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Composition and structural design play a very influential role in the microwave absorption (MA) manipulation of ferrite/carbon composites. Here, by carefully choosing the dimensionality of the bio-carbon materials, the interfacial geometries and MA properties of ferrite/bio-carbon composites have been controlled effectively. The one dimensional (1D), two dimensional (2D), and three dimensional (3D) biomass-based carbon materials decorated with ZnFe2O4 (ZFO) particles were obtained respectively from carbon fibers (1D), tree leaves (2D), wheat straw (2D), peanut shell (3D) and orange peel (3D) by a simple two-step synthesis method. With increasing the bio-carbon's dimensionality from 1D, 2D to 3D, the ferrite/carbon composite's MA properties are promoted and the minimum reflection loss is enhanced from −9 dB to −45 dB. By changing the ZFO/3D-bio-carbon samples' thickness, a broad absorption range from 4 to 18 GHz can be covered. Moreover, the effective absorption bandwidth for ZFO/3D-bio-carbon can be modified up to 7.1 GHz, which covers the whole Ku band. These observations identified the important roles of the ferrite/carbon interface and dimensionality of carbon materials and provided an effective and low-cost route to design microwave absorption materials based on biomass-industrial waste composites.

Utilization of biomass waste and solid industrial waste, one of the basic solutions of green economy, has become an important topic in both chemical and materials science. Individual bio-carbon, magnetic oxides, and their composites have been used in making microwave absorbers. Here, by utilizing coffee waste bio-carbon and industrial waste MnFe2O4 particles, an efficient microwave absorber has been realized based on their composites. The microwave absorption performance as well as the magnetization of as-synthesized composites can be tuned by adjusting the particle size of MnFe2O4. The minimum reflection loss (RLmini) can be enhanced around 5 times from -7.7 dB to -38.80 dB at 9.8 GHz when mean particle size of MnFe2O4 in the composites is reduced from 9.7 down to 0.9 μm. Meanwhile, a wide effective absorption bandwidth (7.8–11.4 GHz) is achieved in this bio-industrial-waste composite. Such enhancement is explained from viewpoint of appropriate impedance matching as well as the synergetic effect between the bio-carbon and the MnFe2O4. Our work provides a route for the utilization of bio-carbon waste and industrial magnetic waste in the field of microwave absorption.

Developing lightweight and inexpensive absorbents with strong and broadband absorbing performance toward microwave radiation is a challenging but pressing task. Here we report that rice husk-derived silica-hybridized holey carbon fabricated by combining pyrolysis and plasma processing methods is active for the microwave absorbing. The obtained metal-free product is barely prepared from wasted biomass without any additive reagents addition. The results demonstrate at the thickness of 1.5 mm, its reflection loss reaches −43.0 dB at 13.36 GHz and the corresponding absorption bandwidth approaches 3.68 GHz (from 11.44 GHz to 15.12 GHz), over-performing most bare biomass-derived absorbents. The enhanced performance is attributed to the silica blocks existing on surface, which is inherited from the raw rice husk precursor and will construct abundant hybridized contact sites with the derived carbon matrix, thereby providing plenty of interfacial polarizations. Meanwhile, the post plasma treatment can generate rich tiny holes on the carbon matrix, and endow it with high surface areas associated with a great variety of defective sites, and hence regulating the dielectric loss of the final product. It is anticipated that these can represent a feasible addition to the family of wasted biomass-derived sustainable microwave absorbents.

Metal-free graphene-based nanocomposites with small organic molecules interaction are studied as a lightweight, wide bandwidth, and strong absorption microwave absorption material. During hydrothermal process, graphene oxide (GO) precursors are reduced and aggregated into 3D porous network structure. Meanwhile, anthraquinone molecules are intercalated and immobilized on RGO surface through noncovalent π–π stacking. For the obtained RGO@anthraquinone, noncovalent functionalization at interface can modify the electronic states and regulate the electrical conductivity of graphene substrate and its sheet-like structure can be largely maintained. Integrating the intrinsic 3D porous structure, good impedance matching, high conductive loss, and noncovalent interaction, the as-achieved RGO@anthraquinone composites exhibit excellent microwave absorption performance in the X and Ku band. Such as RGO@2-hydroxyanthraquinone (2-HAQ), its optimal absorption toward microwave can reach −54.2 dB at 12.8 GHz with a thickness of 3.0 mm, and its effective absorption bandwidth lower than −10 dB exceeds 7.0 GHz (from 10.96 to 18.0 GHz). When the thickness is controlled between 2.8 and 3.5 mm, the effective absorption bandwidth can cover the whole X and Ku bands (8.0–18.0 GHz). This opens ways to achieve new microwave absorbers with high-performance and provides more opportunities to activate MA behavior on carbon-based metal-free absorbers.

