Fe3O4 Nanoparticles Embedded in Uniform Mesoporous Carbon Spheres for Superior High‐Rate Battery Applications

Robust composite structures consisting of Fe₃O₄ nanoparticles (～5 nm) embedded in mesoporous carbon spheres with an average size of about 70 nm (IONP@mC) are synthesized by a facile two‐step method: uniform Fe₃O₄ nanoparticles are first synthesized followed by a post‐synthetic low‐temperature hydrothermal step to encapsulate them in mesoporous carbon spheres. Instead of graphene which has been extensively reported for use in high‐rate battery applications as a carbonaceous material combined with metal oxides mesoporous carbon is chosen to enhance the overall performances. The interconnecting pores facilitate the penetration of electrolyte leading to direct contact between electrochemically active Fe₃O₄ and lithium ion‐carrying electrolyte greatly facilitating lithium ion transportation. The interconnecting carbon framework provides continuous 3D electron transportation routes. The anodes fabricated from IONP@mC are cycled under high current densities ranging from 500 to 10 000 mA g^?1. A high reversible capacity of 271 mAh g^?1 is reached at 10 000 mAh g^?1 demonstrating its superior high rate performance.     

Modular Layer‐by‐Layer Assembly of Polyelectrolytes,Nanoparticles, and Molecular Catalysts into Solar‐to‐Chemical Energy Conversion Devices

The design and fabrication of solar‐to‐chemical energy conversion devices are enabled through interweaving multiple components with various morphologies and unique functions using a versatile layer‐by‐layer assembly method. Cationic and anionic polyelectrolytes are used as an electrostatic adhesive to assemble the following functional materials: plasmonic Ag nanoparticles for improved light harvesting, upconversion nanoparticles for utilization of near‐infrared light, and polyoxometalate water oxidation catalysts for enhanced catalytic activity. Polyelectrolytes also have an additional function of passivating the surface recombination centers of the underlying photoelectrode. These functional components are precisely assembled on a model photoanode (e.g., Fe₂O₃ and BiVO₄) in a desired order and various combinations without degradation of their intrinsic properties. As a result, the performance of water oxidation photoanodes is synergistically enhanced. This study can enable the design and fabrication of novel solar‐to‐chemical energy conversion devices.     

Magnetic Hyperthermia–Synergistic H2O2 Self‐Sufficient Catalytic Suppression of Osteosarcoma with Enhanced Bone‐Regeneration Bioactivity by 3D‐Printing Composite Scaffolds

Chemotherapy resistance and bone defects caused by surgical excision of osteosarcoma have been formidable challenges for clinical treatment. Although recently developed nanocatalysts based on Fenton‐like reactions for catalytic therapy demonstrate high potential to eliminate chemotherapeutic‐insensitive tumors, insufficient concentration of intrinsic hydrogen peroxide (H₂O₂) and low intratumoral penetrability hinder their applications and therapeutic efficiency. The synchronous enriching intratumor H₂O₂ amount or nanoagents and promoting osteogenesis are intriguing strategies to solve the dilemma in osteosarcoma therapy. Herein, a multifunctional “all‐in‐one” biomaterial platform is constructed by co‐loading calcium peroxide (CaO₂) and iron oxide (Fe₃O₄) nanoparticles into a three‐dimensional (3D) printing akermanite scaffold (AKT‐Fe₃O₄‐CaO₂). The loaded CaO₂ nanoparticles act as H₂O₂ sources to achieve H₂O₂ self‐sufficient nanocatalytic osteosarcoma therapy as catalyzed by coloaded Fe₃O₄ nanoagents, as well as provide calcium ion (Ca²⁺) pools to enhance bone regeneration. The synergistic osteosarcoma‐therapeutic effect is achieved from both magnetic hyperthermia as‐enabled by Fe₃O₄ nanoparticles under alternative magnetic fields and hyperthermia‐enhanced Fenton‐like nanocatalytic reaction for producing highly toxic hydroxyl radicals. Importantly, the constructed 3D AKT‐Fe₃O₄‐CaO₂ composite scaffolds are featured with favorable bone‐regeneration activity, providing a worthy base and positive enlightenment for future osteosarcoma treatment with bone defects by the multifunctional biomaterial platforms.     

