Tuning Fe3O4 for sustainable cathodic heterogeneous electro-Fenton catalysis by acetylated chitosan.

Peroxidase-like catalysts are safe and low-cost candidates to tackle the dilemma in constructing sustainable cathodic heterogeneous electro-Fenton (CHEF) catalysts for water purification, but the elusive structure-property relationship of enzyme-like catalysts constitutes a pressing challenge for the advancement of CHEF processes in practically relevant water and wastewater treatment. Herein, we probe the origins of catalytic efficiency in the CHEF process by artificially tailoring the peroxidase-like activity of Fe3O4 through a series of acetylated chitosan-based hydrogels, which serve as ecofriendly alternatives to traditional carbon shells. The optimized acetylated chitosan wrapping Fe3O4 hydrogel on the cathode shows an impressive activity and stability in CHEF process, overcoming the complicated and environmentally unfavored procedures in the electro-Fenton-related processes. Structural characterizations and theoretical calculations reveal that the amide group in chitosan can modulate the intrinsic redox capacity of surficial Fe sites on Fe3O4 toward CHEF catalysis via the neutral hydrogen bond. This work provides a sustainable path and molecule-level insight for the rational design of high-efficiency CHEF catalysts and beyond.

Synthesis of functionalized mesoporous silica nanoparticles for colorimetric and fluorescence sensing of selective metal (Fe3+) ions in aqueous solution.

The fabrication of red fluorescent hybrid mesoporous silica-based nanosensor materials has promised the bioimaging and selective detection of toxic pollutants in aqueous solutions. In this study, we present a hybrid mesoporous silica nanosensor in which the propidium iodide (PI) was used to conveniently integrate into the mesopore walls using bis(trimethoxysilylpropyl silane) precursors. Various characterization techniques including X-ray diffraction (XRD), Fourier-transform infrared (FTIR), N2 adsorption-desorption, zeta potential, particle size analysis, thermogravimetric, and UV-visible analysis were used to analyze the prepared materials. The prepared PI integrated mesoporous silica nanoparticles (PI-MSNs) selective metal ion sensing capabilities were tested with a variety of heavy metal ions (100 mM), including Ni2+, Cd2+, Co2+, Zn2+, Cr3+, Cu2+, Al3+, Mg2+, Hg2+ and Fe3+ ions. Among the investigated metal ions, the prepared PI-MSNs demonstrated selective monitoring of Fe3+ ions with a significant visible colorimetric pink color change into orange and quenching of pink fluorescence in an aqueous suspension. The selective sensing behavior of PI-MSNs might be due to the interaction of Fe3+ ions with the integrated PI functional fluorophore present in the mesopore walls. Therefore, we emphasize that the prepared PI-MSNs could be efficient for selective monitoring of Fe3+ ions in an aqueous solution and in the biological cellular microenvironment.

Exchange Bias Induced by the Spin-Glass-Like State in a Te-Rich FeGeTe van der Waals Ferromagnet.

We have experimentally investigated the mechanism of the exchange bias in 2D van der Waals (vdW) ferromagnets by means of the anomalous Hall effect (AHE) together with the dynamical magnetization property. The temperature dependence of the AC susceptibility with its frequency response indicates a glassy transition of the magnetic property for the Te-rich FeGeTe vdW ferromagnet. We also found that the irreversible temperature dependence in the anomalous Hall voltage follows the de Almeida-Thouless line. Moreover, the freezing temperature of the spin-glass-like phase is found to correlate with the disappearance temperature of the exchange bias. These important signatures suggest that the emergence of magnetic exchange bias in the 2D van der Waals ferromagnets is induced by the presence of the spin-glass-like state in FeGeTe. The unprecedented insights gained from these findings shed light on the underlying principles governing exchange bias in vdW ferromagnets, contributing to the advancement of our understanding.

Dynamic Behavior of Above-Room-Temperature Robust Skyrmions in 2D Van der Waals Magnet.

