Fabrication Of Core-shell Heterostructured Nanofibers And The Investigation On Their Enhanced Synergistic Catalytic Activity

As one of the important branches of nanomaterials,one-dimensional nanomaterials possess the size effect,surface effect and quantum size effect of conventional nanomaterials,as well as their unique thermal stability,high efficiency electron transfer capability and strong mechanical properties.In recent years,researchers have found that one-dimensional structure combined with multi-component and topological structures?such as chain,core-shell,branch,etc.?can be used to obtain one-dimensional core-shell composite nanomaterials with more diverse functions and better properties than single-component and particle-shaped nanomaterials.Previous studies have shown that one-dimensional core-shell composite nanomaterials have shown their advantages and application prospects in conduction,solar cells,sensors,catalysis,lithium-ion batteries and other fields.In this paper,one-dimensional core-shell heterogeneous nanomaterials were constructed by combination of electrospinning,calcination,chemical bath deposition,hydrothermal and other means.The morphology,structure and composition of the materials were characterized in detail.It was found that the as-prepared one-dimensional core-shell heterogenous nanomaterials exhibited good performance in the field of enzymatic catalysis and electrocatalysis.Through the analysis of their catalytic behavior,it was proved that the synergistic effect of the components in the materials and the electronic transport ability of the materials were the two key factors affecting the catalytic performance of the materials.The details are as follows:1.Transition metal oxide-based core-shell composite nanotubes:First,Co-C composite nanofibers synthesized by electrospinning and calcination were used as base material,and then construct core-shell morphology with chemical bath method,following with a oxidation process,transition metal oxide-based core-shell composite nanotubes were obtained,and their enzymatic catalytic properties were studied as follows:?1?Ni?OH?₂ shell was grown on Co-C nanofibers with chemical bath deposition,and then calcined and oxidized at high temperature.After removing C from the substrate,Co₃O₄@NiO core-shell nanotubes were obtained.In the analysis of enzymatic catalytic properties,Co₃O₄@NiO core-shell nanotubes can catalyze the oxidation of TMB rapidly in the presence of hydrogen peroxide,and the catalytic activity is much higher than that of single-component nanomaterials,suggestting that by constructing core-shell nanotubes,the synergistic effect between components can be fully exerted and the catalytic performance of materials can be improved.The detection limit toward hydrogen peroxide and DA can reach 1.23?M and 1.21?M respectively.?2?Co₃O₄@CeO₂ core-shell nanotubes were also constructed by chemical bath deposition and calcination.The catalytic properties of these enzymes were analyzed with TMB-H₂O₂ catalytic system.It was found that the materials exhibited good affinity to both substrates during the reaction,and the interaction between components reduced the Fermi level of the materials and effectively promoted the transfer of electrons from TMB to H₂O₂,improving the reaction efficiency.In the detection of hydrogen peroxide,the detection limit can reach 1.20?M.When the reaction system is further applied to ascorbic acid?AA?detection,the detection limit is as low as 0.73 nM,revealing its broad application prospects in the detection field.2.C-based core-shell heterostructure nanomaterials have been constructed,which can effectively reduce the internal resistance of materials,promote electron transfer and improve the properties of materials.The detail is displayed as follows:?1?2-MI and Co²⁺was used as raw materials to construct nanosheets structure on the surface of Co-C composite,folling with a calcination process,Co-C@Co₃O₄core-shell nanofibers could be obtained.The ultra-thin shell structure contains abundant catalytic active sites.At the same time,the synergistic effect between components caused by core-shell heterostructure and the continuous electron transport channel formed by C substrate make the charge transfer more efficient in the catalytic reaction process.Therefore,Co-C@Co₃O₄ core-shell nanofibers show excellent activity in both enzymatic catalytic activity and electrochemical catalysis.The linear range of the standard curve ranged from 0.8 to 10?M?R²=0.9700?and the detection limit was as low as 0.64?M?S/N=3?in the experiment of detecting hydrogen peroxide with its enzyme-like catalytic ability.In the OER catalytic reaction,the overpotential required reach current density of 10 mA cm^-2 was reduced to 350 mV when using Co-C@Co₃O₄ core-shell nanofibers as catalysts,and the cycle stability was excellent.In conclusion,with appropriate design of material structure,Co-C@Co₃O₄ has become a multi-functional catalytic material with excellent performance.?2?CoS₂-C@MoS₂ core-shell heterogenous nanofibers were synthesized from Co-C composite nanofibers by one-step hydrothermal method,in which MoS₂nanosheets were coated on the surface of the fibers and meanwhile Co nanoparticles inside were sulfurized.The synergistic effect between components makes up the defect of poor conductivity of MoS₂ and exhibited excellent catalytic activity in HER and OER.The OER overpotential and HER overpotential required for current density at 10 mA cm^-2 are 391 mV and 170 mV.It shows that the appropriate design and integration of various functional materials can overcome the drawbacks and expand the function of materials.It is further confirmed that the effective exposure of active sites and the conductivity of materials are the key factors affecting the electrocatalytic performance,which is of great significance for the development of high performance multi-functional catalytic materials.3.Conductive polypyrrole?PPy?nanotube-based one-dimensional core-shell nanomaterials with rich pion electrons could promote electron transfer in materials and enhance catalytic performance of materials by introducing PPy.The details are as follows:?1?We prepared PPy nanotubes using PAN nanofibers as templates,and then we obtained PPy@a-Ni?OH?₂ core-shell nanotubes by hydrothermal growth of Ni?OH?₂ on its surface.Then the catalytic performance toward urea oxidation was analyzed.It was found that the catalytic capacity of urea oxidation was much higher than that of single component material,and the current density reached j_@0.6=20.79mA cm^-2 at 0.6 V.PPy nanotubes provide a stable and solid base for materials,at the same time,their conductivity makes up for the shortcomings of poor electronic conductivity of Ni?OH?₂,and the tubular structure is also conducive to electrolyte infiltration,further promoting charge transfer during reaction,so as to improve the catalytic performance of materials.It is also confirmed that the structure and composition of materials have great impact on the improvement of catalytic performance.?2?With chemical bath deposition,PPy@?-Ni?OH?₂-Pd core-shell nanotubes were obtained and their catalytic behavior toward the oxidation of ethanol and formic acid was investigated.During the oxidation of ethanol,its catalytic activity is much higher than that of PPy-Pd and?-Ni?OH?₂-Pd,and the current density reached 23.21 mA cm^-2.In the experiment of formic acid oxidation,the current density reached 16.33 mA cm^-2,which exceeded the catalytic performance of the comparative sample,and even exceeded the catalytic activity of commercial Pd-C.It is worth mentioning that in the stability test,the stability of both catalysts is better than that of commercial Pd-C,demonstrating that the combination of PPy@?-Ni?OH?₂ and Pd can effectively alleviate the deactivation of Pd in the catalytic process and provide a good foundation for its practical application.In summary,metal oxide-based,C-based and PPy-based core-shell heterogenous nanofibers were prepared and their catalytic properties in different fields were analyzed.It was found that the synergistic effect between the components,the exposure of active sites and the ability of electron transfer during the reaction were the key factors affecting the catalytic performance of the materials.By building one-dimensional core-shell nanofibers,the above factors can be comprehensively utilized to greatly enhance the catalytic ability of materials and provide new ideas for the development of new multi-functional materials.