Microwave absorption enhancement of multifunctional composite microspheres with spinel Fe3 O4 Cores and Anatase TiO2 shells

Multifunctional composite microspheres with spinel Fe(3)O(4) cores and anatase TiO(2) shells (Fe(3)O(4)@TiO(2)) are synthesized by combining a solvothermal reaction and calcination process. The size, morphology, microstructure, phase purity, and magnetic properties are characterized by scanning electron microscopy, transmission electron microscopy (TEM), high-resolution TEM, selected-area electron diffraction, electron energy loss spectroscopy, powder X-ray diffraction, and superconducting quantum interference device magnetometry. The results show that the as-synthesized microspheres have a unique morphology, uniform size, good crystallinity, favorable superparamagnetism, and high magnetization. By varying the experimental conditions such as Fe(3)O(4) size and concentration, microspheres with different core sizes and shell thickneses can be readily synthesized. Furthermore, the microwave absorption properties of these microspheres are investigated in terms of complex permittivity and permeability. By integration of the chemical composition and unique structure, the Fe(3)O(4)@TiO(2) microspheres possess lower reflection loss and a wider absorption frequency range than pure Fe(3)O(4). Moreover, the electromagnetic data demonstrate that Fe(3)O(4@TiO(2) microspheres with thicker TiO(2) shells exhibit significantly enhanced microwave absorption properties compared to those with thinner TiO(2) shells, which may result from effective complementarities between dielectric loss and magnetic loss. All the results indicate that these Fe(3)O(4)@TiO(2) microspheres may be attractive candidate materials for microwave absorption applications.     

Fabrication of Novel Hierarchical Structured Fe3O4@LnPO4 (Ln=Eu,Tb, Er) Multifunctional Microspheres for Capturing and Labeling Phosphopeptides

Novel core–shell structured Fe₃O₄@LnPO₄ (Ln=Eu, Tb, Er) multifunctional microspheres with a magnetic Fe₃O₄ core and a LnPO₄ shell covered with spikes are synthesized for the first time through the combination of a homogeneous precipitation approach and an ion‐exchange process. Their potential for selective capture, rapid separation, and easy mass spectrometry (MS) labeling of the phosphopeptides from complex proteolytic digests are evaluated. These affinity microspheres can improve the specificity for capture of the phosphopeptides, realize fast magnetic separation, enhance the MS detection signals, and directly identify phosphopeptides through 80 Da mass loss in the mass spectra. The synthesis strategy could become a general and effective technique for similar core–shell hierarchical structures.     

Functional Fe3O4/TiO2 core/shell magnetic nanoparticles as photokilling agents for pathogenic bacteria

A photokilling approach for pathogenic bacteria is demonstrated using a new type of magnetic nanoprobe as the photokilling agent. In addition to their magnetic property, the nanoprobes have other features including a photocatalytic property and the capacity to target bacteria. The nanoprobes comprise iron oxide/titania (Fe(3)O(4)@TiO(2)) core/shell magnetic nanoparticles. As dopamine molecules can self-assemble onto the surface of the titania substrate, dopamine is used as the linker to immobilize succinic anhydride onto the surfaces of the Fe(3)O(4)@TiO(2) nanoparticles. This is followed by the immobilization of IgG via amide bonding. We demonstrate that the IgG-Fe(3)O(4)@TiO(2) magnetic nanoparticles not only have the capacity to target several pathogenic bacteria, but they also can effectively inhibit the cell growth of the bacteria targeted by the nanoparticles under irradiation of a low-power UV lamp within a short period. Staphylococcus saprophyticus, Streptococcus pyogenes, and antibiotic-resistant bacterial strains, such as multiantibiotic-resistant S. pyogenes and methicillin-resistant Staphylococcus aureus (MRSA), are used to demonstrate the feasibility of this approach.     