MCo2O4 (M = Mn,Ni) microparticles were synthesised by a simple hydrothermal solvothermal method. The samples were characterised by X-ray diffraction, X-ray energy dispersive spectroscopy and scanni...

In this paper, one-dimensional Fe3O4/C core/shell nanorods (NRs) were successfully prepared through magnetic-field-induced (MFI) assembly approach (0.3 T) and subsequent high-temperature carbonizat...

The monodisperse Ni0.5Zn0.5Fe2O4nanospheres have been synthesized via a simple solvothermal method. The effects of reactant concentration on structural and magnetic properties have been studied. X-ray diffraction analysis results indicate that the lattice constant and crystallite size can be tuned by controlling reactant concentration. The nanosphere size monotonically decreases from 238 to 35 nm with increasing reactant concentration. The magnetic studies show that blocking temperature is enhanced, and these single-domain particles are superparamagnetism at room temperature. The hollow nanospheres exhibit a high saturation magnetization value of 52.6 emu/g. The nanospheres with various diameters exhibit different magnetic saturation values which may be caused by the domain structure, surface effects and the distribution of metal ions on A and B sites. These superparamagnetic Ni0.5Zn0.5Fe2O4nanospheres are expected to have potential application in biomedicine and magnetic fluid technology.

High magnetic field effects on the microstructure and magnetic properties of BaFe 12 O 19 hexaferrites synthesized hydrothermal method have been investigated. The obtained results indicate that the lattice constant decreases gradually as the magnetic field strength increases, which may be attributed to the lattice distortion resulted from the high magnetic field. Polycrystalline BaFe 12 O 19 samples prepared under magnetic field strength at zero and 5 T are single phase. It is found that application of external magnetic field during synthesis can induce orientated growth of the hexaferrite crystals along the easy magnetic axis. The magnetic properties can be effectively regulated by an application of high magnetic fields. It is observed that the BaFe 12 O 19 prepared under a 5 T magnetic field exhibits a higher room-temperature saturation magnetization (66.3 emu/g) than that of the sample (43.6 emu/g) obtained without magnetic field. The results can be explained as the enhanced crystalline, improvement of Fe 3+ ions occupancy and the oriented growth induced by the external magnetic field. The growing orientation of particles gives rise to increased coercivity due to the enhancement in shape anisotropy. It is expected that an application of magnetic field during the formation of magnetic nanoparticles could be a promising technique to modify magnetic properties with excellent performance.

Coaxial heterogeneous chain-like ɑ-Fe/Fe3O4 composites were synthesized by a facile two-step solvothermal method. The ɑ-Fe nanochains were first obtained by a simple liquid phase reduction process, and the ɑ-Fe/Fe3O4 core/shell composites were prepared by subsequent oxidation process. The electromagnetic properties of ɑ-Fe/Fe3O4 core/shell composites were measured with the coaxial reflection/transmission technique at 1.0–18.0 GHz. The ɑ-Fe/Fe3O4 core/shell composites have an optimal absorption peak value of about − 25.6 dB at 16.3 GHz and its effective absorption bandwidth lower than − 10 dB reaches 3.6 GHz (from 14.4 to 18.0 GHz). Importantly, the optimal absorption peak matching thickness of the absorber is only 0.8 mm. The enhanced microwave absorption performance is mainly originated from good impedance matching, which is related to low conductivity and magnetic loss of the coaxial heterogeneous chain-like ɑ-Fe/Fe3O4 core/shell composites. The reflection loss results indicate that the ɑ-Fe/Fe3O4 core/shell composites with thin thickness, wide absorption bandwidth and strong absorption characteristics can be used as excellent microwave absorption material in the high-frequency region.

