Facile synthesis of hierarchical chrysanthemum-like copper cobaltate-copper oxide composites for enhanced microwave absorption performance

Colorimetric array sensor based on bimetallic nitrogen-doped carbon-based nanozyme material to detect multiple antioxidants

Copper-cobalt bimetallic nitrogen-doped carbon-based nanoenzymatic materials (CuCo@NC) were synthesized using a one-step pyrolysis process. A three-channel colorimetric sensor array was constructed for the detection of seven antioxidants, including cysteine (Cys), uric acid (UA), tea polyphenols (TP), lysine (Lys), ascorbic acid (AA), glutathione (GSH), and dopamine (DA). CuCo@NC with peroxidase activity was used to catalyze the oxidation of TMB by H2O2 at three different ratios of metal sites. The ability of various antioxidants to reduce the oxidation products of TMB (ox TMB) varied, leading to distinct absorbance changes. Linear discriminant analysis (LDA) results showed that the sensor array was capable of detecting seven antioxidants in buffer and serum samples. It could successfully discriminate antioxidants with a minimum concentration of 10 nM. Thus, multifunctional sensor arrays based on CuCo@NC bimetallic nanoenzymes not only offer a promising strategy for identifying various antioxidants but also expand their applications in medical diagnostics and environmental analysis of food.

A Regulable Polyporous Graphite/Melamine Foam for Heat Conduction, Sound Absorption and Electromagnetic Wave Absorption

To reduce electromagnetic interference and noise pollution within communication base stations and servers, it is necessary for electromagnetic wave absorption (EWA) materials to transition from coating to multifunctional devices. Up to now, the stable and effective integration of multiple functions into one material by a simple method has remained a large challenge. Herein, a foam-type microwave absorption device assembled with multicomponent organic matter and graphite powder is synthesized by a universal combination process. Melamine and phenolic aldehyde amine work as the skeleton and cementing compound, respectively, in which graphite is embedded in the cementing compound interconnected into the mesoscopic 3D electric conductive and heat conductive network. Interestingly, the prepared flexible graphite/melamine foam (CMF) delivers a great EWA performance, with a great effective absorption bandwidth of 9.8 GHz, ultrathin thickness of 2.60 mm, and a strong absorption reflection loss of -41.7 dB. Moreover, the CMF possesses porosity and flexibility, endowing it with sound absorption ability. The CMF is unique in its integration of EWA, heat conduction, sound absorption, and mechanical robustness, as well as its cost-effective and scalable manufacturing. These attributes make CMF promising as a multifunctional device widely used in communication base stations, servers, and chips protection.

Simple fabrication of cobalt-nickel alloy/carbon nanocomposite fibers for tunable microwave absorption

A series of CoNi/C nanocomposite fibers with different Co and Ni ratios were successfully prepared by electrospinning and carbonization techniques for the study of electromagnetic microwave (EMW) absorbing materials. We systematically studied the influence of Co and Ni content on the microstructure, chemical composition, magnetic properties, and EMW absorption characteristics of the samples. The results showed that CoNi/C nanocomposite fibers obtained excellent EMW absorption ability through the reasonable design of the composition, and the Co/Ni ratio significantly affected the microstructure and EMW absorption performance. When the Co/Ni ratio was 1/3, the minimum reflection loss (RLmin) is -71.2 dB (2.4 mm, 13.4 GHz), and the maximum effective absorption bandwidth (EAB, RL＜-10 dB) is up to 5.9 GHz (2.2 mm, 12.1-18 GHz), covering almost the entire Ku band. This study demonstrated the enormous potential of one-dimensional structure in the field of EMW absorption. In addition, the CoNi/C nanocomposite fiber synthesized using a straightforward and low-cost method not only has excellent EMW absorption performance but also has the potential for practical application. The results of this study provide a simple and effective approach for designing high-performance EMW absorbing materials.

