χ-Fe_5C_2：结构，合成与催化性质调控

铁碳化物,特别是χ-Fe_5C_2,因在多个不同领域的应用长期以来受到研究者的密切关注。事实上,χ-Fe_5C_2已经被认定为铁基费托合成催化剂的活性相。除了作为催化剂外,χ-Fe_5C_2在电化学、磁成像和治疗等方面也有应用价值。自发现以来,人们对χ-Fe_5C_2的结构、稳定性、催化性能等物理化学性质开展了研究。χ-Fe_5C_2的C2/c结构在上世纪60年代初次得到解析,但是受限于样品中常常混合其他氧化铁和碳化铁,在结构方面还存在争议。研究者仍致力于结合先进表征技术和理论方法,利用高纯度的样品来建立更加准确的模型。作为一种亚稳态结构,传统合成方法很难制备高纯度的χ-Fe_5C_2。经过对合成方法的不断探索,物相单一和尺寸形貌可控的合成已经实现。多种铁和碳的前驱体可以用来合成χ-Fe_5C_2,而固-固、固-气和固-液相的碳化过程均能够用来制备不同粒度和形貌的χ-Fe_5C_2。合成方法方面的成果来了对χ-Fe_5C_2物相形成机理的新认识。利用原位表征方法,研究者已经揭示了气固相和液固相制备过程中物相形成的一些细节。无定形的Fe-C复合物的形成与晶化有可能是关键步骤。在新的制备方法基础上,出现了多种调控χ-Fe_5C_2催化活性的新手段。低钴含量的有钴纳米粒子和χ-Fe_5C_2组成的复合体具有非常高的低温费托合成活性。通过第二组分的修饰后可以使χ-Fe_5C_2突破传统的费托合成反应的局限,成为制备低碳烯烃、长链α烯烃、芳烃和含氧化物的新型催化剂。在这篇综述中,我们将回顾自上世纪中期以来对χ-Fe_5C_2物相的研究成果,聚焦于对结构解析,制备方法,生成机制以及在催化性能调控等方面的进展。我们总结了一系列用于制备χ-Fe_5C_2的方法以及控制催化性质的路径。合成方法的突破是更好认识χ-Fe_5C_2物理化学的关键。     

微乳液反应法制备α-Fe2O3超细粒子的研究

铁氧化物胶体微粒的制备具有重要的意义，因为这些氧化物不仅具有理论研究价值，而且在催化、防腐、颜料以及磁记录材料等研究领域都有广泛的应用．Matijevic’和Schemer山最初用三价铁盐的升温强迫水解法制备出多种形状的。－Fe。03和个FeOOH均匀胶体微粒．其后，我们和张玉亭等在无防尘设备的简化实验条件下，按照修改后的实验手续也成功地获得了均匀球状。一饱0。、驷0。等胶体粒子K司，并对制备条件作了进一步研究则．但这些方法所能得到的最小粒子直径约为50urn．考虑到微乳液体系具有分散相液滴极其微小而且又很均匀的特点，本文…     

Three-and two-dimensional calculations for the interface anisotropy dependence of magnetic properties of exchange-spring Nd2Fe(14)B/α-Fe multilayers with out-of-plane easy axes

Hysteresis loops,energy products and magnetic moment distributions of perpendicularly oriented Nd2Fe(14)B/α-Fe exchange-spring multilayers are studied systematically based on both three-dimensional(3D)and one-dimensional(1D)micromagnetic methods,focused on the influence of the interface anisotropy.The calculated results are carefully compared with each other.The interface anisotropy effect is very palpable on the nucleation,pinning and coercive fields when the soft layer is very thin.However,as the soft layer thickness increases,the pinning and coercive fields are almost unchanged with the increment of interface anisotropy though the nucleation field still monotonically rises.Negative interface anisotropy decreases the maximum energy products and increases slightly the angles between the magnetization and applied field.The magnetic moment distributions in the thickness direction at various applied fields demonstrate a progress of three-step magnetic reversal,i.e.,nucleation,evolution and irreversible motion of the domain wall.The above results calculated by two models are in good agreement with each other.Moreover,the in-plane magnetic moment orientations based on two models are different.The 3D calculation shows a progress of generation and disappearance of vortex state,however,the magnetization orientations within the film plane calculated by the 1D model are coherent.Simulation results suggest that negative interface anisotropy is necessarily avoided experimentally.     

磁性半互穿网络智能水凝胶的合成及性质评价

以甲基丙烯酸(MAA)、N-异丙基丙烯酰胺(NIPAAm)、丙烯酰胺(AM)为原料,N,N′-亚甲基双丙烯酰胺(MBA)为交联剂,利用IPN技术并结合磁性的γ-Fe₂O₃增强剂,在水溶液中制备了半互穿网络水凝胶(PMAA/PAM-NIPAAm/γ-Fe₂O₃),研究了水凝胶的溶胀性﹑热稳定性和电磁性。实验表明,水凝胶形成稳定的IPN互穿网络结构且该水凝胶具温度、pH双重敏感性和顺电磁性。所合成的水凝胶在低临界溶解温度31℃以下,具有明显正向温敏性,高于此温度,水凝胶的温度敏感性会逐渐减弱。产品成功克服了NIPAAm类水凝胶的温缩性。     

A Metal-Organic-Framework-Derived g-C3N4/α-Fe2O3 Hybrid for Enhanced Visible-Light-Driven Photocatalytic Hydrogen Evolution

As one of the most efficient systems for photocatalytic hydrogen evolution, the Z-Scheme system, consisting of different semiconductors with a reversible donor–acceptor pair, has attracted great attention. Considering the non-toxicity and low cost of photocatalysts, a series of g-C₃N₄/α-Fe₂O₃ hybrids were rationally constructed based on the Z-Scheme mechanism for the first time, using a metal-organic framework template approach that can fine tune the compositions and properties of the hybrids. An optimized hybrid, g-C₃N₄/α-Fe₂O₃-2, exhibited prominent photocatalytic water splitting performance with a visible light response. Under irradiation of visible light (λ>420 nm), the hybrid shows a high durability and superior hydrogen production rate of 2066.2 μmol g⁻¹ h⁻¹ from water splitting, which is approximately three times greater than that of bulk g-C₃N₄ because of the effective separation of photo-excited charge carriers by two narrow band gap semiconductors, tightly coupled with the Z-Scheme structural feature.     