CeO2/multi-walled carbon nanotubes (CeO2/MWCNTs) composites were successfully synthesized via one-step hydrothermal method. The crystal morphology, structure and electromagnetic parameters of the composites were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, field-emission scanning electron microscopy, high-resolution transmission electron microscopy and vector network analyzer. The microwave absorption performances of CeO2/MWCNTs composites can be evaluated between 2 and 18 GHz frequency range, which is based on transmission line theory. The results demonstrated that fluorite CeO2 nanoparticles were anchored on MWCNTs. The CeO2/MWCNTs composites can reach the minimum reflection loss of − 34.64 dB at 16.24 GHz under the coating thickness of 5 mm, and the frequency bandwidth exceeding − 10 dB was 2.88 GHz. The microwave absorbing properties of the CeO2/MWCNTs composites were mainly attributed to the synergistic effect of dielectric and conductive loss, which were caused by the oxygen vacancies of CeO2. Moreover, charge polarization and interfacial polarization occurring in the composites are beneficial to microwave absorption.

The delafossite CuFeO2 anode materials have been successfully synthesized by hydrothermal process with different temperatures. The X-ray diffraction patterns reveal that two structural polytypes of CuFeO2 with 3R-CuFeO2 and 2H-CuFeO2 are obtained. The results of field-emission scanning electronic microscopy confirm that all CuFeO2 crystals display both hexagonal and rhyombohedral morphologies, which are in good agreement with XRD results. It can be clearly observed that particles sizes of CuFeO2 are increased and the size distributions of particles become broader as hydrothermal temperature increasing. Electrochemical results show that the CuFeO2 particles synthesized at 180 °C for 24 h display the best electrochemical performance and superior cycle performance. The CuFeO2 materials obtained at 180 °C for 24 exhibit a high reversible capacity and high-rate capability (a reversible capability of 390, 276, 185, 133, and 85 mA h g− 1 at 0.1, 0.2, 0.5, 1, 2C, respectively) with good cycling performance (approximate 6.8% capacity loss after 500 cycles at 1C with a capacity retention of 124 mA h g− 1). The excellent electrochemical performance can be attributed to the small particle size and narrow size distributions. It is believed that obtained CuFeO2 crystals as anode materials with high reversible capacity, good rate capability and cyclic stability may be potential candidates for applying in lithium-ion batteries.

The effect of indium doping on structural and magnetic properties of Y-type hexaferrite Ba0.5Sr1.5Zn2(Fe1-xInx)12O22 (x = 0, 0.02, 0.04, 0.06, 0.08 and 0.1) prepared by the solid state reaction method was investigated. The Rietveld refinement method was used to analyze the X-ray diffraction patterns. The magnetic transition temperatures associated with the proper-screw spin phase to the collinear ferrimagnetic spin phase transition can be efficiently modulated by varying indium content. The magnetic transition temperature increases to a maximum with indium content x = 0.04 and then decreases with x, suggesting the possibility that electrically controlled magnetization reversal can be can be effectively tailored by varying indium content. The saturation magnetization at room temperature was decreased as increasing indium content, which can be explained as the metal ions occupation. It is worthy to note that the coercivity of In-doped samples was decreased drastically compared that of undoped sample, which is probably resulted from the reduction in anisotropy field with substitution of In3+ for Fe3+. The In-doped hexaferrite Ba0.5Sr1.5Zn2(Fe1-xInx)12O22 may be potential candidates for application in magnetoelectric devices.

In this work, Metal Organic Frameworks (MOF)-derived the necklace-like carbon nanofibers (CNFs)@carbonaceous Co/CoO composite is synthesized by wet chemical and pyrolysis method. The CNFs are penetrated through the derived carbonaceous Co/CoO frameworks which retain the ZIF-67's sizes. Due to their unique structure and the well controlling of experimental parameters, the optimum reflection loss value of −53.1 dB at 6.56 GHz is obtained, and the corresponding bandwidth below −10 dB (90% absorption) is up to 13.52 GHz with the thickness range of 2.0–5.0 mm. Due to the low density of CNFs and MOF-derived carbon in the composite, the as prepared CNFs@carbonaceous Co/CoO composite can act as a new member of lightweight and high-efficient EM wave absorbents.

Anion engineering on transition-metal-based materials has been put forward as an important strategy to develop efficient and stable non-noble-metal electrocatalysts toward water electrolysis, including both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). On the basis of theoretical predictions, a three-dimensional (3D) integrated electrode constructed by P-decorated Ni3S2 nanosheet arrays (Ni3S2|P) was prepared via a facile two-step method. The suitable controlled incorporation of P anions into the Ni3S2 matrix can have little influence on the crystal structure, and meanwhile can effectively modify the electronic structure, increase the concentration of charge carrier, supply more delocalized electrons, facilitate more active sites to be electrically activated, optimize the hydrogen adsorption Gibbs free energy, strengthen the interaction for water molecules, and benefit the oxidation of Ni2+ to Ni3+ oxo-/hydroxides. As a result, the freshly achieved 3D Ni3S2|P electrode exhibits hi...