Impact mechanisms of aggregation state regulation strategies on the microwave absorption properties of flexible polyaniline

In the field of electromagnetic (EM) wave absorption, intrinsic conductive polymers with conjugated long-chain structures, such as polyaniline (PANI) and polypyrrole (PPy), have gained widespread use due to their remarkable electrical conductivity and loss ability. However, current research in this area is limited to macroscopic descriptions of the absorption properties of these materials and the contribution of various components to the absorption effect. There has been insufficient exploration of the impact mechanisms of polymer aggregation states on the material's absorption performance and mechanism. To address this, a series of flexible PANI sponge absorbers with different molecular weights and aggregation states were prepared. By carefully controlling the crystallinity and other aggregation characteristics of PANI through the adjustment of its preparation conditions, we were able to influence its electrical conductivity and electromagnetic parameters, thereby achieving control over the material's absorption properties. The resulting PANI sponge absorbers exhibited an effective absorption bandwidth (EAB) that covered the entire X-band at a thickness of 3.2 mm. This study comprehensively explores the absorption mechanisms of conductive polymer absorbers, starting from the microstructure of PANI, and providing a more complete theoretical support for the research and promotion of polymer absorbers.

A Bifunctional Catalyst for Green Ammonia Synthesis from Ubiquitous Air and Water

Ammonia (NH3 ) is essential for modern agriculture and industry, and, due to its high hydrogen density and no carbon emission, it is also expected to be the next-generation of "clean" energy carrier. Herein, directly from air and water, a plasma-electrocatalytic reaction system for NH3 production, which combines two steps of plasma-air-to-NOx - and electrochemical NOx - reduction reaction (eNOx RR) with a bifunctional catalyst, is successfully established. Especially, the bifunctional catalyst of CuCo2 O4 /Ni can simultaneously promote plasma-air-to-NOx - and eNOx RR processes. The easy adsorption and activation of O2 by CuCo2 O4 /Ni greatly improve the NOx - production rate at the first step. Further, CuCo2 O4 /Ni can also resolve the overbonding of the key intermediate of * NO, and thus reduce the energy barrier of the second step of eNOx RR. Finally, the "green" NH3 production achieves excellent FENH3 (96.8%) and record-high NH3 yield rate of 145.8 mg h-1  cm-2 with large partial current density (1384.7 mA cm-2 ). Moreover, an enlarged self-made H-type electrolyzer improves the NH3 yield to 3.6 g h-1 , and the obtained NH3 is then rapidly converted to a solid of magnesium ammonium phosphate hexahydrate, which favors the easy storage and transportation of NH3 .

Lightweight electromagnetic wave absorbent composites with Fe3O4 nanocrystals uniformly decorated on the surface of carbon spheres

The application of electromagnetic waves has reached every aspect of human life, but the search for superior electromagnetic wave absorbent materials has been a constant quest of researchers. The application of heterogeneous structures has been favored by researchers of electromagnetic wave absorbent materials and the quest for simple preparation methods and homogeneous distribution of heterogeneous structures is continuing. In this study, we synthesized carbon sphere/Fe₃O₄ nanocrystal (CS/Fe₃O₄) composites by uniformly decorating Fe₃O₄ nanoparticles on the surface of carbon spheres through a simple strategy of expanding the heterogeneous structured interface. The heterogeneous interface formed by graphite and amorphous carbon in the carbon spheres is a boundary-type defect and combined with the magnetic loss capability of the Fe₃O₄ nanocrystals, this composite material has excellent electromagnetic wave absorption properties. The composite material synthesized with 0.05 M solution of iron nitrate has the best electromagnetic wave absorption performance of all samples due to the synergistic effect of interfacial polarization, eddy current loss, defect engineering, and magnetic energy attenuation capability. Reflection losses of -50.932 dB and -49.143 dB were achieved at 4.65 GHz and 10.6 GHz respectively, corresponding to thicknesses of 3.74 mm and 1.74 mm. In addition, the widest effective absorption bandwidth (EAB) at 1.27 mm was 4.5 GHz (13.50-18 GHz). This study enhances the electromagnetic wave absorption performance of carbon spheres by surface-decorating Fe₃O₄ nanoparticles, solves the problem of homogeneity of decorative magnetic oxides on the surface of carbon-based materials, and provides new ideas for the design of controllable, lightweight, ultra-thin composites of carbon-based electromagnetic wave absorbent materials that possess strong electromagnetic wave absorption capability.

