Fabrication Of One-dimensional Hierarchical Structured Nanofibers And Their Enzyme-like Catalytic Properties

One-dimensional(1D)nanomaterials are a type of special structures with nanoscale matter and a key branch of nanomaterial systems.In addition to the unique surface and interface effect,small size effect,macroscopic quantum tunneling effect,coulomb blocking effect and quantum tunneling,1D nanomaterials also exhibit the features of unique electron/mass transport capability and mechanical flexibility,providing them excellent chemical and physical properties.In recent years,1D nanostructures with hierarchical structures have been constructed with more excellent properties and have shown promising applications in energy conversion and storage,sensors,catalysis and biomedicine.Enzymes,as typical powerful biocatalysts,could efficiently catalyze a wide range of biochemical reactions in living organisms both in vitro and in vivo.Enzymes have been widely used in the transformation of biomolecules in industry,medicine and biology fields.However,the disadvantages of enzymes,such as high preparation and purification costs,high sensitivity to the environment,poor stability and difficult recovery,limit their broad applications.As alternatives to natural enzymes,nanozymes have attracted widespread attention from researchers for their good stability and low preparation cost.However,the catalytic efficiency and specificity of nanozyme materials with a single composition and simple structure cannot meet the needs of practical applications.Therefore,it is urgent to prepare nanozyme materials with hierarchical structures and multiple components to achieve an enhanced catalytic performance to replace natural enzymes.In this thesis,we focus on the design and synthesis of 1D hierarchical structured nanofiber materials by combining different preparation techniques,such as electrospinning,hydrothermal synthesis,vapor deposition,chemical bath deposition,high-temperature carbonization,and calcination.The morphology and composition of the materials were detailed analyzed.The prepared 1D hierarchical nanofiber materials exhibited good enzyme-like catalytic properties.By evaluating the catalytic activities of the components in the materials,the results indicated that the synergistic effects among the components and the confinement effects brought by different nanostructures have great influence on the electron transport ability and mass transfer ability of the materials.The details are as follows:1.TiO₂ nanofibers with smooth surface and homogeneous morphology prepared by electrospinning and calcination processes were used as the substrate to prepare TiO₂nanofiber-based hierarchical nanofibers through a hydrothermal method.Then,the enzyme-like catalytic properties of the nanofibers were investigated.Specifically,(1)TiO₂ nanofibers were used as the substrate and the MoS₂ shell was grown on their surface through a hydrothermal method,finally the TiO₂/MoS₂ core-shell hybrid nanofibers were obtained.In the enzyme-like catalytic property study,TiO₂/MoS₂ core-shell hybrid nanofibers exhibited excellent peroxidase-like catalytic,which was much higher than that of single TiO₂ nanofibers and MoS₂ nanosheets,due to the synergistic effect.We also investigated the effect of shell layer thickness on the peroxidase-like catalytic properties,and the results showed that the TiO₂/MoS₂ hybrid nanofibers with moderate shell layer thickness exhibited the best peroxidase-like catalytic activity.Based on the excellent peroxidase-like activity of TiO₂/MoS₂ core-shell composite nanofibers,the colorimetric detection of glutathione was achieved with the detection limit as low as 0.05?M.(2)Further,TiO₂/MoS₂ hybrid nanofibers were used as the substrate and interfacial barrier to grow ultrafine CoFe₂O₄ nanoparticles on their surface via a hydrothermal method,and finally produced TiO₂/MoS₂/CoFe₂O₄ ternary hybrid nanofibers.The prepared TiO₂/MoS₂/CoFe₂O₄ ternary hybrid nanofibers exhibited better peroxidase-like catalytic activity than any single or two-component hybrid nanofibers,due to the interfacial interactions between MoS₂ nanosheets,TiO₂nanofibers and the synergistic effect with TiO₂,MoS₂ and CoFe₂O₄ components.Based on the excellent peroxidase-like catalytic activity of TiO₂/MoS₂/CoFe₂O₄ ternary hybrid nanofibers,a colorimetric sensing method of L-cysteine was developed with a detection limit of 0.13?M.2.Hollow metal oxide/polypyrrole(PPy)nanofibers with PPy as the shell layer and encapsulated metal oxide particles inside it were obtained.Then,the enzyme-like catalytic properties of hollow metal oxide/polypyrrole nanofibers were investigated.This section includes two parts:(1)Cu Fe₂O₄ nanofibers were firstly obtained via an electrospinning and calcination technique.Subsequently,Cu Fe₂O₄ nanofibers were used as a template and oxidant to grow a PPy shell layer on its exterior