Magnetic skyrmions are swirl-like spin configurations that present topological properties, which have great potential as information carriers for future high-density and low-energy-consumption devices. The optimization of skyrmion-hosting materials that can be integrated with semiconductor-based circuits is the primary challenge for their industrialization. Two-dimensional van der Waals ferromagnets are emerging materials that have excellent carrier mobility and compatibility with integrated circuits, making them an ideal candidate for spintronic devices. Here, we report the realization of skyrmions at above room temperature in the 2D ferromagnet Fe3GaTe2. The thickness tunability of their skyrmion size and the formation of the skyrmion lattice are revealed. Furthermore, we demonstrate that the skyrmions can be moved by a low-density current at room temperature, together with an apparent skyrmion Hall effect, which is consistent with our quantitative micromagnetic simulation. Our work offers a promising 2D material platform for harnessing magnetic skyrmions in practical device applications.

Thickness- and Field-Dependent Magnetic Domain Evolution in van der Waals Fe3GaTe2.

The discovery of room-temperature ferromagnetism in van der Waals (vdW) materials opens new avenues for exploring low-dimensional magnetism and its applications in spintronics. Recently, the observation of the room-temperature topological Hall effect in the vdW ferromagnet Fe3GaTe2 suggests the possible existence of room-temperature skyrmions, yet skyrmions have not been directly observed. In this study, real-space imaging was employed to investigate the domain evolution of the labyrinth and skyrmion structure. First, Néel-type skyrmions can be created at room temperature. In addition, the influence of flake thickness and external magnetic field (during field cooling) on both labyrinth domains and the skyrmion lattice is unveiled. Due to the competition between magnetic anisotropy and dipole interactions, the specimen thickness significantly influences the density of skyrmions. These findings demonstrate that Fe3GaTe2 can host room-temperature skyrmions of various sizes, opening up avenues for further study of magnetic topological textures at room temperature.

Controlling Ultrafast Magnetization Dynamics via Coherent Phonon Excitation in a Ferromagnet Monolayer.

Exploring ultrafast magnetization control in 2D magnets via laser pulses is established, yet the interplay between spin dynamics and the lattice remains underexplored. Utilizing real-time time-dependent density functional theory (rt-TDDFT) coupled with Ehrenfest dynamics and nonadiabatic molecular dynamics (NAMD) simulations, we systematically investigate the laser-induced spin-nuclei dynamics with pre-excited A1g and E2g coherent phonons in the 2D ferromagnet Fe3GeTe2 (FGT) monolayer. Selective pre-excitation of coherent phonons under ultrafast laser irradiation significantly alters the local spin moment of FGT, consequently inducing additional spin loss attributed to the nuclear motion-induced asymmetric interatomic charge transfer. Excited spin-resolved charge undergoes a bidirectional spin-flip between spin-down and spin-up states, characterized by a subtle change in the spin moment within approximately 100 fs, followed by unidirectional spin-flip, which will further contribute to the spin moment loss of FGT within tens of picoseconds. Our results shed light on the coupling of coherent phonons with magnetization dynamics in 2D limit.

Enhancing bone regeneration: Unleashing the potential of magnetic nanoparticles in a microtissue model.

Bone tissue engineering addresses the limitations of autologous resources and the risk of allograft disease transmission in bone diseases. In this regard, engineered three-dimensional (3D) models emerge as biomimetic alternatives to natural tissues, replicating intracellular communication. Moreover, the unique properties of super-paramagnetic iron oxide nanoparticles (SPIONs) were shown to promote bone regeneration via enhanced osteogenesis and angiogenesis in bone models. This study aimed to investigate the effects of SPION on both osteogenesis and angiogenesis and characterized a co-culture of Human umbilical vein endothelial cells (HUVEC) and MG-63 cells as a model of bone microtissue. HUVECs: MG-63s with a ratio of 4:1 demonstrated the best results among other cell ratios, and 50 µg/mL of SPION was the optimum concentration for maximum survival, cell migration and mineralization. In addition, the data from gene expression illustrated that the expression of osteogenesis-related genes, including osteopontin, osteocalcin, alkaline phosphatase, and collagen-I, as well as the expression of the angiogenesis-related marker, CD-31, and the tube formation, is significantly elevated when the 50 µg/mL concentration of SPION is applied to the microtissue samples. SPION application in a designed 3D bone microtissue model involving a co-culture of osteoblast and endothelial cells resulted in increased expression of specific markers related to angiogenesis and osteogenesis. This includes the design of a novel biomimetic model to boost blood compatibility and biocompatibility of primary materials while promoting osteogenic activity in microtissue bone models. Moreover, this can improve interaction with surrounding tissues and broaden the knowledge to promote superior-performance implants, preventing device failure.