Synergy effect of CuO on CuCo2O4 for methane catalytic combustion

Spinel oxides (AB₂O₄) have been widely studied as catalysts for methane combustion. Increasing attention was focused on the catalysis properties of the [B₂O₃] octahedron; however, the role of the [AO] tetrahedron in the catalytic activity was seldom discussed. Herein, a series of (CuO)_x–CuCo₂O₄ (x = 0, 0.1, 0.2) composite oxides were synthesized by a solvothermal method. The structure, morphology, and physicochemical properties of the as-synthesized samples were characterized by the XRD, SEM, BET, and XPS techniques. The results of the catalytic activity tests showed that the coexistence of CuO with CuCo₂O₄ can improve the catalytic activity. The XPS results demonstrated that there were remarkable Cu⁺ ions present in the composite oxides, which can cause increases in the number of oxygen vacancies on the surface of the catalysts. In addition, the redox of Cu⁺ and Cu²⁺ may improve the oxygen exchange capacity for methane oxidation.

CuO and CuCo₂O₄ exhibit a synergistic effect in catalyzing methane combustion, which increases the oxidation rate of methane on the surface of (CuO)_0.2–CuCo₂O₄ composite oxide and decreasing the methane combustion temperature.

Transferring A4 Paper to FeNi3/NiCx Coated Carbon Skeleton for Efficient Absorption of Multiband Microwave

Herein, A4 typing paper was used as a novel source to manufacture FeNi3 and NiCx coated carbon skeleton via facile routes. The product was examined for its ability to absorb electromagnetic emission which can be a health hazard. The impact of precursor concentration on the final electromagnetic wave absorption of samples was evaluated; the composite prepared under suitable concentration possesses outstanding multiband absorption ability of −34.64 dB and −26.7 dB at 2.32 GHz and 17.2 GHz, respectively, together with an ultra-wide effective absorption bandwidth of 9.58 GHz at only 3.9 mm. The strong dipole polarization and broad frequency range of preferable impedance matching, along with the coupling of other auxiliary mechanisms, are responsible for this excellent property. The as-prepared absorber has great potency for multiband absorption of electromagnetic waves.

Enhanced catalytic performance of spinel-type Cu-Mn oxides for benzene oxidation under microwave irradiation

Microwave-assisted heterogeneous catalytic oxidation of benzene was investigated over Cu-Mn spinel oxides. The spinel oxides were synthesized by a coprecipitation method from metal nitrate hydrolysis in a solution using tetramethylammonium hydroxide (TMAH) as a precipitation reagent. The catalysts were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, X-ray absorption fine structure, scanning electron microscopy, transmission electron microscope and H₂-temperature-programmed reduction studies. Microwave absorption by the Cu-Mn spinel oxide is mainly driven by dielectric losses (dielectric heating). Cu-Mn spinel oxide with a Cu/Mn ratio of 1 exhibited superior activity to single oxides under microwave heating, demonstrating lower apparent activation energy than that obtained under conventional heating. Microwave irradiation lowered the reaction temperature required for benzene oxidation compared with conventional heating. Transient tests were used to investigate the reactivity of oxygen species in the catalytic reaction, and the high reactivity of Cu-Mn spinel oxides was related to the high reactivity of lattice oxygen on the catalyst surface. The reactivity of the oxygen species was enhanced under microwave heating, leading to an enhanced benzene oxidation reaction. The combination of adsorption and catalytic oxidation processes using Cu-Mn spinel oxides and zeolites efficiently decomposed benzene at low concentrations.

Lightweight, Low-Cost Co2SiO4@diatomite Core-Shell Composite Material for High-Efficiency Microwave Absorption

The porous and biomimetic cobalt silicate@diatomite (Co2SiO4@diatomite) was successfully synthesized by a two-step method, including the hydrothermal method and calcination to improve the electromagnetic wave absorption property. Different hydrothermal times were well-tuned for Co2SiO4@diatomite composites with different loadings of Co2SiO4. Interestingly, the Co2SiO4@diatomite composites (6 h, 25 wt%) had a smaller minimum reflection loss. Moreover, the minimum reflection loss (RLmin) could reach -12.03 dB at 16.64 GHz and the matched absorber thickness was 10 mm, while the effective absorption bandwidth (EAB, RL ≤ -10 dB) could be 1.92 GHz. In principle, such findings indicate that Co2SiO4@diatomite nanocomposites could be a promising candidate for high-efficiency microwave absorption capability.

