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We investigate interface regulation of amorphous boron and cotton pads to experimentally verify their performance in solar steam generation. Thanks to the superabsorbent cotton pads and the construction design, unobstructed water flow is achieved.

The exploitation of multicomponent nanocomposites with suitable hierarchical heterostructures is an attractive strategy to obtain high performance microwave absorption materials. In this work, a versatile strategy is proposed for synthesizing 1D hierarchical core-shell structure with Co-ZIF arrays derived carbon nanotubes (CNTs) coupled on cotton fiber (CF)-supported MXene shell (Co/CNTs-MXene@CF). The advantages of Co-ZIF arrays derived CNTs and MXene dielectric layer can be efficiently integrated to realize multiple electron transfer paths by the construction of the well-designed hierarchical structure. The designed heterogeneous composites consist of the interlayer MXene and CNTs grow sequentially from the outermost Co-ZIF nanosheet arrays with appropriate conductivity and abundant heterointerfaces, which can improve the conduction loss and interfacial polarization response. As expected, the elaborate 1D Co/CNTs-MXene@CF heterostructures exhibit the optimal reflection loss of −61.41 dB at 2.52 mm and effective absorption bandwidth reaches 5.04 GHz with a thickness of only 1.5 mm. The experimental results demonstrate that the optimized structure dramatically improves the electromagnetic wave attenuation behavior. This work illuminates a new design strategy for the preparation of multicomponent composites with reasonable hierarchical structure that enables high-performance microwave absorption materials.

Graphene-based metal-free aerogel is desirable for lightweight electromagnetic wave (EMW) absorbing materials. However, the weak van-der-Waals combination between graphene sheets, accompanied by the repulsion from surface oxygen-related polar groups, significantly hinder the transfer of electrons between the sheets, and lead to poor mechanical strength. These become bottlenecks for the further improvement of EMW absorption and have a huge impact on achieving multi-functions. Here, we used an iodine modification strategy to fabricate reduced graphene oxide (RGO) aerogel, in which graphene sheets are bridged by iodine cations (I+). Meanwhile, iodine promotes the conversion of epoxy groups to hydroxyl groups on graphene, thereby facilitating the adhension of I+ on the surface. These iodine cations rather than iodine anions are essential to strengthen the interconnection between graphene sheets, which enables the RGO aerogel to exhibit higher electrical conductivity, larger mechanical strength, higher thermal stability, and significantly improved EMW absorbing capability. With the improvement in conduction loss and impedance matching, the iodine-bridged RGO aerogel exhibits a maximium reflection loss of −52.8 dB and an effective absorption bandwidth of 7.2 GHz at 2 wt% filler loading, which are 3.8 and 1.5 times of pure RGO, respectively. Besides, the improved mechanical strength and resistance to temperature change benefit expanding the application fields of this aerogel.

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.

Fe-modified Ru nanosheets are achieved via preintercalated Al species serving as the self-sacrificial template. Benefiting from the amphoteric feature of Al and strong corrosion of Fe

Micro/nanocarbon materials have been regarded as one of the most desirable microwave absorbents due to their unique physical and chemical properties, whereas their unsatisfactory intrinsic complex permittivity and poor impedance matching severely hinder the further application in microwave adsorption. Herein, novel sulfur-doped hollow carbon microtubes (S-HCMTs) are successfully prepared through a facile one-step pyrolysis process using poplar catkin as a carbon precursor and sulfur powder as a doping agent. The poplar catkin-derived carbon materials exhibit a novel hollow microtubular structure, which is hard to be realized by the conventional chemical synthesis, and meanwhile the one-dimensional hollow structure can be well preserved after the sulfur doping treatment. Note that the introduction of sulfur atoms is beneficial to the adjustment of the electrical conductivity, thereby leading to superior impedance matching characteristics and dipolar relaxation loss capacity in comparison with pure hollow carbon microtubes (HCMTs). The as-obtained S-HCMTs exhibit excellent microwave absorption performance. The minimum reflection loss (RLmin) of S-HCMTs is as high as − 37.4 dB at 6.72 GHz, and the broadest effective absorption bandwidth reaches 8.0 GHz. The high-efficiency microwave absorption is mainly originated from the unique hollow structures, enhanced dipolar/interfacial polarization, multiple scatterings, as well as the excellent impedance match. The results demonstrate that the S-HCMTs can be considered as a promising candidate in high-performance microwave absorbers integrating lightweight and strong absorption intensity.

Metal-free hybrids possess many advantages when compared with metal-based materials, such as lightweight, low cost, and high stability, which offer great potential for them to be used in wide applications, such as microwave absorption. Bare carbon materials, especially for those derived from wasted biomass, normally cannot simultaneously exhibit strong and broadband absorption performance, due to their specific structures and high electronic conductivity, leading to more incident microwave reflected on surface. Herein, based on wasted grapefruit peels, 2D metal-free hybrids are designed and prepared with pre-exfoliated boron nanoflakes as the modulation. Noncovalent interaction is formed at their heterojunction, which endows them with properties that cannot be supplied by their individual components. As a result, interfacial polarizations and dipole polarizations are generated between the layers, benefiting the dielectric loss and impedance matching behaviors. Microwave absorption measurements demonstrate that the minimum reflection loss can reach − 47.9 dB and the effective absorption frequency band is 4.32 GHz, at 1.5 mm thickness. We hope these represent an addition to the family of sustainable biomass-derived microwave absorbents.