Continuous Aspect‐Ratio Tuning and Fine Shape Control of Monodisperse α‐Fe2O3 Nanocrystals by a Programmed Microwave–Hydrothermal Method

A rapid and economical route based on an efficient microwave–hydrothermal process has been developed to synthesize monodisperse α‐Fe₂O₃ nanocrystals with continuous aspect‐ratio tuning and fine shape control, which takes advantage of microwave irradiation and hydrothermal effects. This method easily programs the experimental conditions (e.g., temperature and time) and significantly shortens the synthesis time to minutes. It allows the creation of numerous recipes for optimizing and scaling up production. The effects of experimental conditions including reaction temperature and reactant concentration on the morphology of α‐Fe₂O₃ have been investigated systematically. Results reveal that the initial molar ratio of Fe³⁺ to PO plays a crucial role in the final morphology of the α‐Fe₂O₃ products. Several morphologies, which include ellipsoids/spindles with aspect ratios that range from 1.1 to 6.3, nanosheets, nanorings, and spheres can be obtained. The as‐formed α‐Fe₂O₃ exhibits shape‐dependent infrared optical properties. The growth process of colloidal α‐Fe₂O₃ crystals in the presence of phosphate ions is discussed. The products have been characterized by using X‐ray diffraction, scanning electron microscopy, transmission electron microscopy, and infrared spectroscopy. This work presents an efficient and cost‐effective approach that is potentially competitive for scaling‐up industrial production. The as‐formed α‐Fe₂O₃ crystals with controllable morphologies not only provide flexible building blocks for advanced functional devices, but are also ideal candidates for studying their nanoarchitecture‐dependent performance in optical, catalytic, and magnetic applications.     

Adsorbing and Activating N2 on Heterogeneous Au–Fe3O4 Nanoparticles for N2 Fixation

Electrochemical nitrogen reduction reaction (NRR) is a promising approach to convert earth‐adundant N₂ into highly value‐added NH₃. Herein, it is demonstrated that the heterogeneous Au–Fe₃O₄ nanoparticles (NPs) can be adopted as highly efficient catalysts for NRR. Due to the synergistic effect of the strong N₂ fixation ability of Fe₃O₄ and the charge transfer capability of Au, the Au–Fe₃O₄ NPs show excellent performance with a high yield (NH₃: 21.42 µg mg_cat^?1 h^?1) and a favorable faradaic efficiency (NH₃: 10.54%) at ?0.2 V (vs reversible hydrogen electrode), both of which are much better than those of the Au NPs, Fe₃O₄ NPs, as well as core@shell Au@Fe₃O₄ NPs. It also exhibits good stability with largely maintained performance after six cycles. The N₂ temperature‐programmed desorption, surface valance band spectra, and X‐ray photoelectron spectroscopy collectively confirm that Au–Fe₃O₄ NPs have a strong adsorption capacity for the reaction species and suitable surface structure for electronic transfer. The theoretical calculations reveal that Fe provides the active site to fix N₂ into *N₂H while introducing Au optimizes the adsorption of NRR intermediates, making the NRR pathway on Au–Fe₃O₄ along an energetic‐favorable process and enhancing the NRR.     