Porous magnetic carbon CoFe alloys@ZnO@C composites based on Zn/Co-based bimetallic MOF with efficient electromagnetic wave absorption

To obtain lightweight and efficient electromagnetic wave absorbing materials, Fe₂O₃@ZnCo-MOF composites were prepared in this paper by in-situ growth method, and CoFe alloys@ZnO@C composites were obtained by subsequent annealing process. By varying the loading of Fe₂O₃ during the synthesis process, a series of composites were obtained. Among them, CoFe alloys@ZnO@C-0.1 has the best electromagnetic wave absorption performance, which can reach a reflection loss (RL) of -40.63 dB at a thickness of 2.2 mm, while the reflection loss is -44.13 dB at a thickness of 5.0 mm, and the maximum effective absorption bandwidth (EAB) is 5.84 GHz at a thickness of 2.4 mm. The excellent performance can be attributed to the synergistic effect of the dielectric and magnetic properties of the composites as well as the effective impedance matching properties. Thus, the CoFe alloys@ZnO@C composite is expected to be a lightweight and efficient material for electromagnetic wave absorption.

Ultralight and High-Strength SiCnw@SiC Foam with Highly Efficient Microwave Absorption and Heat Insulation Properties

An ultralight and high-strength SiC_nw@SiC foam with highly efficient microwave absorption and heat insulation properties was successfully synthesized using the template sacrifice method and chemical vapor deposition process. The microstructure is a novel double network structure, which is formed by the coupling of the morphology-controlled SiC_nw and the SiC skeleton. The introduction of SiC_nw can not only provide more interface polarization and dielectric loss to the SiC foam, which greatly enhances the microwave absorption capacity of the composite foam, but also can enable it to act as an excellent radiation absorbent, which can effectively reduce the thermal conductivity of the foam, especially at high temperatures. In this study, a minimum reflection loss (RL_min) of -52.49 dB was achieved at 2.82 mm thickness with an effective absorption bandwidth of 5.6 GHz. As the length/diameter ratio of SiC_nw decreases, the composite foam exhibits excellent high-temperature thermal insulation and mechanical properties. For the SiC_nw@SiC foam, the thermal conductivity is only 0.304 W/mK at 1200 °C and the compressive strength reaches 1.53 MPa. This multifunctional SiC_nw@SiC foam is an outstanding material, which has potential applications in microwave absorption and high-temperature heat insulation in harsh environments.

Constructing core-shell structured BaTiO3@carbon boosts piezoelectric activity and cell response of polymer scaffolds

Piezoelectric composites have shown great potential in constructing electrical microenvironment for bone healing since their integration of polymer flexibility and ceramic piezoelectric coefficient. Herein, core-shell structured BaTiO₃@carbon (BT@C) hybrid nanoparticles were prepared by in situ oxidative self-polymerization and template carbonization. Then the BT@C was introduced into polyvinylidene fluoride (PVDF) scaffolds manufactured by selective laser sintering. On one hand, the carbon shell could strengthen the local electric field loaded on BT in poling process owing to it served as a diffusion layer to provide space for charge transfer and accumulation. In this case, more electric domain within BT would be aligned along the polarization field direction and thus promoted the paly of BT's piezoelectric activity. On the other hand, the carbon shell could induce the formation of β phase due to the sp² hybrid-bonded carbon atoms in carbon shell forming electrostatic interaction with hydrogen atoms in PVDF chains, which further enhanced the piezoelectric response of the scaffolds. Results showed that the scaffold presented augmented piezoelectric performance with output voltage of 5.7 V and current of 79.8 nA. The improved electrical signals effectively accelerated cell proliferation and differentiation. Furthermore, the scaffold displayed improved mechanical performance due to rigid particle strengthen effect.