UV Light-Mediated Hydrolytic Reaction to Develop Magnetic Hydrogel Actuators with Spatially Distributed Ferriferous Oxide Microparticles.

Magnetic hydrogel actuators are developed by incorporating magnetic fillers into the hydrogel matrix. Regulating the distribution of these fillers is key to the exhibited functionalities but is still challenging. Here a facile way to spatially synthesize ferrosoferric oxide (Fe3O4) microparticles in situ in a thermal-responsive hydrogel is reported. This method involves the photo-reduction of Fe3+ ions coordinated with carboxylate groups in polymer chains, and the hydrolytic reaction of the reduced Fe2+ ions with residual Fe3+ ions. By controlling the irradiation time and position, the concentration of Fe3O4 microparticles can be spatially controlled, and the resulting Fe3O4 pattern enables the hydrogel to exhibit complex locomotion driven by magnet, temperature, and NIR light. This method is convenient and extendable to other hydrogel systems to realize more complicated magneto-responsive functionalities.

On-Demand 3D Spatial Distribution of Magnetic Permeability Based on Fe3 O4 Nanoparticle Liquid Toward Micro-Cavity Detectors.

The change of 3D spatial distribution of magnetic permeability can lead to the generation of introduced electrical signals. However, present studies can only achieve rough regulation by simple shape deformation of magnetic elastomers such as compression, bending, or stretching. Accurate control of the 3D spatial distribution of magnetic permeability is still an open question. In this study, an on-demand 3D spatial distribution of magnetic permeability by controlled flowing of Fe3 O4 nanoparticle liquid (FNL) is demonstrated. The flowing routes of FNL are tuned by a 3D-printed cage with pre-designed hollow structure, thus changing the 3D spatial distribution of magnetic permeability. Then, eight symmetrically distributed coils under cage are used to receive characteristic induction voltage signals. Maxwell numerical simulation reveals the working mechanism of signal generation. Notably, those eight coils can detect FNL flowing status in eight directions, allowing recognition of up to 255 different FNL flowing combinations. By introducing machine learning, the micro-cavity detector based on FNL can distinguish nine kinds of micro-cavity structures with an accuracy of 98.77%. This work provides a new strategy for the adjustment of the 3D spatial distribution of the magnetic permeability and expands the application of FNL in the field of space exploration.

Ultra-Low Loading of Ultra-Small Fe3 O4 Nanoparticles on Nonmodified CNTs to Improve Green EMI Shielding Capability of Rubber Composites.

From a material design perspective, the incorporation of Fe3 O4 @carbon nanotube (Fe3 O4 @CNT) hybrids is an effective approach for reconciling the contradictions of high shielding and low reflection coefficients, enabling the fabrication of green shielding materials and reducing the secondary electromagnetic wave pollution. However, the installation of Fe3 O4 nanoparticles on nonmodified and nondestructive CNT walls remains a formidable challenge. Herein, a novel strategy for fabricating the above-mentioned Fe3 O4 @CNTs and subsequently assembling segregated Fe3 O4 @CNT networks in natural rubber (NR) matrices is proposed. The advanced and unique structure, magnetism, and lossless conductivity endow the as-obtained Fe3 O4 @CNT/NR with a shielding effectiveness (SE) of 63.8 dB and a low reflection coefficient of 0.24, which indicates a prominent green-shielding capability that surpasses those of previously reported green-shielding materials. Moreover, the specific SE reaches 531 dB cm-1 , exceeding that of those of previously reported carbon/polymer composites. Meanwhile, the outstanding conductivity enables the composite to reach a saturation temperature of ≈95 °C at a driving voltage of 1.5 V with long-term stability. Therefore, the as-fabricated Fe3 O4 @CNT/rubber composites represent an important development in green-shielding materials that are applied in cold environment.

Highly Efficient Spin Injection and Readout Across Van Der Waals Interface.