Fe3O4/carbon core/shell composites were fabricated via a two-step process. Fe3O4/phenol formaldehyde resin (PFR) core/shell composites were first obtained by hydrothermal method, and the Fe3O4/carb...

To design and synthesize materials for alkaline hydrogen evolution is favorable for industrial hydrogen cycle operation. In this study, we present a facile approach to synthesize free-standing ruthenium-beryllium (RuBe) nanosheets, which possess amorphous phase state and associated with holey structures due to the molten method. The two-dimensional RuBe nanosheets exhibit improved activity than pure Ru counterpart and comparable properties to commercial Pt toward hydrogen evolution reaction in both of alkaline and neutral electrolytes. Based on the experiments and density functional theory calculations, it is suggested that the adsorption and dissociation of water molecules on Ru-based catalyst are much enhanced with the assistance of Be modulation, which are essential for the improved hydrogen production capability under alkaline condition. This work broadens the Ru-based catalyst family and may provide new insights for electrocatalyst development.

The effect of Mg substitution on structural, magnetic, and dielectric properties of Y-type hexaferrite Ba0.5Sr1.5Zn2-xMgxFe11AlO22 (x = 0, 0.4, 0.8, 1.2, 1.6, 2.0) prepared by the solid state reaction method was investigated. The X-ray diffraction patterns are analyzed by Rietveld refinement method and the hexagonal structure with R 3 − m was confirmed. The magnetic transition temperatures associated with the longitudinal conical to proper screw phase transition (T1) and proper screw to ferrimagnetic phase transition (T2) can be modulated by varying Mg content. For x ≤ 1.2 samples, the transition temperature T2 monotonically increases with increasing Mg substitution, suggesting the possibility that the helical spin order of Mg substituted Y-type hexaferrites is sustained up to higher temperatures than that of undoped samples. The saturation magnetization at room temperature increases to a maximum with Mg content x = 1.2 and then decreases with x. The variations of magnetic properties can be attributed to the difference in the preferential site for Zn and Mg and different distribution of Fe3+ ions over tetrahedral and octahedral sites. The results of magnetic field dependence of dielectric constant, i.e., magnetodielectric effect, at various temperatures imply that the doped samples show magnetically induced ferroelectricity up to 250 K. The intrinsic magnetodielectric effect is observed in all the samples. It is worthy to note that the magnetodielectric effect measured below 200 K increases with increasing Mg content, which is probably attributed to the variation of magnetic structures. The Mg-doped hexaferrites Ba0.5Sr1.5Zn2-xMgxFe11AlO22 may be potential candidates for application in magnetoelectric devices.

Highly efficient, economical and environmentally friendly materials are important and remain a challenge in the renewable energy conversion and storage technologies. The oxygen evolution reaction has been envisaged on a two-dimensional graphyne (GY) nanosheet based on density functional theory framework. Local electronic/chemical environment on GY surface is significantly influenced and can be controlled by doping foreign atoms with different formats, which will contribute to its improved catalytic performance. Henceforth, free energy change diagrams, Raman spectra, natural bond orbital charge density, charge density difference, and other data have been calculated and discussed. It is suggested that boron doping at edge sites on GY is the ideal candidate for high OER activity, which is efficient as carbon-based electrocatalysts for water splitting and metal-air batteries.