Fabrication of N-Doped Reduced Graphite Oxide/MnCo2O4 Nanocomposites for Enhanced Microwave Absorption Performance

The present work reports on the fabrication of a lightweight microwave absorber comprising MnCo₂O₄ prepared from the urea complex of manganese (Mn)/cobalt (Co) and nitrogen-doped reduced graphite oxide (NRGO) by facile hydrothermal method followed by annealing process and characterized. The phase analysis, compositional, morphological, magnetic, and conductivity measurements indicated dispersion of paramagnetic MnCo₂O₄ spherical particles on the surface of NRGO. Our findings also showed that Mn, Co-urea complex, and GO in the weight ratio of 1:4 (NGMC3) exhibited maximum shielding efficiency in the range of 55-38 dB with absorption as an overall dominant shielding mechanism. The reflection loss of NGMC3 was found to be in the range of -90 to -77 dB with minima at -103 dB (at 2.9 GHz). Such outstanding electromagnetic wave absorption performance of NRGO/MnCo₂O₄ nanocomposite compared to several other metal cobaltates could be attributed to the formation of percolated network assisted electronic polarization, interfacial polarization and associated relaxation losses, conductance loss, dipole polarization and corresponding relaxation loss, impedance matching, and magnetic resonance to some extent.

Fabrication, Optimization and Characterization of Paclitaxel and Spirulina Loaded Nanoparticles for Enhanced Oral Bioavailability

Background:

Paclitaxel and spirulina when administered as nanoparticles, are potentially useful.

Methods:

Nanoformualtions of Paclitaxel and Spirulina for gastric cancer were formulated and optimized with Central composite rotatable design (CCRD) using Response surface methodology (RSM).

Results:

The significant findings were the optimal formulation of polymer concentration 48 mg, surfactant concentration 45% and stirring time of 60 min gave rise to the EE of (98.12 ± 1.3)%, DL of (15.61 ± 1.9)%, mean diameter of (198 ± 4.7) nm. The release of paclitaxel and spirulina from the nanoparticle matrix at pH 6.2 was almost 45% and 80% in 5 h and 120 h, respectively. The oral bioavailability for the paclitaxel spirulina nanoparticles developed is 24.0% at 10 mg/kg paclitaxel dose, which is 10 times of that for oral pure paclitaxel. The results suggest that RSM-CCRD could efficiently be applied for the modeling of nanoparticles. The paclitaxel and spirulina release rate in the tumor cells may be higher than in normal cells. Paclitaxel spirulina nanoparticle formulation may have higher bioavailability and longer sustainable therapeutic time as compared with pure paclitaxel.

Conclusion:

Paclitaxel-Spirulina co-loaded nanoparticles could be effectively useful in gastric cancer as chemotherapeutic formulation.

Two-dimensional binary nanosheets (Bi2Te3@g-C3N4): Application toward the electrochemical detection of food toxic chemical

Bismuth telluride is considered as an efficient and super-active electrocatalyst in the sector of electrochemical application. Herein, we prepared binary nanosheets (Bi₂Te₃) through simple solvothermal and hydrothermal method. Furthermore, to enhance the electrocatalytic activity, graphitic carbon nitrides nanosheets (g-C₃N₄) were used to prepare the composition of Bi₂Te₃/g-C₃N₄ binary nanosheets (BNs) with help of hydrothermal energy. Moreover, Bi₂Te₃/g-C₃N₄ hybrid was characterized by various techniques (XRD, XPS, SEM, TEM, EDS and EIS analysis). The electrochemical performance of Bi₂Te₃/g-C₃N₄ BNs modified GCEs were analyzed by electrochemical technique (DPV, EIS and CV methods). As modified the Bi₂Te₃/g-C₃N₄ BNs modified electrode exhibits excellent electrochemical activity towards food toxic ractopamine (RAC) with high-sensitive and nano-molar detection limit (LOD). Besides, the practical ability was analyzed to detect the RAC in meat samples using Bi₂Te₃/g-C₃N₄ BNs modified GCE.

Synthesis of a hierarchical carbon fiber@cobalt ferrite@manganese dioxide composite and its application as a microwave absorber

In this study, a novel hierarchical carbon fiber@cobalt ferrite@manganese dioxide (CF@CoFe₂O₄@MnO₂) composite was facilely prepared via a sol–gel method and hydrothermal reaction. The morphology, structure, chemical and element composition, crystal form, elemental binding energy, magnetic behavior and microwave absorbing performance of the composite were carefully investigated. According to its hysteresis loops, the composite exhibits a typical soft magnetic behavior, with a M_s value of 30.2 emu g⁻¹. Besides, the as-synthesized CF@CoFe₂O₄@MnO₂ composite exhibits superior microwave absorption performance mainly due to reasonable electromagnetic matching, and its minimum reflection loss value can reach −34 dB with a sample thickness of just 1.5 mm. The composite can be regarded as an ideal microwave absorber.