Surface State Mediated NIR Two‐Photon Fluorescence of Iron Oxides for Nonlinear Optical Microscopy

The development of fluorescent iron oxide nanomaterials is highly desired for multimodal molecular imaging. Instead of incorporating fluorescent dyes on the surface of iron oxides, a ligand‐assisted synthesis approach is developed to allow near‐infrared (NIR) fluorescence in Fe₃O₄ nanostructures. Using a trimesic acid (TMA)/citrate‐mediated synthesis, fabricated Fe₃O₄ nanostructures can generate a NIR two‐photon florescence (TPF) peak around 700 nm under the excitation by a 1230‐nm femtosecond laser. By tailoring the absorption of Fe₃O₄ nanostructures toward NIR band, the NIR‐TPF efficiency can be greatly increased. Through internal etching, surface peeling, and ligand replacement, spectroscopic results validated that such resonantly enhanced NIR‐TPF is mediated by surface states with strong NIR‐IR absorption. This TPF signal evolution can be generalized to other iron oxide nanomaterials like magnetite nanoparticles and α‐Fe₂O₃ nanoplates. Using the developed fluorescent Fe₃O₄ nanostructures, it is demonstrated that their TPF and third harmonic generation (THG) contrast in the nonlinear optical microscopy of live cells. It is anticipated that the synthesized NIR photofunctional Fe₃O₄ will serve as a versatile platform for dual‐modality magnetic resonance imaging (MRI) as well as a magnet‐guided theranostic agent.     

Assembly of Au Plasmonic Photothermal Agent and Iron Oxide Nanoparticles on Ultrathin Black Phosphorus for Targeted Photothermal and Photodynamic Cancer Therapy

Photodynamic therapy (PDT), as a minimally invasive and high‐efficiency anticancer approach, has received extensive research attention recently. Despite plenty of effort devoted to exploring various types of photodynamic agents with strong near‐infrared (NIR) absorbance for PDT and many encouraging progresses achieved in the area, effective and safe photodynamic photosensitizers with good biodegradability and biocompatibility are still highly expected. In this work, a novel nanocomposite has been developed by assembly of iron oxide (Fe₃O₄) nanoparticles (NPs) and Au nanoparticles on black phosphorus sheets (BPs@Au@Fe₃O₄), which shows a broad light absorption band and a photodegradable character. In vitro and in vivo assay indicates that BPs@Au@Fe₃O₄ nanoparticles are highly biocompatible and exhibit excellent tumor inhibition efficacy owing to a synergistic photothermal and photodynamic therapy mediated by a low‐power NIR laser. Importantly, BPs@Au@Fe₃O₄ can anticipatorily suppress tumor growth by visualized synergistic therapy with the help of magnetic resonance imaging (MRI). This work presents the first combination application of the photodynamic and photothermal effect deriving from black phosphorus nanosheets and plasmonic photothermal effect from Au nanoparticles together with MRI from Fe₃O₄ NPs, which may open the new utilization of black phosphorus nanosheets in biomedicine, optoelectronic devices, and photocatalysis.     

Lithium Ion Breathable Electrodes with 3D Hierarchical Architecture for Ultrastable and High‐Capacity Lithium Storage

Transition‐metal oxides show genuine potential in replacing state‐of‐the‐art carbonaceous anode materials in lithium‐ or sodium‐ion batteries because of their much higher theoretical capacity. However, they usually undergo massive volume change, which leads to numerous problems in both material and electrode levels, such as material pulverization, instable solid‐electrolyte interphase, and electrode failure. Here, it is demonstrated that lithium‐ion breathable hybrid electrodes with 3D architecture tackle all these problems, using a typical conversion‐type transition‐metal oxide, Fe₃O₄, of which nanoparticles are anchored onto 3D current collectors of Ni nanotube arrays (NTAs) and encapsulated by δ‐MnO₂ layers (Ni/Fe₃O₄@MnO₂). The δ‐MnO₂ layers reversibly switch lithium insertion/extraction of internal Fe₃O₄ nanoparticles and protect them against pulverizing and detaching from NTA current collectors, securing exceptional integrity retention and efficient ion/electron transport. The Ni/Fe₃O₄@MnO₂ electrodes exhibit superior cyclability and high‐capacity lithium storage (retaining ≈1450 mAh g^?1, ≈96% of initial value at 1 C rate after 1000 cycles).     