Multiferroic Y-type Ba2Mg2Fe12O22 (BMFO) hexaferrite, spinel Ni0.5Zn0.5Fe2O4 (NZFO) ferrite, and multi-walled carbon nanotubes (MWCNTs) ternary composites have been successfully fabricated via one-step sol-gel method followed solvothermal method. The electron microscopy analysis exhibits that platelet-like BMFO and quasi-spherical NZFO grains are surrounded by dispersed MWCNTs. The magnetic and microwave absorption (MA) performances are hugely associated with the mass ratio of BMFO to NZFO phase. The saturation magnetization of composites increases from 24.2 to 69.0 emu/g, while permittivity declines apparently with increasing NZFO content. It is easy to infer that the addition of NZFO phase may be beneficial to balance the relative permittivity and permeability of BMFO@NZFO/MWCNTs, which can endow the strong reflection loss of the composites. When the mass ratio of BMFO to NZFO is 3:1, the absorber shows the minimum reflection loss of −36.1 dB at 14.3 GHz with a relatively thin thickness of 1.8 mm, and effective absorption bandwidth (less than −10 dB) of 4.1 GHz. When the mass ratio is reduced to 1:3, the minimum reflection loss reaches to −40.8 dB at 10.6 GHz with an absorber thickness of 2.5 mm, and the effective absorption bandwidth is achieved in the frequency range from 8.0 to 11.9 GHz which covers almost the whole X band (8.0–12 GHz). For the two composites mentioned above, the effective absorption bandwidth covers almost the entire frequency range by changing the absorber thickness from 1 mm to 5 mm. Very interestingly, the effective absorption band shifts to the low frequency by adding NZFO, attributing to adequate exchange-coupling interaction between BMFO and NZFO phases. These mentioned results demonstrate that composites consisting of multiferroic Y-type hexaferrite, spinel ferrite and carbon material have a potential application in high-performance MA materials integrating vigorous absorption intensity, broad absorption bandwidth and thin thickness.

Lightweight, inexpensiveness, easy synthesis, associated with high and broadband absorption are the intensive pursuit for advanced microwave absorbents. Herein, we employ a facile preparation to create holey structures on the wasted biomass-derived carbon materials by air-calcination. All of the carbon absorbents derived from wasted corn cobs, bagasse and grapefruit peels exhibit controlled holey structures on their surfaces, demonstrating the universality of this strategy. The obtained metal-free products are fabricated from bare wasted biomass, without any additional reagents addition. Benefiting from the holey structure generation, more incident microwaves can be consumed due to the increased surface areas and polarization centers for the microwave radiation. The performance measurements suggest the achieved sample could reach a minimum reflection loss value of −47.0 dB at 14.1 GHz and an effective absorption bandwidth (lower than −10 dB) of 5.5 GHz. It is anticipated that this facile holey generation method can be extended to more wasted biomass-derived carbon materials for more sustainable applications.

Metal organic frameworks (MOFs) derived carbonaceous metal oxides and their composite have unique structures and superior properties, thus they have been widely used in various fields. In this study, we use Co based MOFs (ZIF-67) and GO as precursors, synthesize carbonaceous Co3O4/Co/RGO composite as high performance EM wave absorbing materials. The derived carbonaceous Co3O4/Co microframes retain the ZIF-67 nanoparticles’ structure are well dispersed onto the surface of RGO nanosheets. Due to their porous structures and the well controlling of electromagnetic parameters, the obtained composite exhibits a maximum absorption of −52.8 dB at 13.12 GHz, and the bandwidth corresponding to −10 dB (90% absorption) is up to 10.72 GHz (from frequency of 4.88–15.6 GHz) with a coating layer thickness range of 2.0–4.0 mm. Therefore, the synthesized MOF-derived carbonaceous Co3O4/Co/RGO composite is a new promising candidate as highly useful microwave absorbers.

Identifying and generating more active sites with high activity on N-doped graphene for oxygen evolution reaction (OER) are challenging in the renewable energy conversion and storage technologies. However, the local electronic/chemical environment on graphene surface is significantly influenced and can be controlled by doping with foreign atoms, which will contribute to its improved catalytic performance. Henceforth, different N-doping formats, diverse N distributions and concentrations, as well as the edge effect are investigated on the basis of density functional theory, to discover the ideal N-doping condition for high OER behavior. By analyzing the free-energy-change diagrams, adsorbed interactions of reactant intermediates, electrostatic potential surfaces, and other obtained data, it is suggested that graphitic N with low doping concentration and N atoms distributed near edge sites is the ideal candidate for high OER activity, which is efficient as a carbon-based electrocatalyst for water splitting and metal–air batteries applications.

