| FePt low-dimensional nanomaterial has widely promising applications,because the nanomaterial shows good magnetic properties,electrocatalytic activities,and biocompability.The performances of FePt low-dimensional nanomaterial are related to its composition,crystal structure,size and shape.Therefore,controllable preparation technology has become a hot research topic in this field.The wet-chemical method has widely been used because of its facility,economy,and suitability for large-scale production.However,the surfactant,a mainly control parameter during the solution growth process,is affected easily by the synthesis conditions.It is difficult to obtain a general mechanism in the crystal growth process because the complex interaction of surfactant.How to obtain a new preparation path with good controllability and repeatability has been regarded as the critical bottleneck problem for the large-scale production and application of FePt nanomaterials.Searching for a novel control method,revealing its growth behavior and mechanism,and achieving stable and controllable preparation of FePt nanomaterials have become the key to the researchers in this field.Recently,the high magnetic field materials science(HMF-MS)is gradually recognized by researchers.The research works indicated that the HMF could be used to affect the liquid-phase growth process and to tune the morphology,arrangement and phase of products,through generating the Lorentz force,the magnetizing force,the magnetizing energy and the magnetic polarization interaction energy.In order to solve the bottleneck problem of current FePt preparation,a novel HMF-assisted wet-chemical synthesis method has been proposed in this dissertation.On the one hand,a new method with good controllability and repeatability could be developed to synthesize FePt low-dimensional nanomaterials.On the other hand,the growth behavior of FePt crystals under HMF would be studied,the influence mechanism of HMF on the nanoscale crystals growth in non-aqueous system and on the microstructure of low-dimensional nanomaterials would be clarified,and the gaps in this field would be filled.This work would provide the experimental data and basic theory for promoting the practical application of FePt nanomaterials.Based on systematic experimental research and theoretical analysis,the following results were obtained:(1)In the wet-chemical synthesis process of FePt nanoparticles,HMF refined the sizes by increasing the nucleation rates and decreasing the growth rates,tuned the shapes by affecting growth habits.At all stages of growing,by comparing the microstructures of FePt nanoparticles obtained under 0 T and 6 T HMFs,it was found that the application of a 6 T HMF showed no effects on the composition and phase,but tailored the shapes and sizes of FePt nanoparticles.At the nucleation stage,the HMF enhanced the nucleation rates by increasing the thermal decomposition rates of the precursors.This increase was insufficient to change the morphology of the product,but reduce the size.At the growth stage,the growth rates of FePt nanoparticles obtained under 0 T and 6 T HMFs,the growth distances and the volumes of FePt nanoparticles synthesis at different temperatures under 0 T and 6 T HMFs,and the growth distances and the volumes under various HMF strengths have been detected.The fitting results indicated that the application of the 6 T HMF decreased the diffusion growth rates through breaking the microscopic convection in liquid phase,reduced the reaction growth rates by magnetizing and decreasing of the surface energy.The reduction of the above two growth rates leaded to the refinement of the product sizes.Meanwhile,the HMF increased the precursor atoms deposited rates along the<100>easy magnetization axis through enhancing magnetocrystalline anisotropy energy,so the morphology of the product was regulated.(2)The morphology and size evolution laws and paths of the FePt nanoparticles under 0 T and 6 T HMFs were summarized.The empirical formulas for predicting the morphology and size,and for guiding controllable synthesis of FePt nanoparticles were obtained.The influences of chemical reagents on the growth distances of FePt crystals along<100>and<111>directions under 0 T and 6 T HMFs have been studied.Under the 6 T HMF,the influences of the reducing agent hexadecanediol(HDD)and the surfactant oleic acid(OA)with strong polarity on the growth habit of FePt crystals were same to that of 0 T.However,the effects of the surfactant oleylamine(OAm)with weak polarity and the solvent dibenzyl ether(DE)with non-polar were restrained.The growth distances of FePt nanoparticles(synthesizing for 60 minutes)has been provided through analyzing and summarizing the shapes and sizes evolution paths at 0 T and 6 T HMFs:L<100>,T,H≈[(16.20·mHDD+0.55·VOA+0.37·VOAm-3.4×10-2·VDE+0.22)3-1.3×10-2·(518-T)·H2]1/3·exp(6.6×10-4-0.30/T)L<111>,T,H≈[(50.60·mHDD+1.48·VOA+1.27·VOAm-7.0 ×10-2·VDE-5.16)3-9.8×10-2·(518-T)·H2]1/3·exp(6.3 ×10-4-0.28/T)where T is temperature,H is magnetic field strength,m and V are the mass and volume of chemical agents,respectively.Through the above two quantitative calculated formulas,the shape and size of the FePt nanoparticles could be predicted,and those two formulas could also be used to controllable synthesis of FePt nanoparticles.The contrast analysis showed that HMF decreased the size of FePt concave-cube nanoparticles.(3)HMF facilitated one-dimensional growth of FePt nanowires by enhancing the orientation attachment growth mechanism.A reasonable kinetic growth condition by assisting of HMFs was constructed,the nanorods with a content as high as 90%was obtained.The growing and assembling of FePt low-dimensional nanomaterials with different concentrations and sizes under HMF have been studied.The magnetic polarization interactions energy generated by HMF did not dominated the anisotropy growth of FePt nanoparticles,but enhanced the one-dimensional orientation attachment of FePt nanowires.Though reducing the initial growth size using HMF-assisting,then,removing the excess Fe(CO)5 by breaking condensing system to build a Pt-rich growth environment,finally,growing in the(100)-stable DE solvent without of HMF,the FePt nanorods were produced by this kinetic growth method.The maximum content of nanorods in the products was about 90%when the HMF strength was 6 T and the removing temperature was 110℃.(4)HMF tuned the magnetic properties and the electrocatalytic performance of FePt nanomaterials,and the relationship between the performance transition and the structural evolution of FePt nanomaterials under HMFs was revealed.The magnetic properties of FePt nanomaterials have been measured.The results showed that HMF tuned magnetic properties,such as the low-temperature coercivity,the blocking temperature and the effective anisotropy constants,by changing the sizes and tailoring the shapes of nanoparticles.More interesting,HMF controlled the coercivity,the blocking temperature and the effective anisotropy of FePt nanowires by tuning the lengths.The electrocatalytic activity of FePt concave-cube nanoparticles has been detected.HMF decreased the size of nanoparticles,which resulted the surface area per unit mass and the content of active sites per unit volume(edges and depressions)increased.Thus,the catalytic activity toward the oxygen reduction reaction(ORR)and the methanol oxidation reaction(MOR)were enhanced. |
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