Supramolecular Photonic Elastomers with Brilliant Structural Colors and Broad‐Spectrum Responsiveness

Photonic elastomers (PEs) that can tune their colors through adjusting the lattice spacing of incorporated colloidal particles during mechanical deformation have shown great promise in visualized strain/stress sensors. However, the unsatisfactory structural color and narrow‐spectrum responsiveness limit their broad applications. Herein, carbon‐coated Fe₃O₄ nanoparticles (Fe₃O₄@C NPs) with a high refractive index (RI) and broad light absorption are employed for the construction of PEs with brilliant colors and broad‐spectrum responsiveness by incorporating the Fe₃O₄@C NPs into amino‐terminated poly(dimethylsiloxane) (amino‐PDMS) polymer through supramolecular interactions. The inherent light‐absorbing property, high RI, and supramolecular‐induced short‐range ordered arrangement of Fe₃O₄@C NPs imparts the PEs with brilliant and angle‐independent structural color. By optimizing the content of Fe₃O₄@C NPs in the PEs, broad‐spectrum responsiveness (stopband shifting ≈223 nm) and excellent recovery properties under a large strain can be achieved. The dynamic and reversible interaction endows the PEs with a healable capability. More interestingly, the incorporated Fe₃O₄@C NPs with photothermal capability can effectively absorb light and convert it into heat under light irradiation (solar light or near‐infrared laser), accelerating healing of the damaged PEs. This study provides a new strategy for bioinspired construction of PEs for applications in the fields of sensing, colorful coating, and display.     

“Naked” Magnetically Recyclable Mesoporous Au–γ‐Fe2O3 Nanocrystal Clusters: A Highly Integrated Catalyst System

Naked magnetically recyclable mesoporous Au–γ‐Fe₂O₃ clusters, combining the inherent magnetic properties of γ‐Fe₂O₃ and the high catalytic activity of Au nanoparticles (NPs), are successfully synthesized. Hydrophobic Au–Fe₃O₄ dimers are first self‐assembled to form sub‐micrometer‐sized Au–Fe₃O₄ clusters. The Au–Fe₃O₄ clusters are then coated with silica, calcined at 550 °C, and finally alkali treated to dissolve the silica shell, yielding naked‐Au–γ‐Fe₂O₃ clusters containing Au NPs of size 5–8 nm. The silica protection strategy serves to preserve the mesoporous structure of the clusters, inhibit the phase transformation from γ‐Fe₂O₃ to α‐Fe₂O₃, and prevent cluster aggregation during the synthesis. For the reduction of p‐nitrophenol by NaBH₄, the activity of the naked‐Au–γ‐Fe₂O₃ clusters is ≈22 times higher than that of self‐assembled Au–Fe₃O₄ clusters. Moreover, the naked‐Au–γ‐Fe₂O₃ clusters display vastly superior activity for CO oxidation compared with carbon‐supported Au–γ‐Fe₂O₃ dimers, due to the intimate interfacial contact between Au and γ‐Fe₂O₃ in the clusters. Following reaction, the naked‐Au–γ‐Fe₂O₃ clusters can easily be recovered magnetically and reused in different applications, adding to their versatility. Results suggest that naked‐Au–γ‐Fe₂O₃ clusters are a very promising catalytic platform affording high activity. The strategy developed here can easily be adapted to other metal NP–iron oxide systems.     