The microstructure and magnetic properties of Mg-doped Ba0.5Sr1.5Zn2Fe12O22 hexaferrites synthesized by the solid state method are investigated. All the undoped and doped samples show a sharp screw proper spin phase to collinear ferrimagnetic spin phase transition above room temperature, and transition temperature increases distinctly with Mg doping. It is noteworthy that all the samples exhibit another magnetic phase transition at a lower temperature T1, which is associated with the longitudinal conical to the proper screw phase transition. The transition temperature T1 can be modulated by varying Mg content, indicating that the longitudinal conical spin phase is stabilized by the Mg-substitution. The saturation magnetization at room temperature increases to a maximum with Mg content x = 0.8 and then decreases with x. The variations of magnetic properties can be ascribed to the difference in the preferential site for Zn and Mg and different distribution of Fe3+ ions over tetrahedral and octahedral sites. It is worth noting that the range for the intermediate-III phase increases significantly as x increases to 2.0, suggesting that Mg-doped samples may be display field-induced ferroelectric order at temperature close to RT and in wide magnetic-field regions. The room-temperature M-H curves at lower applied field indicate that magnetic-field-induced ferroelectric phase can be stabilized at zero magnetic field by the substitution by Mg2+ for Zn2+. The Mg-doped hexaferrites Ba0.5Sr1.5Zn2Fe12O22 may be potential candidates for applying in magnetoelectric devices.

Transparent and conductive Ta doped BaSnO 3 (BaSn 1−x Ta x O 3 , BSTO) films with x = 0–0.15 were epitaxially grown on MgO single crystalline substrates by a pulsed laser deposition method. The effects of Ta ions incorporation on the microstructure, electrical and optical properties of BSTO films were investigated. X-ray diffraction measurements indicate that the out-of-plane lattice parameters increase gradually with Ta concentration increasing, and the films are relaxed due to the large lattice mismatch between the films and substrate. Atomic force microscopy images reveal that all the films have smooth surface and low roughness. X-ray photoelectron spectra of BSTO films confirm that the Ta ions are presented in the +5 state. The lowest room-temperature resistivity and the highest carrier concentration and Hall mobility were observed in BSTO film at x = 0.07, with the values of 2.525 mΩcm, 5.024 × 10 20 cm −3 , and 4.921 cm 2 /Vs, respectively. Temperature dependent resistivity behavior shows that the BSTO films with low doping content exhibit metal-semiconductor transition at low temperature. The optical transmittances of all BSTO films are more than 80% in the visible region. The optical band gaps were found to increase from 3.52 to 4.23 eV with the increase of Ta doping content and can be attributed to the Burstein-Moss effect. Thus, the superior electrical and optical properties of Ta doped BaSnO 3 films are comparable to that of La and Sb doped BaSnO 3 films, and have potential applications in the optoelectronic devices.

For growing high quality epitaxial VO2 thin films, the substrate with suitable lattice parameters is very important if considering the lattice matching. In addition, the thermal conductivity between the substrate and epitaxial film should be also considered. Interestingly, the c-plane of hexagonal 6H-SiC with high thermal conductivity has a similar lattice structure to the VO2 (010), which enables epitaxial growth of high quality VO2 films on 6H-SiC substrates. In the current study, we deposited VO2 thin films directly on 6H-SiC (0001) single-crystal substrates by pulsed laser deposition (PLD) and systematically investigated the crystal structures and surface morphologies of the films as the function of growth temperature and film thickness. With optimized conditions, the obtained epitaxial VO2 film showed pure monoclinic phase structure and excellent phase transition properties. Across the phase transition from monoclinic structure (M1) to tetragonal rutile structure (R), the VO2/6H-SiC (0001) film demonstrated a sharp resistance change up to five orders of magnitude and a narrow hysteresis width of only 3.3 &deg, C.

The NiO/NiCo2O4 mixtures with unique yolk-shell structure were synthesized by a simple hydrothermal route and subsequent thermal treatment. The elemental distribution, composition, and microstructure of the samples were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), and scanning electron microscope (SEM), respectively. The microwave absorption property was investigated by using vector network analysis (VNA). The results indicated that the excellent electromagnetic wave absorption property of the NiO/NiCo2O4 mixtures was achieved due to the unique yolk-shell structure. In detail, the maximum reflection loss (RL) value of the sample reached up to − 37.0 dB at 12.2 GHz and the absorption bandwidth with RL below − 10 dB was 4.0 GHz with a 2.0-mm-thick absorber. In addition, the NiO/NiCo2O4 mixtures prepared at high temperature, exhibited excellent thermal stability. Possible mechanisms were investigated for improving the microwave absorption properties of the samples.