Ligand‐Free Fe3O4/CMCS Nanoclusters with Negative Charges for Efficient Structure‐Selective Protein Adsorption

The easy and effective capture of a single protein from a complex mixture is of great significance in proteomics and diagnostics. However, adsorbing nanomaterials are commonly decorated with specific ligands through a complicated and arduous process. Fe₃O₄/carboxymethylated chitosan (Fe₃O₄/CMCS) nanoclusters are developed as a new nonligand modified strategy to selectively capture bovine hemoglogin (BHB) and other structurally similar proteins (i.e., lysozyme (LYZ) and chymotrypsin (CTP)). The ligand‐free Fe₃O₄/CMCS nanoclusters, in addition to their simple and economical two‐step preparation process, possess many merits, including uniform morphology, high negative charges (?27 mV), high saturation magnetization (60 emu g^?1), and high magnetic content (85%). Additionally, the ligand‐free Fe₃O₄/CMCS nanoclusters are found to selectively capture BHB in a model protein mixture even within biological samples. The reason for selective protein capture is further investigated from nanomaterials and protein structure. In terms of nanomaterials, it is found that high negative charges are conducive to selectively adsorb BHB. In consideration of protein structure, interestingly, the ligand‐free magnetic nanoclusters display a structure‐selective protein adsorption capacity to efficiently capture other proteins structurally similar to BHB, such as LYZ and CTP, showing great potential of the ligand‐free strategy in biomedical field.     

Phase Modulation of (1T‐2H)‐MoSe2/TiC‐C Shell/Core Arrays via Nitrogen Doping for Highly Efficient Hydrogen Evolution Reaction

Tailoring molybdenum selenide electrocatalysts with tunable phase and morphology is of great importance for advancement of hydrogen evolution reaction (HER). In this work, phase‐ and morphology‐modulated N‐doped MoSe₂/TiC‐C shell/core arrays through a facile hydrothermal and postannealing treatment strategy are reported. Highly conductive TiC‐C nanorod arrays serve as the backbone for MoSe₂ nanosheets to form high‐quality MoSe₂/TiC‐C shell/core arrays. Impressively, continuous phase modulation of MoSe₂ is realized on the MoSe₂/TiC‐C arrays. Except for the pure 1T‐MoSe₂ and 2H‐MoSe₂, mixed (1T‐2H)‐MoSe₂ nanosheets are achieved in the N‐MoSe₂ by N doping and demonstrated by spherical aberration electron microscope. Plausible mechanism of phase transformation and different doping sites of N atom are proposed via theoretical calculation. The much smaller energy barrier, longer H? Se bond length, and diminished bandgap endow N‐MoSe₂/TiC‐C arrays with substantially superior HER performance compared to 1T and 2H phase counterparts. Impressively, the designed N‐MoSe₂/TiC‐C arrays exhibit a low overpotential of 137 mV at a large current density of 100 mA cm^?2, and a small Tafel slope of 32 mV dec^?1. Our results pave the way to unravel the enhancement mechanism of HER on 2D transition metal dichalcogenides by N doping.     

Conformal Coating of Co/N‐Doped Carbon Layers into Mesoporous Silica for Highly Efficient Catalytic Dehydrogenation–Hydrogenation Tandem Reactions

To maximize the utilizing efficiency of cobalt (Co) and optimize its catalytic activity and stability, engineering of size and interfacial chemical properties, as well as controllable support are of ultimate importance. Here, the concept of coating uniform thin Co/N‐doped carbon layers into the mesopore surfaces of mesoporous silica is proposed for heterogeneous aqueous catalysis. To approach the target, a one‐step solvent‐free melting‐assisted coating process, i.e., heating a mixture of a cobalt salt, an amino acid (AA), and a mesoporous silica, is developed for the synthesis of mesoporous composites with thin Co/N‐doped carbon layers uniformly coated within mesoporous silica, high surface areas (250–630 m² g⁻¹), ordered mesopores (7.0–8.4 nm), and high water dispersibility. The strong silica/AA adhesive interactions and AA cohesive interactions direct the uniform coating process. The metal/N coordinating, carbon anchoring, and mesopore confining lead to the formation of tiny Co nanoclusters. The carbon intercalation and N coordination optimize the interfacial properties of Co for catalysis. The optimized catalyst exhibits excellent catalytic performance for tandem hydrogenation of nitrobenzene and dehydrogenation of NaBH₄ with well‐matched reaction kinetics, 100% conversion and selectivity, high turnover frequencies, up to ≈6.06 mol_nitrobenzene mol_Co⁻¹ min⁻¹, the highest over transition‐metal catalysts, and excellent stability and magnetic separability.     