Spin injection, transport, and detection across the interface between a ferromagnet and a spin-carrying channel are crucial for energy-efficient spin logic devices. However, interfacial conductance mismatch, spin dephasing, and inefficient spin-to-charge conversion significantly reduce the efficiency of these processes. In this study, it is demonstrated that an all van der Waals heterostructure consisting of a ferromagnet (Fe3GeTe2) and Weyl semimetal enables a large spin readout efficiency. Specifically, a nonlocal spin readout signal of 150 mΩ and a local spin readout signal of 7.8 Ω is achieved, which reach the signal level useful for practical spintronic devices. The remarkable spin readout signal is attributed to suppressed spin dephasing channels at the vdW interfaces, long spin diffusion, and efficient charge-spin interconversion in Td-MoTe2. These findings highlight the potential of vdW heterostructures for spin Hall effect-enabled spin detection with high efficiency, opening up new possibilities for spin-orbit logic devices using vdW interfaces.

Magnetic Tunability via Control of Crystallinity and Size in Polycrystalline Iron Oxide Nanoparticles.

Iron oxide nanoparticles (IONPs) are widely used for biomedical applications due to their unique magnetic properties and biocompatibility. However, the controlled synthesis of IONPs with tunable particle sizes and crystallite/grain sizes to achieve desired magnetic functionalities across single-domain and multi-domain size ranges remains an important challenge. Here, a facile synthetic method is used to produce iron oxide nanospheres (IONSs) with controllable size and crystallinity for magnetic tunability. First, highly crystalline Fe3O4 IONSs (crystallite sizes above 24 nm) having an average diameter of 50 to 400 nm are synthesized with enhanced ferrimagnetic properties. The magnetic properties of these highly crystalline IONSs are comparable to those of their nanocube counterparts, which typically possess superior magnetic properties. Second, the crystallite size can be widely tuned from 37 to 10 nm while maintaining the overall particle diameter, thereby allowing precise manipulation from the ferrimagnetic to the superparamagnetic state. In addition, demonstrations of reaction scale-up and the proposed growth mechanism of the IONSs are presented. This study highlights the pivotal role of crystal size in controlling the magnetic properties of IONSs and offers a viable means to produce IONSs with magnetic properties desirable for wider applications in sensors, electronics, energy, environmental remediation, and biomedicine.

A Minimalist Iron Oxide Nanoprobe for the High-Resolution Depiction of Stroke by Susceptibility-Weighted Imaging.

The precise mapping of collateral circulation and ischemic penumbra is crucial for diagnosing and treating acute ischemic stroke (AIS). Unfortunately, there exists a significant shortage of high-sensitivity and high-resolution in vivo imaging techniques to fulfill this requirement. Herein, a contrast enhanced susceptibility-weighted imaging (CE-SWI) using the minimalist dextran-modified Fe3O4 nanoparticles (Fe3O4@Dextran NPs) are introduced for the highly sensitive and high-resolution AIS depiction under 9.4 T for the first time. The Fe3O4@Dextran NPs are synthesized via a simple one-pot coprecipitation method using commercial reagents under room temperature. It shows merits of small size (hydrodynamic size 25.8 nm), good solubility, high transverse relaxivity (r2) of 51.3 mM-1s-1 at 9.4 T, and superior biocompatibility. The Fe3O4@Dextran NPs-enhanced SWI can highlight the cerebral vessels readily with significantly improved contrast and ultrahigh resolution of 0.1 mm under 9.4 T MR scanner, enabling the clear spatial identification of collateral circulation in the middle cerebral artery occlusion (MCAO) rat model. Furthermore, Fe3O4@Dextran NPs-enhanced SWI facilitates the precise depiction of ischemia core, collaterals, and ischemic penumbra post AIS through matching analysis with other multimodal MR sequences. The proposed Fe3O4@Dextran NPs-enhanced SWI offers a high-sensitivity and high-resolution imaging tool for individualized characterization and personally precise theranostics of stroke patients.

An Approach to Apply BDNF Targeting Fe3O4-Based Nanoparticles as Multifunctional Anti-Alzheimer Agents.

