| Iron nitride materials have attracted wide attention in the fields of magnetic materials,biomedicine,energy catalysis and military science due to their advantages of structural diversity,metal-like properties and abundant resources.Specially,γ’-Fe4 N has the advantages of high saturation magnetization comparable to Fe,high Curie temperature,special crystal structure similar to perovskite,high wear resistance and chemical stability,etc.It is not only an excellent soft magnetic material,but also has great application potential in the fields of electrochemical catalytic,environment purification,etc.This paper was devoted to develop the efficient nitrogen sources to replace ammonia gas,and prepared pure γ′-Fe4 N with high saturation magnetization through a simple,economic and eco-friendly method.The effect of transition metal doping,morphology control,composite on the magnetic properties of γ′-Fe4 N was studied,and the potential application of this materials in the field of electrocatalytic hydrogen production was further explored.The details of this paper are as follows:1.The α-Fe2O3 precursor was prepared by solvothermal method,and the pure phase γ′-Fe4 N was successfully synthesized by high temperature nitridation treatment with ethylenediamine as nitrogen source under the protection of N2.This method overcomes the disadvantages of traditional ammonia nitriding low efficiency,and complex tail gas treatment.Ethylenediamine can not only act as an efficient nitrogen source,but also decompose carbon source.A small amount of amorphous carbon was wrapped on the surface of the material to inhibit air oxidation.The synthesis conditions and magnetic properties of γ’-Fe4 N and related by-products were analyzed in detail.The pure γ’-Fe4 N has excellent soft magnetic properties,and its saturation magnetization can reach 163 emu g-1,which is better than other θ-Fe3 C ε-Fe3 N and iron oxide soft magnetic materials.This work provides a simple,eco-friendly and low-cost method for the synthesis of iron nitride with excellent magnetic properties.2.The transition metal Ni,Mn,Co doped(Fex M1-x)4N(M=Ni,Mn,Co)magnetic nanomaterials were prepared respectively.The optimum doping concentration range of different doping atoms was confirmed.The change regular of structural stability,morphology and chemical composition of materials with different doping atoms was explored.The influence of transition metal doping on the magnetic properties ofγ′-Fe4 N was further investigated,and the reasons for the differences in magnetic properties were analyzed based on the trend of magnetic properties changing with different atomic doping concentrations.In this work,the magnetic properties ofγ′-Fe4 N materials were regulated by transition metal doping.3.Two kinds of magnetic γ′-Fe4 N with different morphologies(cuboidal and rodlike)were obtained by simple solvent-regulated combined with ethylenediamine-assisted hot nitridization,using the multilayer nanosheet self-assembly structure of Fe C2O4·2H2O precursor.The multilayer structure of the Fe C2O4·2H2O precursor is beneficial to the efficient penetration of nitrogen sources,improves the nitrization efficiency and reduces the nucleation temperature.The possible mechanism of reaction was proposed and the magnetic properties of samples with different morphologies were compared.It is of great significance to optimize the magnetic properties of iron nitride by adjusting the structure and morphology directly.4.Hard magnetic Co2 C and soft magnetic Fe4 N composites were phosphating,and the magnetic exchange-coupling effect of P-modified Fe4N/Co-based magnetic composites(P-Fe4N/Co2C)was investigated.The composites have the advantages of high saturation magnetization of soft magnetic materials and high coercivity of hard magnetic materials.The exchange-coupling effect generated at the interface as the ratio of soft and hard magnetic phases is 1:4,and the coercivity increased to 1007.8Oe.This provides a route for optimizing the overall magnetic properties of materials through the exchange-coupling effect between soft and hard magnetic phase.5.The application potential of pure γ′-Fe4 N,transition metal-doped(Fex M1-x)4N(M=Ni,Mn,Co),γ′-Fe4 N with different morphologies,P-modified Fe4N/Co-based magnetic composites as electrocatalysts for OER in alkaline solution was further explored.The positive effects of modification methods such as morphology regulation,composite and doping on OER electrocatalytic performance were investigated.γ′-Fe4 N and its modified-materials showed a low overpotential and Tafel slope,well durability in the process of water-splitting hydrogen production,which provided a promising direction for the development of efficient non-noble metal based electrocatalysts. |
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