| In recent years,along with the rapid development of nanotechnology,magnetic nanomaterials have attracted extensive attention in the fields of catalysis,environmental adsorption,biomedicine,etc.due to their unique magnetic responsiveness and good biocompatibility.At present,the most reported magnetic nanomaterials are zero-dimensional Fe3O4 nanoparticles,which have the advantages of easy synthesis and controllable scale,but the exposed Fe3O4 nanoparticles have higher surface energy,which leads to easy agglomeration and restricted application.Moreover,the zero-dimensional Fe3O4 nanoparticles themselves have a lower theoretical saturation magnetization,and the saturation magnetization becomes lower after surface functional modification,resulting in poor magnetic response property to the external magnetic field.Therefore,it is of great scientific significance to develop a new type of magnetic nanomaterials with high saturation magnetization.In this article,a new kind of magnetic nanomaterial with high saturation magnetization was developed:one-dimensional Fe-Fe2O3 magnetic nanochains(NCs).In order to expand the application range of the magnetic nanochains,we use two polymers(polyphosphazene and polydopamine respectively)to functionalize the Fe-Fe2O3 nanochains.Two kinds of high-magnetic nanocomposites with core@shell structure were constructed.Based on the chemical structure of the modifier,the in-situ loading of nickel hydroxide nanosheets and noble metal Pd nanoparticles was realized respectively on the surface of the composites.And the bifunctional nanostirrers with high magnetic response property and catalytic activity were finally prepared.At the same time,we also accidentally discovered a method of environmentally friendly room temperature synthesis of a-Ni(OH)2 nanosheets with high specific surface area,and studied its formation mechanism and application in supercapacitor electrode materials.The main contents are summarized as follows:(1)One-dimensional Fe-Fe2O3 magnetic nanochains were prepared by simple one-step method with ferric chloride and sodium borohydride as raw materials and water/cyclohexane as solvent under the aid of mechanical agitation.The results showed that the Fe-Fe2O3 magnetic nanochains was about several micrometers in length and 40-60 nm in diameter,and the magnetic performance test showed that its saturation magnetization was up to 130.1 emu g-1 at room temperature,which showed good magnetic response property to the external rotating magnetic field.In this study,the Fe-Fe2O3 nanochains could catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine(TMB)in the presence of H2O2 and accelerate mass transfer for the hydrogenation of methylene blue(MB)in microscopic catalytic systems.The prepared Fe-Fe2O3 magnetic nanochains have the potential to be applied to the detection of hydrogen peroxide and as a nanoscale magnetic stirrer in the micro-catalytic reaction system.(2)Based on the high magnetic response Fe-Fe2O3 magnetic nanochains of the above synthesis,the crosslinked polyphosphazene(PZS)was coated on its surface to construct the Fe-Fe2O3@PZS magnetic nanocomposites with core@shell structure.In the experiment,the coating process of PZS was based on the in-situ condensation reaction of copolymer monomer hexachlorocyclotriphosphazene(HCCP)and 4,4'-sulfonydiphenol(BPS).With the help of the good structural properties of crosslinked PZS,we loaded nickel hydroxide nanosheets on the surface of Fe-Fe2O3@PZS to endow magnetic nanochains with catalytic activity,and then constructed bifunctional Fe-Fe2O3@PZS@Ni(OH)2 nanoscale stirring bars.The results showed that the crosslinked polymer PZS shell can protect the magnetic nanochains from strong acid and strong alkali corrosion and enhanced its stability.The saturation magnetization of Fe-Fe2O3@PZS@Ni(OH)2 at room temperature is as high as 103 emu g-1.By changing the loading process of nickel hydroxide,the controllable preparation of three kinds of microstructure Fe-Fe2O3@PZS@Ni(OH)2 nanochains can be realized.The apparent rate constant and turnover frequency(TOF)of the Fe-Fe2O3@PZS@Ni(OH)2-6 catalyst could be up to 0.60 min-1 and 20.0 h-1.In ten cycles of experiments,the conversion of 4-nitrophenol(4-NP)was still more than 90%.In addition,in the design of the micro-catalytic system test(catalytic hydrogenation of MB micro-droplets),the MB droplets can be completely faded within 20 s under the action of a rotating magnetic field.The prepared Fe-Fe2O3@PZS@Ni(OH)2 is expected to be used as excellent nanocatalyst and nanoscale magnetic stirrer in macroscopic and microscopical catalytic systems.(3)Based on the high magnetic response Fe-Fe2O3 magnetic nanochains of the above synthesis,the crosslinked dopamine(PDA)was coated on its surface,and the Fe-Fe2O3@PDA magnetic nanocomposites with core@shell structure were constructed.In the experiment,the coating process of PDA was carried out by in situ oxidative polymerization of dopamine hydrochloride monomer under alkaline conditions.By means of the reduction ability and chelating ability of the PDA itself,palladium chloride(PdC12)was reduced directly to palladium nanocrystalline,and the Fe-Fe2O3@PDA@Pd nanocatalyst with magnetic and catalytic properties was constructed.In the process of noble metal loading,we mainly analyze the role of PDA with the help of XPS and other characterization methods.The results showed that the hydroxyl groups on the surface of PDA will be oxidized into phenolic quinone during the reduction process,and the Pd nanocrystals obtained will be evenly distributed on the PDA surface.The saturation magnetization of Fe-Fe2O3@PDA@Pd was 105 emu g-1.For the 4-NP reduction and MB hydrogenation in presence of NaBH4,the rate constants of Fe-Fe2O3@PDA@Pd were up to 0.55 min-1 and 0.90 min-1,respectively.After six runs,the conversion of both reactions was still higher than 90%.This work clarifies the essence of the in-situ reduction of noble metal ions on the surface of PDA,and the high catalytic activity Fe-Fe2O3@PDA@Pd nanocatalysts were prepared.(4)In this section,based on the nickel hydroxide nanosheet loading scheme in section(2),a new method of environmentally friendly room temperature synthesis of a-Ni(OH)2 nanosheets was explored.In the experiment,we directly stirred the nickel chloride solution and the low concentration sodium borohydride solution and let the mixed solution stand for several hours.The nickel hydroxide nanosheets with high specific surface area under mild reaction conditions were prepared.The ability to catalyze the reduction of 4-NP was studied,and its electrochemical property was studied as supercapacitor electrode materials.The Brunauer-Emmett-Teller(BET)specific surface area of the ultrathin a-Ni(OH)2 nanosheets was calculated to be 393.4 m2 g-1,and the pore size distribution were cantered at micropores of about 1 nm and mesopores of about 35 nm.The as-prepared a-Ni(OH)2 nanosheets exhibited the highest specific capacitance of 2378.7 F g-1 at discharge current density of 1 A g-1,in a 2 mol L-i KOH aqueous solution.The a-Ni(OH)2 nanosheets show a specific capacitance retention of 71.7%after 3000 cycles.The as-obtained hierarchical a-Ni(OH)2 exhibited excellent catalytic performance in the reduction of 4-nitrophenol,with a reaction rate constant(k)of 0.33 min-1.In conclusion,starting from the design and preparation of one-dimensional magnetic nanochains,one-dimensional Fe-Fe2O3 nanochains were successfully prepared and their modification and functionalization were explored.Two kinds of bifunctional nanoscale stirrers have been obtained,which showed good magnetic response property and catalytic activity in macroscopic and microscopic catalytic systems.At the same time,a new method for preparing nickel hydroxide nanosheets at room temperature was also explored.The formation mechanism and electrochemical energy storage performance were studied.These studies have laid a good foundation for the construction of new magnetic nanomaterials and functional modification techniques. |
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