To search for novel anti-Alzheimer agents, multifunctional Fe3O4-based nanoparticles (FSSIO) is designed and prepared which contain ferulic acid (FA) and Simvastatin linked to the surface of Fe3O4 particles. In vitro tests confirmed that FSSIO possessed favorable biocompatibility and a pronounced ability to penetrate blood brain barrier. The FA moiety endowed the particles with remarkable antioxidant and anti-inflammatory properties, and effectively protected neuron cells from the toxicity induced by Aß. Moreover, the Simvastatin pharmacophore assists the particles up-regulate the expression level of BDNF and significantly promotes the expression levels of p-TrkB, p-ERK, p-PI3K and Akt, which consequently leads to the neurite outgrowth via regulating PI3K/ATK and TrkB-mediated signaling pathway. More importantly, in the Morris water maze test, FSSIO shows excellent activity to enhance the learning and memory retention of AD model rats.

M2 Macrophage Membrane-Camouflaged Fe3 O4 -Cy7 Nanoparticles with Reduced Immunogenicity for Targeted NIR/MR Imaging of Atherosclerosis.

Atherosclerosis （AS） is the primary reason behind cardiovascular diseases, leading to approximately one-third of global deaths. Developing a novel multi-model probe to detect AS is urgently required. Macrophages are the primary cells from which AS genesis occurs. Utilizing natural macrophage membranes coated on the surface of nanoparticles is an efficient delivery method to target plaque sites. Herein, Fe3 O4 -Cy7 nanoparticles (Fe3 O4 -Cy7 NPs), functionalized using an M2 macrophage membrane and a liposome extruder for Near-infrared fluorescence and Magnetic resonance imaging, are synthesized. These macrophage membrane-coated nanoparticles (Fe3 O4 @M2 NPs) enhance the recognition and uptake using active macrophages. Moreover, they inhibit uptake using inactive macrophages and human coronary artery endothelial cells. The macrophage membrane-coated nanoparticles (Fe3 O4 @M0 NPs, Fe3 O4 @M1 NPs, Fe3 O4 @M2 NPs) can target specific sites depending on the macrophage membrane type and are related to C-C chemofactor receptor type 2 protein content. Moreover, Fe3 O4 @M2 NPs demonstrate excellent biosafety in vivo after injection, showing a significantly higher Fe concentration in the blood than Fe3 O4 -Cy7 NPs. Therefore, Fe3 O4 @M2 NPs effectively retain the physicochemical properties of nanoparticles and depict reduced immunological response in blood circulation. These NPs mainly reveal enhanced targeting imaging capability for atherosclerotic plaque lesions.

Compressively Strained Fe3O4 in Core-Shell Oxygen Reduction Electrocatalyst Boosts Zinc-Air Battery Performance.

Fe3O4 is barely taken into account as an electrocatalyst for oxygen reduction reaction (ORR), an important reaction for metal-air batteries and fuel cells, due to its sluggish catalytic kinetics and poor electron conductivity. Herein, how strain engineering can be employed to regulate the local electronic structure of Fe3O4 for high ORR activity is reported. Compressively strained Fe3O4 shells with 2.0% shortened Fe─O bond are gained on the Fe/Fe4N cores as a result of lattice mismatch at the interface. A downshift of the d-band center occurs for compressed Fe3O4, leading to weakened chemisorption energy of oxygenated intermediates, and lower reaction overpotential. The compressed Fe3O4 exhibits greatly enhanced electrocatalytic ORR activity with a kinetic current density of 27 times higher than that of pristine one at 0.80 V (vs reversible hydrogen electrode), as well as potential application in zinc-air batteries. The findings provide a new strategy for tuning electronic structures and improving the catalytic activity of other metal catalysts.

Highly Efficient Room-Temperature Nonvolatile Magnetic Switching by Current in Fe3GaTe2 Thin Flakes.

Effectively tuning magnetic state by using current is essential for novel spintronic devices. Magnetic van der Waals (vdW) materials have shown superior properties for the applications of magnetic information storage based on the efficient spin torque effect. However, for most of known vdW ferromagnets, the ferromagnetic transition temperatures lower than room temperature strongly impede their applications and the room-temperature vdW spintronic device with low energy consumption is still a long-sought goal. Here, the highly efficient room-temperature nonvolatile magnetic switching is realized by current in a single-material device based on vdW ferromagnet Fe3GaTe2. Moreover, the switching current density and power dissipation are about 300 and 60000 times smaller than conventional spin-orbit-torque devices of magnet/heavy-metal heterostructures. These findings make an important progress on the applications of magnetic vdW materials in the fields of spintronics and magnetic information storage.