The Co and Ti co-doped SrFe12O19 hexaferrites have been successfully synthesized via the sol–gel method. The X-ray diffraction patterns demonstrate that all doped samples are single-phase hexagonal crystal confirmed by Rietveld refinement. The results of field-emission scanning electronic microscopy reveal that the particle sizes increase obviously with increasing Co–Ti substitution rate. It can be clearly observed that the magnetic properties can be effectively tuned by the partial substitution of Fe with Co and Ti. The magnetization measurement manifests both saturation magnetization and coercivity drop with increasing Co–Ti concentration. Specifically, the coercivity falls substantially from about 1697 to 20 Oe with only a little decrease in the saturation magnetization as x increases from 0.5 to 1.5. The results indicate that low-doped Co–Ti substitution rates (x) make hexaferrites suitable for high density and perpendicular recording technology. It is worthy to note that the Co–Ti substituted samples can gradually turn the magnetocrystalline anisotropy from uniaxial to planar, and the transition point is near x = 1.5, which is beneficial to the formation of a conical magnetic structure to induce electric polarization. It is expected that Co–Ti co-doped hexaferrite Sr(CoTi)1.5Fe9O19 may be potential candidates for application based on the magnetoelectric devices.

Bio-derived dielectrics have drawn extensive attention for microwave absorption and shielding because of renewability and environmental friendliness. In this work, foam-like bio-carbon has been obtained from wheat straw waste and its microwave absorption performance has been studied. By controlling the precursor ratio of KOH, the optimized morphology of bio-carbon has been realized. The 3D carbon foam obtained at 600 °C with KOH and biomass ratio 1:1 (AC-600 (1:1), presents decent microwave reflection loss. Especially, with a low absorber ratio (10 wt%), the effective absorption bandwidth (RL

By utilizing magneto-optical microscopy combined with the polar magneto-optical Kerr effect (MOKE) techniques, the photo-induced melting and quenching effects on magnetic domains in a quasi-two-dimensional (quasi-2D) ferromagnetic Cr5Te8 crystal were investigated. With irradiation of a pulsed laser, the magnetic domain of the Cr5Te8 crystal can be melted at a critical laser power density (2.55 × 108 mW/cm2), which has been confirmed by both MOKE images and curves. Moreover, it is intriguing to find that after laser melting and quenching, the dendritic type domains of the Cr5Te8 crystal are broken and the regrown spherical type domains are isolated from the original dendrites. Simultaneously, the magnetization behavior as a function of external field was modulated. These findings suggest that laser melting and quenching is an effective technique to tailor the magnetic domains in quasi-2D magnets and it provides a viable route in the creation of optical spintronic devices.

Here, we synthesized LaNiO3 microspheres by a simple hydrothermal synthesis and subsequent annealing process. The LaNiO3 microspheres are characterized by TG-DSC, XRD, FESEM, TEM and VAN. Noticeably, owing to the effective synergism between significant dielectric loss and optimum impedance match, LaNiO3 microspheres exhibit significantly remarkable attenuation capability and wide-band respond. Therefore, the possible mechanism of microwave absorption enhancement is carefully investigated. A minimum reflection loss intensity −30.6 dB of LaNiO3 microspheres can be achieved and a broad effective absorbing bandwidth (reflection loss reaches −10.0 dB) of 4.72 GHz (8.16–12.88 GHz) at the thickness of 2.0 mm. Furthermore, the overall effective bandwidth is obtained up to 14.5 GHz from 3.5 GHz to 18 GHz, covering more than 90% of the measured frequency range. It is expected that the LaNiO3 microspheres could be used to design efficient microwave absorption materials.

Reduced graphene oxide (RGO) nanosheets normally possess large specific surface area, good electrical conductivity, and low density, but their unsatisfactory intrinsic complex permittivity and poor impedance matching severely hinder the further application in microwave adsorption. In this work, borophene nanosheets (BNS), the lightest 2D material, are proposed as an efficient activator to improve the microwave absorbing performance on RGO. BNS are assembled and immobilized on RGO surface through the interfacial covalent interaction, to construct a new metal-free 2D hybrid absorbent. These incorporated BNS serves as the joining site and channel in the framework to facilitate electrons hopping and migration between RGO layers. As a result, conductive loss mechanism is well enhanced, which is the major contribution to its dielectric property, conferring high impedance matching on the absorbent. As expected, the as-obtained 2D metal-free hybrid demonstrates microwave absorbing parameters that approach those of the most active absorbents, with the minimum reflection loss reaching −53.3 dB and the broadest effective absorption bandwidth of 6.16 GHz, at a low filler loading of 3 wt%.

