparation,and adjustable catalysis.As compared with natural enzymes,however,there are still some problems such as low catalytic efficiency and low specificity.Molybdenum disulfide（MoS₂）as a typical representative of transition metal chalcogenide nanozymes,has a graphene-like layered structure and excellent mechanical,thermal,optical and electrical properties,and is used in energy,catalysis,solid lubrication,biosensing and other fields.Aiming to address the problems above,in this dissertation,MoS₂has been chosen as the research object to be compounded separately with carbon-based materials or doped with non-metal or metal heteroatoms to yield the molybdenum sulfide-based nanozymes with different topological structures and catalytic performances.Moreover,a variety of colorimetric analysis methods have been further constructed for the rapid analysis of glutathione（GSH）,mercury ions(Hg²⁺),hydrogen peroxide（H₂O₂）,and glucose targets of medical and environmental importance.SWCNTs@MoS₂nanozyme with 2D/1D heterostructure has been fabricated by the in-situ growth of molybdenum disulfide nanosheets onto single-walled carbon nanotubes.The obtained materials were characterized by means of electron microscopy,XPS,and theoretical calculations.Combined with steady-state kinetic tests,the mechanism of SWCNTs@MoS₂ enhancing peroxidase catalysis was revealed.It was discovered that the 2D/1D interface coupling in the heterostructure provides more reactive sites.Moreover,SWCNTs@MoS₂ is beneficial to charge transfer and facilitates electron transfer between substrates due to the in situ recombination of 2D MoS₂ nanosheets and 1D SWCNTs.A SWCNTs@MoS₂catalysis-based colorimetric strategy was constructed through the competitive reaction between the substrate and GSH in the catalytic reaction system.Furthermore,it was further proposed for the quantitative analysis of GSH with the concentrations linearly ranging from 0.01 to 1000.0μM and limit of detection at 7.0n M.Besides,the feasibility of the developed colorimetric method was evaluated by monitoring GSH in real samples with high sensitivity.C@MoS₂ nanozymes with hollow nanotube structures were prepared by a hydrothermal method using molybdenum trioxide,cysteine and glucose as main raw material.It was discovered that the introduction of carbon could not only endow C@MoS₂ nanozyme with a hollow nanotube structure to increase the specific surface area,but also accelerate its electron transfer,thereby enhancing the oxidase catalytic activity of C@MoS₂.Especially,the introduction of mercury ions(Hg²⁺)can accelerate the generation of superoxide radicals by forming the C@MoS₂-Hg S complex through the strong Hg-S chelation in the catalysis reactions to further enhance its oxidase catalytic performance.A catalysis-based colorimetric analysis with C@MoS₂ nanozyme was thereby constructed for the quantitative analysis of Hg²⁺ions,showing linear responses to Hg²⁺in the range of 0.01-100μM with the limit of detection of 2.7 n M.MoS₂ nanosheets were firstly prepared by hydrothermal method,and then the plasma-assisted controllable doping of nitrogen（N）into MoS₂ nanosheets has been initially proposed resulting in efficient nanozymes nitrogen-doped MoS₂ nanozymes（N-MoS₂）.It was discovered that the resulting N-doped MoS₂ nanosheets could present dramatically enhanced peroxidase-like catalytic activities depending on the plasma treatment time.Covalent nitrogen doping can not only improve the surface wettability,conductivity and affinity between nanozymes and substrates,but also endow N-MoS₂ with a lower Fermi level than MoS₂,making it easier to transfer electrons.In addition,it was found that nitrogen doping was beneficial to generate more hydroxyl radicals,thereby enhancing the peroxidase-like catalytic performance of N-MoS₂.Therefore,a colorimetric detection method based on N-MoS₂ catalysis has been constructed for the detection of H₂O₂ with high sensitivity,showing the linear responses to H₂O₂in the range of 1.0-100μM with the limit of detection of 0.15μM.Iron-doped molybdenum disulfide nanozymes（Fe-MoS₂）were prepared by doping with Fe elements into MoS₂ nanosheets via the hydrothermal method.It was discovered that the resulted Fe-MoS₂ could display controllable catalysis activities depending on the Mo-to-Fe molar ratios,among which the highest one was achieved at 3/1 with catalysis performance over three folds higher than that of pristine MoS₂.The doping of Fe was studied by means of XRD,electron microscope and XPS,and the structure-activity relationship between its structure and properties was systematically clarified.On the one hand,the doping of Fe provides more catalytically active sites for the nanozyme,and acts as the electron transferring mediators to to facilitate electron transfer between nanozyme and substrates.On the other hand,the Mo-S site in Fe-MoS₂ might conduct the catalytic behavior of Fenton-like reactions to generate more hydroxyl radicals in the catalytic system,as confirmed by the free radical experiment.The greatly improved catalysis performances of Fe-MoS₂ nanozyme are thought to be resulted from the synergistic effects of the two catalytic pathways of the doped Fe and Mo-S sites.Furthermore,combined with glucose oxidase,the developed Fe-MoS₂ nanozyme based colorimetric method was demonstrated for glucose with a good linear response from5.0 to 2000μM.Finally,the feasibility of practical applications for the detection of glucose in real samples with a good recoveries from 97.5%to 106.0%,showing a good practical application.