Morphological Evolution and Magnetic Property of Rare‐Earth‐Doped Hematite Nanoparticles: Promising Contrast Agents for T1‐Weighted Magnetic Resonance Imaging

A series of uniform rare‐earth‐doped hematite (α‐Fe₂O₃) nanoparticles are synthesized by a facile hydrothermal strategy. In a typical case of gadolinium (Gd)‐doped α‐Fe₂O₃, the morphology and chemical composition can be readily tailored by tuning the initial proportion of Gd³⁺/Fe³⁺ sources. As a result, the products are observed to be stretched into more elongated shapes with an increasing dopant ratio. As a benefit of such an elongated morphological feature and Gd³⁺ ions of larger effective magnetic moment than Fe³⁺, the doped product with the highest ratio of Gd³⁺ at 5.7% shows abnormal ferromagnetic features with a remnant magnetization of 0.605 emu g^?1 and a coercivity value of 430 Oe at 4 K. Density of states calculations also reveal the increase of total magnetic moment induced by Gd³⁺ dopant in α‐Fe₂O₃ hosts, as well as possible change of magnetic arrangement. As‐synthesized Gd‐doped α‐Fe₂O₃ nanoparticles are probed as contrast agents for T1‐weighted magnetic resonance imaging, achieving a remarkable enhancement effect for both in vitro and in vivo tests.     

Dendrimer‐Functionalized Iron Oxide Nanoparticles for Specific Targeting and Imaging of Cancer Cells

We demonstrated a unique approach that combines a layer‐by‐layer (LbL) self‐assembly method with dendrimer chemistry to functionalize Fe₃O₄ nanoparticles (NPs) for specific targeting and imaging of cancer cells. In this approach, positively charged Fe₃O₄ NPs (8.4 nm in diameter) synthesized by controlled co‐precipitation of Fe^II and Fe^III ions were modified with a bilayer composed of polystyrene sulfonate sodium salt and folic acid (FA)‐ and fluorescein isothiocyanate (FI)‐functionalized poly(amidoamine) dendrimers of generation 5 (G5.NH₂‐FI‐FA) through electrostatic LbL assembly, followed by an acetylation reaction to neutralize the remaining surface amine groups of G5 dendrimers. Combined flow cytometry, confocal microscopy, transmission electron microscopy, and magnetic resonance imaging studies show that Fe₃O₄/PSS/G5.NHAc‐FI‐FA NPs can specifically target cancer cells overexpressing FA receptors. The present approach to functionalizing Fe₃O₄ NPs opens a new avenue to fabricating various NPs for numerous biological sensing and therapeutic applications.     

Synthesis of PEOlated Fe3O4@SiO2 Nanoparticles via Bioinspired Silification for Magnetic Resonance Imaging

Inspired by the biosilification process, a highly benign synthesis strategy is successfully developed to synthesize PEOlated Fe₃O₄@SiO₂ nanoparticles (PEOFSN) at room temperature and near‐neutral pH. The success of such a strategy lies in the simultaneous encapsulation of Fe₃O₄ nanocrystals and silica precursors into the core of PEO‐based polymeric micelles. The encapsulation results in the formation of a silica shell being confined to the interface between the core and corona of the Fe₃O₄‐nanocrystal‐loaded polymeric micelles. Consequently, the surface of the Fe₃O₄@SiO₂ nanoparticle is intrinsically covered by a layer of free PEO chains, which enable the PEOFSN to be colloidally stable not only at room temperature, but also upon incubation in the presence of proteins under physiological conditions. In addition, the silica shell formation does not cause any detrimental effects to the encapsulated Fe₃O₄ nanocrystals with respect to their size, morphology, crystallinity, and magnetic properties, as shown by their physicochemical behavior. The PEOFSN are shown to be good candidates for magnetic resonance imaging (MRI) contrast agents as demonstrated by the high r₂/r₁ ratio with long‐term stability under high magnetic field, as well as the lack of cytotoxicity.     