via a vapor deposition process and Cu Fe₂O₄/PPy hollow nanofibers were obtained.By regulating the reaction time,the obtained Cu Fe₂O₄/PPy hollow nanofibers exhibited fiber-in-tube structure.The fabricated hollow nanofibers with this novel structure showed good peroxidase-like and catalase-like activity.The peroxidase-like activity was 16.9,17.9and 5.7 times as high as that of single Cu Fe₂O₄ nanofibers,PPy nanotubes and commercial Fe₃O₄ nanoparticles.Based on its excellent peroxidase-like activity,an efficient method for the detection of ascorbic acid(AA)was developed with a detection limit of 0.5?M.Due to the good detection ability of Cu Fe₂O₄/PPy hollow nanofibers for AA,a total antioxidant capacity(TAC)sensor was developed and was used to evaluate the determination of TAC in six commercial beverages and vitamin tablets.(2)Ni Co₂O₄ nanofibers were obtained via an electrospinning and calcination process.Subsequently,Ni Co₂O₄/PPy hollow nanofibers were prepared by using Ni Co₂O₄nanofibers as a template and oxidant to grow PPy shell layer on its exterior via a vapor deposition process.By regulating the reaction time,a distinct hollow structure with a clearly PPy shell layer and etched Ni Co₂O₄ nanoparticles could be observed in the Ni Co₂O₄/PPy hollow nanofibers.Furthermore,a high-temperature thermal reduction technique was applied to treat the Ni Co₂O₄/PPy hollow nanofibers and then NiO/CoO/PPy hollow nanofibers were obtained.The prepared NiO/CoO/PPy hollow nanofibers exhibited good peroxidase-like activity and catalase-like activity.Based on the excellent peroxidase-like activity of NiO/CoO/PPy hollow nanofibers,a colorimetric assay of glutathione was achieved with a detection limit of 0.02?M.Finally,based on the excellent detection ability and selectivity of the NiO/CoO/PPy nanofibers-based colorimetric assay,the ability of detecting glutathione in serum with favorable recoveries was investigated.3.Taking NiO hollow nanofibers as the research object,the influences including the encapsulation of functional materials in tubes and surface heteroatom doping,on the enzyme-like catalytic properties were investigated.(1)Cu-C nanofibers with homogeneous morphology were prepared via an electrospinning and high-temperature carbonization techniques,then Ni(OH)₂ nanosheets were grown on the surface of Cu-C nanofibers via a chemical bath deposition.Subsequently,the obtained samples were calcined in air.During the calcination process,carbon from the substrate was removed,Cu and Ni(OH)₂ were converted to CuO and NiO,respectively.Finally,CuO/NiO hollow nanofibers were obtain.The CuO/NiO hollow nanofibers exhibited good peroxidase-like catalytic activity,which were much higher than that of single CuO and NiO hollow nanofibers.In view of their good peroxidase-like catalytic activity,a rapid and simple colorimetric assay for the detection of isoniazid was developed with a detection limit of 0.4?M.Based on the excellent detection ability and selectivity of the CuO/NiO nanofiber colorimetric detection system,the detection capability in real samples was also investigated.In the test for isoniazid in isoniazid tablets,the measured results were very close to the standard values.In the tests for isoniazid in serum,favorable recoveries were also achieved.(2)Carbon nanofibers with uniform morphologies were prepared by through an electrospinning and high-temperature carbonization technique,then Ni(OH)₂ nanosheets were distributed on the surface of carbon nanofibers via a chemical bath deposition method.Subsequently,the obtained samples were treated with potassium cobalt cyanide solution to replace part of the Ni atoms with cobalt atoms.Finally,the obtained cobalt-doped CNF/Ni(OH)₂ nanofibers were calcined in air.During calcination,the carbon inside the substrate was removed and Ni(OH)₂ was converted to NiO,finally the Co-doped NiO hollow nanofibers were prepared.The results of the enzyme-like catalytic properties showed that the cobalt-doped NiO hollow nanofibers presented good peroxidase-like catalytic activity,which was much better than that of the single NiO hollow nanofibers.Subsequently,the obtained cobalt-doped NiO hollow nanofibers were used to detect AA by using a colorimetric method with a detection limit of 7.7 n M.Moreover,based on the good detection ability of the cobalt-doped NiO hollow nanofibers of AA,the evaluation of TAC of three fresh fruit juices was achieved.In summary,a series of 1D hierarchical nanofibers were prepared and their enzyme-like catalytic properties were investigated.It was found that the synergistic effect among the components and the confinement effect from the confined structure can greatly improve the catalytic activity of the materials.By constructing 1D hierarchical nanostructures,An enhancement of catalytic efficiency is achieved,and ultimately a sensing platform of the bioassay under complex conditions is realized.