High-Entropy Doping Boosts Ion/Electronic Transport of Na4Fe3(PO4)2(P2O7)/C Cathode for Superior Performance Sodium-Ion Batteries

Fe-based mixed phosphate cathodes for Na-ion batteries usually possess weak rate capacity and cycle stability challenges resulting from sluggish diffusion kinetics and poor conductivity under the relatively low preparation temperature. Here, the excellent sodium storage capability of this system is obtained by introducing the high-entropy doping to enhance the electronic and ionic conductivity. As designed high-entropy doping Na₄Fe_2.85(Ni,Co,Mn,Cu,Mg)_0.03(PO₄)₂P₂O₇ (NFPP-HE) cathode can release 122 mAh g⁻¹ at 0.1 C, even 85 mAh g⁻¹ at ultrahigh rate of 50 C, and keep a high retention of 82.3% after 1500 cycles at 10 C. Besides, the cathode also exhibits outstanding fast charge capacity in terms of the cyclability and capacity with 105 mAh g⁻¹ at 5 C/1 C, corresponding 94.3% retention after 500 cycles. The combination of in situ X-ray diffraction, density functional theory, conductive-atomic force microscopy, and galvanostatic intermittent titration technique tests reveal that the reversible structure evolution with optimized Na⁺ migration path and energy barrier boost the Na⁺ kinetics and improve the interfacial electronic transfer, thus improving performance.     

Combining X‐Ray Whole Powder Pattern Modeling,Rietveld and Pair Distribution Function Analyses as a Novel Bulk Approach to Study Interfaces in Heteronanostructures: Oxidation Front in FeO/Fe3O4 Core/Shell Nanoparticles as a Case Study

Understanding the microstructure in heterostructured nanoparticles is crucial to harnessing their properties. Although microscopy is ideal for this purpose, it allows for the analysis of only a few nanoparticles. Thus, there is a need for structural methods that take the whole sample into account. Here, a novel bulk‐approach based on the combined analysis of synchrotron X‐ray powder diffraction with whole powder pattern modeling, Rietveld and pair distribution function is presented. The microstructural temporal evolution of FeO/Fe₃O₄ core/shell nanocubes is studied at different time intervals. The results indicate that a two‐phase approach (FeO and Fe₃O₄) is not sufficient to successfully fit the data and two additional interface phases (FeO and Fe₃O₄) are needed to obtain satisfactory fits, i.e., an onion‐type structure. The analysis shows that the Fe₃O₄ phases grow to some extent (≈1 nm) at the expense of the FeO core. Moreover, the FeO core progressively changes its stoichiometry to accommodate more oxygen. The temporal evolution of the parameters indicates that the structure of the FeO/Fe₃O₄ nanocubes is rather stable, although the exact interface structure slightly evolves with time. This approach paves the way for average studies of interfaces in different kinds of heterostructured nanoparticles, particularly in cases where spectroscopic methods have some limitations.     

Magnetic Field-Assisted Interface Embedding Strategy to Construct 2D/3D Composite Structure for Stable Perovskite Solar Cells with Efficiency Over 24%

Perovskite solar cells (PSCs) based on 2D/3D composite structure have shown enormous potential to combine high efficiency of 3D perovskite with high stability of 2D perovskite. However, there are still substantial non-radiative losses produced from trap states at grain boundaries or on the surface of conventional 2D/3D composite structure perovskite film, which limits device performance and stability. In this work, a multifunctional magnetic field-assisted interfacial embedding strategy is developed to construct 2D/3D composite structure. The composite structure not only improves crystallinity and passivates defects of perovskite layer, but also can efficiently promote vertical hole transport and provide lateral barrier effect. Meanwhile, the composite structure also forms a good surface and internal encapsulation of 3D perovskite to inhibit water diffusion. As a result, the multifunctional effect effectively improves open-circuit voltage and fill factor, reaching maximum values of 1.246 V and 81.36%, respectively, and finally achieves power conversion efficiency (PCE) of 24.21%. The unencapsulated devices also demonstrate highly improved long-term stability and humidity stability. Furthermore, an augmented performance of 21.23% is achieved, which is the highest PCE of flexible device based on 2D/3D composite perovskite films coupled with the best mechanical stability due to the 2D/3D alternating structure.