Highly Efficient Photoelectrochemical Water Splitting: Surface Modification of Cobalt‐Phosphate‐Loaded Co3O4/Fe2O3 p–n Heterojunction Nanorod Arrays

Hematite (α‐Fe₂O₃) as a photoanode material for photoelectrochemical (PEC) water splitting suffers from the two problems of poor charge separation and slow water oxidation kinetics. The construction of p–n junction nanostructures by coupling of highly stable Co₃O₄ in aqueous alkaline environment to Fe₂O₃ nanorod arrays with delicate energy band positions may be a challenging strategy for efficient PEC water oxidation. It is demonstrated that the designed p‐Co₃O₄/n‐Fe₂O₃ junction exhibits superior photocurrent density, fast water oxidation kinetics, and remarkable charge injection and bulk separation efficiency (η_inj and η_sep), attributing to the high catalytic behavior of Co₃O₄ for the oxygen evolution reaction as well as the induced interfacial electric field that facilitates separation and transportation of charge carriers. In addition, a cocatalyst of cobalt phosphate (Co‐Pi) is introduced, which brings the PEC performance to a high level. The resultant Co‐Pi/Co₃O₄/Ti:Fe₂O₃ photoanode shows a photocurrent density of 2.7 mA cm^?2 at 1.23 V_RHE (V vs reversible hydrogen electrode), 125% higher than that of the Ti:Fe₂O₃ photoanode. The optimized η_inj and η_sep of 91.6 and 23.0% at 1.23 V_RHE are achieved on Co‐Pi/Co₃O₄/Ti:Fe₂O₃, respectively, corresponding to the 70 and 43% improvements compared with those of Ti:Fe₂O₃. Furthermore, Co‐Pi/Co₃O₄/Ti:Fe₂O₃ shows a low onset potential of 0.64 V_RHE and long‐time PEC stability.     

Magnetic Molecularly Imprinted Polymer Nanocomposites via Surface‐Initiated RAFT Polymerization

A general protocol to synthesize superparamagnetic molecularly imprinted polymer particles, using a RAFT‐mediated approach, is described. S‐ propranolol‐imprinted composites were obtained by functionalizing commercially available amino‐modified Fe₃O₄ nanoparticles with a trithiocarbonate agent and subsequently by polymerizing thin molecularly imprinted layers. Different parameters were optimized and their effect on both nanomorphology and imprinting behaviour was studied. Optimum conditions allowed the synthesis of 40 nm composite particles with a 7 nm MIP shell, exhibiting superparamagnetic properties and specific molecular recognition of S‐ propranolol. The possibility of fine‐tuning the surface properties of the particles is demonstrated by using the “living” nature of active RAFT fragments present on the surface of the composites to further functionalize the particles with ethylene glycol methacrylate phosphate polymer brushes.     

Rattle‐Type Fe3O4@CuS Developed to Conduct Magnetically Guided Photoinduced Hyperthermia at First and Second NIR Biological Windows

A therapeutic carrier in the second near‐infrared (NIR) window is created that features magnetic target, magnetic resonance imaging (MRI) diagnosis, and photothermal therapy functions through the manipulation of a magnet and NIR laser. A covellite‐based CuS in the form of rattle‐type Fe₃O₄@CuS nanoparticles is developed to conduct photoinduced hyperthermia at 808 and 1064 nm of the first and second NIR windows, respectively. The Fe₃O₄@CuS nanoparticles exhibit broad NIR absorption from 700 to 1300 nm. The in vitro photothermal results show that the laser intensity obtained using 808 nm irradiation required a twofold increase in its magnitude to achieve the same damage in cells as that obtained using 1064 nm irradiation. Because of the favorable magnetic property of Fe₃O₄, magnetically guided photothermal tumor ablation is performed for assessing both laser exposures. According to the results under the fixed laser intensity and irradiation spot, exposure to 1064 nm completely removed tumors showing no signs of relapse. On the other hand, 808 nm irradiation leads to effective inhibition of growth that remained nearly unchanged for up to 30 d, but the tumors are not completely eliminated. In addition, MRI is performed to monitor rattle‐type Fe₃O₄@CuS localization in the tumor following magnetic attraction.     