Synthesis of KIT-5 decorated by Bi2S3-Fe3O4 photocatalyst for degradation of parathion pesticide in aqueous media: Offering a degradation model and optimization using response surface methodology (RSM)

In this research, a novel KIT-5/Bi₂S₃-Fe₃O₄ nanocomposite was prepared. The structure and morphology properties of the nanocomposite were well characterized by XRD, FESEM-EDS-mapping, TEM, and N₂ adsorption–desorption. Benefiting from the visible light, the as-prepared KIT-5/Bi₂S₃-Fe₃O₄ nanocomposite exhibit significantly improved photocatalytic performance for the degradation of parathion. The optimum photocatalytic efficiency of KIT-5/Bi₂S₃-Fe₃O₄ nanocomposite was investigated with the central composite design using Design Expert software. The four critical variables affecting parathion degradation such as the concentration of parathion, pH, irradiation time, and amount of KIT-5/Bi₂S₃-Fe₃O₄ nanocatalyst. A polynomial function corresponding to degradation percent was obtained for the experimental data. The results showed that this catalyst has a good performance for the degradation of parathion.     

水热合成法制备纳米α-Fe_2O_3粉体及光催化性能研究

以氯化铁和三乙烯四胺为原料,采用水热合成法制备了纳米α-Fe2O3。对样品进行了XRD、FT-IR、TEM表征分析,并研究了其光催化性能。研究结果表明,随着Fe Cl3与C6H18N4摩尔比的增大,纳米颗粒先增大后减小,当n(Fe Cl3)∶n(C6H18N4)=1∶1,样品为结晶度较好的50~80 nm的近方形颗粒,且分散性较好。当n(Fe Cl3)∶n(C6H18N4)=2∶1,样品颗粒最小,光催化性能最好。随着水热反应时间延长,样品颗粒尺寸减小,当水热反应0.5 h时,样品为形貌不规则、界面不清晰、有毛绒状物质附着的60~70 nm的圆形颗粒,有团聚,结晶度较差。当水热反应1 h时,样品为粒径65 nm左右的近方形均匀块状颗粒,且分散性较好,结晶度较高。继续延长水热反应时间,样品形貌变化且颗粒减小,光催化性能逐渐增强。     

α-Fe2O3/石墨烯水凝胶复合材料的自组装制备及电化学性能

采用水热法自组装合成超薄α-Fe₂O₃/还原氧化石墨烯水凝胶（3DGH）复合材料.复合材料的物性表征和电化学测试结果表明,α-Fe₂O₃/3DGH材料呈三维多孔结构,直径约100 nm的α-Fe₂O₃颗粒均匀生长在还原氧化石墨烯片层上;通过调节复合材料中Fe³⁺的负载量,可实现α-Fe₂O₃颗粒的可控生长,粒径为200~30 nm;作为超级电容器的电极材料,α-Fe₂O₃粒径为100 nm左右时,铁负载量为40%的α-Fe₂O₃/3DGH复合材料具有最大的比电容（750.8 F/g,1 A/g）和循环稳定性（在10 A/g电流密度下,充放电5000次后比电容保持率为81.9%）,高于纯α-Fe₂O₃材料的比电容（251.6 F/g,1 A/g）和循环稳定性（充放电5000次后比电容保持率为43.8%）.     

Increase of γ-Fe2O3/CNT composite quantum capacitance by structural design for performance optimization of electrode materials

Performance optimization of electrode materials for lithium-ion batteries is one the most important scientific problems. In this paper, we suggest structural design of γ-Fe₂O₃/CNT composite for increase of its quantum capacitance that is required by modern energy storage devices capable of quick transfer or accumulation of energy and ensuring long-term autonomous operation. For this goal, we investigate the specific quantum capacitance of the γ-Fe₂O₃/CNT composites with a different content of maghemite by quantum chemical methods. The content of maghemite is varied by length of CNTs as well as by number of γ-Fe₂O₃ unit cell the weight ratio equals 13.71%, 20.74%, 26.69%, and 34.30%. It is found that the quantum capacitance grows with increasing maghemite concentration. Calculations show that the value of QC at the Fermi level for γ-Fe₂O₃/CNT is correlated with the theoretical specific capacity of the material. Proposed in this work approach to calculating the quantum capacitance with further analysis of its dependence on voltage can be an effective tool for optimizing the content of the composite with the aim of balancing the Faradaic and non-Faradaic component of its functional activity.     

准立方体α-Fe_2O_3纳米薄膜的紫外和红外光谱研究

采用浸渍提拉法制备了准立方体α-Fe2O3纳米薄膜,利用XRD、AFM、UV-Vis和FT-IR对其表面形貌和谱学性质进行了表征。结果表明,α-Fe2O3单层膜是由粒径约为58nm的粒子排布而成,在568、482和386cm-1处有特征红外吸收峰,在紫外区375nm处存在明显的吸收,为Fe-O间的电子跃迁,其吸光度值与膜层数间的较好线性关系说明在一定的速度下挂膜,可以将氧化铁溶胶中的纳米粒子较好地转移到基片上。