Unusual Dzyaloshinskii-Moriya Interaction in Graphene/Fe3GeTe2 Van der Waals Heterostructure.

Dzyaloshinskii-Moriya interaction (DMI) is shown to induce a topologically protected chiral spin texture in magnetic/nonmagnetic heterostructures. In the context of van der Waals spintronic devices, graphene emerges as an excellent candidate material. However, due to its negligible spin-orbit interaction, inducing DMI to stabilize topological spins when coupled to 3d-ferromagnets remains challenging. Here, it is demonstrated that, despite these challenges, a sizeable Rashba-type spin splitting followed by significant DMI is induced in graphene/Fe3GeTe2. This is made possible due to an interfacial electric field driven by charge asymmetry together with the broken inversion symmetry of the heterostructure. These findings reveal that the enhanced DMI energy parameter, resulting from a large effective electron mass in Fe3GeTe2, remarkably contributes to stabilizing non-collinear spins below the Curie temperature, overcoming the magnetic anisotropy energy. These results are supported by the topological Hall effect, which coexists with the non-trivial breakdown of Fermi liquid behavior, confirming the interplay between spins and non-trivial topology. This work paves the way toward the design and control of interface-driven skyrmion-based devices.

Achieving Fast and Stable Sodium Storage in Na4Fe3(PO4)2(P2O7) via Entropy Engineering.

Na4Fe3(PO4)2(P2O7) (NFPP) has been considered a promising cathode material for sodium-ion batteries (SIBs) owing to its environmental friendliness and economic viability. However, its electrochemical performance is constrained by connatural low electronic conductivity and inadequate sodium ion diffusion. Herein, a high-entropy substitution strategy is employed in NFPP to address these limitations. Ex situ X-ray diffraction analysis reveals a single-phase electrochemical reaction during the sodiation/desodiation processes and the increased configurational entropy in HE-NFPP endows an enhanced structure, which results in a minimal volume variation of only 1.83%. Kinetic analysis and density functional theory calculation further confirm that the orbital hybrid synergy of high-entropy transition metals offers a favorable electronic structure, which efficaciously boosts the charge transfer kinetics and optimizes the sodium ion diffusion channel. Based on this versatile strategy, the as-prepared high-entropy Na4Fe2.5Mn0.1Mg0.1Co0.1Ni0.1Cu0.1(PO4)2(P2O7) (HE-NFPP) cathode can deliver a prominent rate performance of 55 mAh g-1 at 10 A g-1 and an ultra-long cycling lifespan of over 18 000 cycles at 5 A g-1. When paired with a hard carbon (HC) anode, HE-NFPP//HC full cell exhibits a favorable cycling durability of 1000 cycles. This high-entropy engineering offers a feasible route to improve the electrochemical performance of NFPP and provides a blueprint for exploring high-performance SIBs.

A novel ratiometric colorimetric sensor for detecting hypochlorite and ascorbic acid based on cascade reaction.

Hypochlorite and ascorbic acid (AA), play an indispensable role in numerous physiological activities. Herein, a ratiometric colorimetric sensing strategy for the determination of hypochlorite and AA was developed via the catalytic oxidation and reduction of 3,3',5,5'-tetramethylbenzidine (TMB). Interestingly, in the presence of Fe3O4-MOF-5(Fe) and hypochlorite, TMB complexes in acidic environments were oxidized to blue oxidized TMB and further diazotized to produce yellow-green diazotized TMB, resulting in the hypochlorite concentration-dependent ratiometric variation for the absorbance at 652 and 450 nm (A450/A652). Moreover, the diazotized TMB was restored to colorless TMB due to the reducibility of AA, and the detection limit of hypochlorite and AA were 0.027 and 0.677 µM, respectively. The ratiometric colorimetric sensing platform offered higher sensitivity and better selectivity because of the specific hypochlorite-induced reaction and the excellent peroxidase-like activity of Fe3O4-MOF-5(Fe). The proposed novel strategy provided the guidance to develop sensors for successive detection of hypochlorite and AA in complicated samples.