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.

The porous Fe3O4 nanorods have been successfully fabricated via a facile and energy-efficient hydrothermal method based on SiO2-coated β-FeOOH nanorods as a precursor. The effect of SiO2 coating on the phase structure and morphology of as-prepared samples have been systematically characterized by X-ray diffraction, scanning electron microscopy (SEM) and transmission electron microscope (TEM). SEM and TEM results reveal that the Fe3O4 nanorods possess one-dimension configuration and the porous structure. The complex permittivity and permeability of the sample are studied in the frequency range of 2.0–18.0 GHz with 55 wt% of porous Fe3O4 nanorods in paraffin. For the Fe3O4 nanorods, the maximum reflection loss (RL) is − 41.5 dB at 10.24 GHz and the effective absorption bandwidth below − 10 dB can achieve 5.2 GHz (9.28–14.48 GHz) with a matching thickness of 2.4 mm. The enhanced microwave absorption performance is mainly originated from multi-reflection between nanorods and interface polarization, which is related to special rod configuration and the porous structure of the porous Fe3O4 nanorods. This work proposes a promising method to tune the microwave absorption performance via morphology control.

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...

Cu-based electrocatalysts for overall water splitting are less reported. Room-temperature synthesis of cost-effective Cu electrodes to replace precious catalysts remains a great challenge. Herein, ...

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 lanthanum doping barium stannate nanoparticles have been fabricated facially via a wet chemical reaction and subsequent annealing process. The thermal decomposition, phase purity, morphology and microstructure are characterized by thermo-gravimetric (TG) and differential scanning calorimetric (DSC), powder X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The microwave absorption properties of Ba1−xLaxSnO3 (x = 0, 0.02, 0.04 and 0.06) nanoparticles are carried out by vector network analyzer (VNA). The results reveal that the Ba1−xLaxSnO3 (x = 0.02, 0.04 and 0.06) nanoparticles exhibited enhancement of microwave absorption performance compared with the pure BaSnO3. For sample with x = 0.02, the minimum reflection loss reaches − 43.78 dB at 13.6 GHz and its effective absorption bandwidth lower than − 10 dB reaches 3.12 GHz. And there are two absorption peaks at 9.36 and 10.64 GHz with the minimum reflection loss is − 30.11 and − 31.30 dB, and the bandwidth of lower than − 10 dB can reach up to 3.12 GHz. It means that BaSnO3 by doping of La ions can be used as an excellent microwave absorption material.

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 article, the CoFe2O4/MoS2 composites have been well constructed via a facial hydrothermal method, from which the porous CoFe2O4 microspheres were embedded into MoS2 ultrathin nanosheets. As a typical two-dimensional transition metal sulfide, MoS2 with high electrical conductivity and flexible properties is expected to exhibit high dielectric loss and magnetic loss when combined with magnetic material CoFe2O4. Meanwhile, the unique hierarchical structure of as-synthesized MoS2 nanoflowers is conducive to scattering and reflection of electromagnetic waves, and endows designed composites with competitive microwave absorption properties. Notably, although the saturation magnetization of MoS2/CoFe2O4 composites is significantly decreased compared to pure CoFe2O4 microspheres, the coercivity still maintains a high value of 626.1 Oe. As expected, the results demonstrate that as-fabricated MoS2/CoFe2O4 composites do have superior microwave absorption properties in comparison with CoFe2O4 and MoS2. It is found that the complex permittivity is enhanced with increasing filling ratio from 45 wt% to 60 wt%, which is helpful for obtaining a moderate permittivity value. When the filling ratio is 50 wt%, the MoS2/CoFe2O4 composites exhibit a minimum reflection loss (RLmin) of − 53.1 dB at 12.08 GHz when the thickness is 2.5 mm. An effective absorption bandwidth less than − 10 dB of 6.61 GHz from 11.28 to 17.89 GHz is achieved with a thin thickness of 2.2 mm, almost covering the whole Ku-band. The improvement in microwave absorption properties can be ascribed to the synergistic effect of the magnetic CoFe2O4 and dielectric MoS2. The impedance matching characteristic and interfacial polarization are significantly optimized by inserting CoFe2O4 spheres onto the surface of MoS2 nanosheets. Considering the excellent performance of as-fabricated MoS2/CoFe2O4 composites, it is believed that the MoS2-based composites can be applied as a promising candidate of highly effective microwave absorbers with strong absorption intensity and broad absorption frequency.

Identifying the active sites on graphene oxide (GO) nanosheets is of great importance. In situ electroreduction at different potentials is applied to control the oxygenated groups on GO surfaces. Both experiments and theoretical calculations suggest the C═O group is critical for N2 adsorption and activation, guaranteeing the ambient electrocatalytic N2 reduction.

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.

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

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.