Phosphotungstic acid supported on magnetic core–shell nanoparticles with high photocatalytic activity

Fe₃O₄@SiO₂@HPW (12-tungstophosphoric acid) nanoparticles have been successfully obtained by a simple solvothermal and impregnation process. The as-obtained products were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), fourier transform infrared spectrum (FT-IR), inductively coupled plasma (ICP) and MPM5-XL-5 superconducting quantum interference device (SQUID). The results revealed that the heteropolyacids were successfully grown on the Fe₃O₄@SiO₂ nanoparticles. The photocatalytic studies suggested that the Fe₃O₄@SiO₂@HPW nanoparticles show excellent photocatalytic efficiency for the degradation of Rhodamine B (RB) under UV light irradiation. More importantly, the obtained nanoparticles (Fe₃O₄@SiO₂@HPW) could be effectively separated for reuse by simply applying an external magnetic field. Furthermore, the synthesized nanoparticles could keep their efficiency till four cycles.     

High‐Content,Well‐Dispersed γ‐Fe2O3 Nanoparticles Encapsulated in Macroporous Silica with Superior Arsenic Removal Performance

Novel composites of iron oxide encapsulated in macroporous silica with excellent arsenic adsorption performance have been successfully developed. Macroporous silica foams with large pore sizes of ≈100 nm and a high pore volume of 1.6 cm³ g^?1 are chosen as the porous matrix. Electron tomography technique confirms that γ‐Fe₂O₃ nanoparticles with an average particle size of ≈6 nm are spatially well‐dispersed and anchored on the pore walls at even a high γ‐Fe₂O₃ content of 34.8 wt%, rather than forming aggregates inside the pores or on the external surface. The open large‐pore structure, high loading amount, and the non‐aggregated nature of γ‐Fe₂O₃ nanoparticles lead to increased adsorption sites and thus high adsorption capacities of both As (V) and As (III) without pre‐treatment (248 and 320 mg g^?1, respectively). Moreover, the composites can reduce the concentration of both As (V) and As (III) from 100 to 2 μg L^?1. It is also demonstrated that the composites can be applied in a household drinking water treatment device, which can continuously treat 20 L of wastewater containing As (V) with the effluent concentration lower than the World Health Organization standard.     

Controlled Synthesis of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/Ag Core–Shell Composite Nanoparticles with High Electrical Conductivity

The presented method provides an easy processing route to synthesize Fe₃O₄/Ag core–shell composite nanoparticles. Their structures were characterized by x-ray diffraction and transmission electron microscopy. The average size of the Fe₃O₄ core and Ag shell was about 32.0 nm and 5.0 nm (or 28.0 nm), respectively. Furthermore, magnetic measurements showed that the composite nanoparticles exhibited typical superparamagnetic behavior, specific saturation magnetization of ca. 24.0 emu/g, and intrinsic coercivity of 106.0 Oe. At the same time, high conductivity (64.7 S/cm) of the composite nanoparticles was also observed. This method provides an opportunity to synthesize other core–shell (Fe₃O₄) nanoparticles in a single step.     

A One‐Pot Route to Faceted FePt‐Fe3O4 Dumbbells: Probing Morphology–Catalytic Activity Effects in O2 Reduction Catalysis

The design and synthesis of faceted nanoparticles with a controlled composition is of enormous importance to modern catalyst engineering. Faceted FePt‐Fe₃O₄ dumbbell nanoparticles are prepared by a simple, one‐pot technique that avoids the need for expensive additives or preformed seeds. The faceted product consists of an FePt octopod and a cubic Fe₃O₄ lobe, of mean diameter 13.6 and 14.9 nm, respectively. The mass normalized activity for electrocatalytic oxygen reduction shows that this new structure types outperforms related catalysts in alkaline media. This work illustrates the power of morphology control and tailoring crystal facet abundance at the nanoparticle surface for enhancing catalytic performance.