Ziyu Yang

Magnetic Nanomaterials: Chemical Design, Synthesis, and Potential Applications

Magnetic nanomaterials (MNMs) have attracted significant interest in the past few decades because of their unique properties such as superparamagnetism, which results from the influence of thermal energy on a ferromagnetic nanoparticle. In the superparamagnetic size regime, the moments of nanoparticles fluctuate as a result of thermal energy. To understand the fundamental behavior of superparamagnetism and develop relevant potential applications, various preparation routes have been explored to produce MNMs with desired properties and structures. However, some challenges remain for the preparation of well-defined magnetic nanostructures, including exchange-coupled nanomagnets, which are considered as the next generation of advanced magnets. In such a case, effective synthetic methods are required to achieve control over the chemical composition, size, and structure of MNMs. For instance, liquid-phase chemical syntheses, a set of emerging approaches to prepare various magnetic nanostructures, facilitate precise control over the nucleation and specific growth processes of nanomaterials with diverse structures. Among them, the high-temperature organic-phase method is an indispensable one in which the microstructures and physical/chemical properties of MNMs can be tuned by controlling the reaction conditions such as precursor, surfactant, or solvent amounts, reaction temperature or time, reaction atmosphere, etc. In this Account, we present an overview of our progress on the chemical synthesis of various MNMs, including monocomponent nanostructures (e.g., metals, metal alloys, metal oxides/carbides) and multicomponent nanostructures (heterostructures and exchange-coupled nanomagnets). We emphasize the high-temperature organic-phase synthetic method, on which we have been focused over the past decade. Notably, multicomponent nanostructures, obtained by growing or incorporating different functional components together, not only retain the functionalities of each single component but also possess synergic properties that emerge from interfacial coupling, with improved magnetic, optical, or catalytic features. Herein, potential applications of MNMs are covered in three representative areas: biomedicine, catalysis, and environmental purification. Regarding biomedicine, MNMs can detect or target biological entities after being modified with specific biomolecules, and they can be applied to magnetic resonance imaging, imaging-guided drug delivery, and photothermal therapy. Apart from their magnetic features, the catalytic performance of some MNMs resulting from their highly specific chemical components and surface structure will be briefly introduced, highlighting its impact in the methanol oxidation reaction, the oxygen reduction reaction, the oxygen and hydrogen evolution reactions, and the Fischer-Tropsch synthesis. Finally, environmental purification, primarily for water remediation, will be highlighted with two main aspects: the effective capture of bacteria and the removal of adverse ions in wastewater. We hope that this Account will clarify the progress on the controllable preparation of MNMs with specific compositions, sizes, and structures and generate broad interest in the realms of biomedicine and catalysis as well as in environmental issues and other potential applications.

Chemical synthesis, structure and magnetic properties of Co nanorods decorated with Fe 3 O 4 nanoparticles

Magnetic anisotropic nanocomposites have attracted tremendous interests, due to their unexpected properties originating from the interactions of the interfaces except for the intrinsic features. In this work, we develop a facile solution chemistry synthesis method to prepare the one-dimensional (1D) Co-Fe3O4 heterostructures with hard magnetic property. Interestingly, the Fe precursor firstly decompose and nucleate individually, and then grow on the surface of the hexagonal closed-packed (hcp) Co nanorods (NRs) upon prolonging heating time at higher temperature, which is different from the general seed-mediated growth model. The distribution density of Fe3O4 nanoparticles (NPs) on the surface of the Co NRs can be varied with the addition of Fe source, modulating the values of coercivity and saturation magnetization for the Co-Fe3O4 heterostructures. The as-synthesizedCo-Fe3O4 heterostructures maintain the hard magnetic properties with a coercivity value more than 2.5 kOe as well as a saturation magnetization value up to 128.3 emu g−1, indicating the preservation of the anisotropy of the hcp Co NRs.摘要各向异性的磁性异质纳米材料因其各组分之间的相互作用, 可获得不同于单一组分的增强性能、 甚至出现新的功能特性. 本文通过一种简单的高温液相合成方法, 制备了具备硬磁性能的一维Co-Fe3O4异质纳米复合结构. 研究表明, 在此异质结的生长过程中, 铁前驱体是先受热分解并单独形核, 之后, 再通过高温反应在密排六方晶体结构(hcp)Co纳米棒表面进行生长, 有别于常规的晶种-形核生长模式. 另外, Co纳米棒表面负载的Fe3O4纳米颗粒的密度可通过反应过程中铁前驱体的添加量进行控制, 进而对其磁学性能如矫顽力(Hc)和饱和磁化强度(Ms)等进行调控. 通过此过程获得的Co-Fe3O4异质纳米复合材料表现为硬磁性能, Ms值最高可达128.3 emu g−1, Hc值最高可达2.5 kOe, 较好地保持了原始Co纳米棒的磁各向异性.

Galvanic Displacement Synthesis of Monodisperse Janus- and Satellite-Like Plasmonic-Magnetic Ag-Fe@Fe3O4 Heterostructures with Reduced Cytotoxicity

Abstract The unique physicochemical properties of silver nanoparticles offer a large potential for biomedical application, however, the serious biotoxicity restricts their usage. Herein, nanogalvanic couple Ag–Fe@Fe3O4 heterostructures (AFHs) are designed to prevent Ag+ release from the cathodic Ag by sacrificial anodic Fe, which can reduce the cytotoxicity of Ag. AFHs are synthesized with modified galvanic displacement strategy in nonaqueous solution. To eliminate the restriction of lattice mismatch between Fe and Ag, amorphous Fe@Fe3O4 nanoparticles (NPs) are selected as seeds, meanwhile, reductive Fe can reduce Ag precursor directly even at as low as 20 °C without additional reductant. The thickness of the Fe3O4 shell can influence the amorphous properties of AFHs, and a series of Janus‐ and satellite‐like AFHs are synthesized. A “cut‐off thickness” effect is proposed based on the abnormal phenomenon that with the increase of reaction temperature, the diameter of Ag in AFHs decreases. Because of the interphase interaction and the coupling effect of Ag and Fe@Fe3O4, the AFHs exhibit unique optical and magnetic properties. This strategy for synthesis of monodisperse heterostructures can be extended for other metals, such as Au and Cu.