A novel kind of microwave absorption composite in Ku-band with low cost, low density and strong absorption was prepared through Bio-template carbonization and solvothermal method. The phase structures and morphologies of the composite had been characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The microwave absorption properties of carbonized kapok fibers and Fe3O4/kapok fibers were measured by vector network analysis (VNA). When the sample thickness is 1.5 mm, the Fe3O4/kapok fibers have an optimal absorption peak value of about −24.1 dB at 17.4 GHz and its effective absorption bandwidth lower than −10 dB reaches 2.4 GHz (from 15.6 to 18.0 GHz). The reflection loss results indicate that the Fe3O4/kapok fibers possess higher microwave absorption in the Ku-band. A possible mechanism of the improved microwave absorption performance of the composite was discussed.

Over a long period of time, single iron oxide (Fe2O3) or cobalt oxide (Co2O3) has been extensively studied for magnetic absorbing materials. Recently, some nanoscale compounds composed of two ferrites have been reported for better electromagnetic absorbing properties because of collectively corporation. However, there are few reports about other magnetic absorbing materials. In addition, morphology control for better absorbing performance remains challenging. Here, the monodispersed, uniform rod-shaped FeCO3/CoCO3 microparticles are successfully synthesized by a facile one-step solvothermal method for the first time. The experimental results show that the reflection loss (RL) value of the paraffin composites with thickness of 2.0 mm is less than −10 dB in the frequency range of 6.72–15.92 GHz and the minimum RL value of −31.86 dB at 12.88 GHz is obtained, which demonstrates that the as-prepared FeCO3/CoCO3 microparticles have excellent magnetic and microwave absorbing properties.

Many nanomaterials have been widely reported for removal of toxic inorganic metal ions. However, some nanoscale adsorbents are subject to serious aggregation. For example, it is very difficult to directly synthesize the monodispersed Fe(OH) 3 nanomaterials. Here, through using the monodispersed hierarchical γ-Al 2 O 3 nanoflowers as adsorbent supports, the Fe(OH) 3 colloid nanoparticles have been well deposited onto the surfaces of the hierarchical γ-Al 2 O 3 nanostructures to form γ-Al 2 O 3 /Fe(OH) 3 composites with hierarchical structures via an electrostatic attraction without forming large aggregates. The γ-Al 2 O 3 /Fe(OH) 3 composites with hierarchical structures have high specific surface areas and large pore volumes, which are used as adsorbents to remove anion species of As(V) and Cr(VI) from aqueous solution. The maximum capacities of the monodispersed γ-Al 2 O 3 /Fe(OH) 3 composites with hierarchical structures for As(V) and Cr(VI) are determined at 61.99 mg g −1 and 24.13 mg g −1 , respectively, which are higher than those of the other metal oxide nanostructures reported. In addition, the adsorption rates of As(V) and Cr(VI) onto the monodispersed γ-Al 2 O 3 /Fe(OH) 3 composites with hierarchical structures are rather fast. The γ-Al 2 O 3 /Fe(OH) 3 hierarchical micro/nanoflower structures show high adsorption capacity for removing anion species of As(V) and Cr(VI), demonstrating a promising potential in environmental remediation.

Many nanomaterials have been reported for the removal of toxic inorganic metal ions. Some conventional micro- or nano-structured adsorbents are subject to serious aggregation. Here, well-dispersed, Fe(OH)3 colloid nanoparticles have been effectively deposited onto the surfaces of hierarchical γ-AlOOH nanostructures to form γ-AlOOH/Fe(OH)3 with hierarchical structures via an electrostatic attraction without forming large aggregates. The monodispersed γ-AlOOH/Fe(OH)3 with hierarchical structures have high specific surface areas and large pore volumes, which are used as adsorbents to remove anion species of As(V) and Cr(VI) from aqueous solution. The maximum capacities of the monodispersed γ-AlOOH/Fe(OH)3 with hierarchical structures for As(V) and Cr(VI) in this study are determined at 43.8 mg g−1 and 13.1 mg g−1, respectively, which are higher than those of the other metal oxide nanostructures reported to date. In addition, the adsorption rates of As(V) and Cr(VI) onto the monodispersed γ-AlOOH/Fe(OH)3 with hierarchical structures are rather fast. The γ-AlOOH/Fe(OH)3 hierarchical micro/nanoflower structures show high adsorption capacity for removing the anion species of As(V) and Cr(VI), demonstrating a promising potential in environmental remediation.