In this study, a novel hierarchical carbon fiber@cobalt ferrite@manganese dioxide (CF@CoFe₂O₄@MnO₂) composite was facilely prepared via a sol–gel method and hydrothermal reaction.

Two-Step Solvothermal Synthesis of (Zn0.5Co0.5Fe2O4/Mn0.5Ni0.5Fe2O4)@C-MWCNTs Hybrid with Enhanced Low Frequency Microwave Absorbing Performance

In this study, the quaternary hybrid of (Zn0.5Co0.5Fe2O4/Mn0.5Ni0.5Fe2O4)@C-MWCNTs with high-performance in low frequency electromagnetic absorption was synthesized via a facile two-step solvothermal synthesis method. The physicochemical properties as well as electromagnetic parameters and microwave absorption performance were characterized by XRD, SEM, TEM, RS, TGA, and VNA, respectively. The results indicate a nuclear-shell morphology of this hybrid for amorphous carbon coated on the surface of Zn0.5Co0.5Fe2O4 and Mn0.5Ni0.5Fe2O4 mixed polycrystalline ferrites. In addition, the MWCNTs synchronously enwind in the nuclear-shell NPs to form a special cross-linking structure. The outstanding low frequency microwave absorption property is attributed to the synergistic effect of dielectric and magnetic loss, better impedance matching condition, and excellent attenuation characteristics of the as-prepared paramagnetic quaternary hybrid. Maximum RL of -35.14 dB at 0.56 GHz with an effective absorption bandwidth in the range of 0.27-1.01 GHz can be obtained with thickness of 5 mm. This hybrid exhibits superior low frequency microwave absorption properties compared with other ferrite-carbon nanocomposites. This investigation provides a new route to prepare suitable candidates for the absorption of electromagnetic waves in a low frequency band on account of its good performance and simple preparation process.

Facile synthesis of reduced graphene oxide-wrapped CNFs with controllable chemical reduction degree for enhanced microwave absorption performance

The rGO-wrapped nanocomposites can be regarded as promising candidates for the development of advanced microwave absorbing materials. In this work, hierarchical rGO-wrapped CNFs were prepared via a two-step strategy, including a classical modified Hummers method and a green reduction reaction. Accompany with the chemical treatments, graphene oxide appears on the outer walls of carbon nanofibers. By modulating the addition amount of ascorbic acid, the outer graphene oxide can be controllably reduced. Moreover, the CNFs/rGO with proper reduction degree exhibits desirable microwave absorption performance, whose minimum RL and effective bandwidth are -38.1 dB (3.85 GHz, d = 5.0 mm) and 4.1 GHz (5.08-9.18 GHz, d = 3.5 mm). The superior microwave attenuation performance is attributed to the synergistic effects between the CNFs and rGO. While the nanofibers provide the obtained sample with an extremely long conductive network, rGO introduces a moderate amount of lattice defects and functional groups, resulting in desirable conductivity loss and multiple polarizations. The existence of rGO also endows CNFs/rGO with suitable dielectric values so that the absorber achieves well impedance matching. Considering the excellent microwave absorption performance, this research provides a new facile route to fabricate rGO-wrapped carbonaceous materials with proper oxygen-containing groups for MAMs.

Rational Construction of Hierarchically Porous Fe-Co/N-Doped Carbon/rGO Composites for Broadband Microwave Absorption

Developing lightweight and broadband microwave absorbers for dealing with serious electromagnetic radiation pollution is a great challenge. Here, a novel Fe-Co/N-doped carbon/reduced graphene oxide (Fe-Co/NC/rGO) composite with hierarchically porous structure was designed and synthetized by in situ growth of Fe-doped Co-based metal organic frameworks (Co-MOF) on the sheets of porous cocoon-like rGO followed by calcination. The Fe-Co/NC composites are homogeneously distributed on the sheets of porous rGO. The Fe-Co/NC/rGO composite with multiple components (Fe/Co/NC/rGO) causes magnetic loss, dielectric loss, resistance loss, interfacial polarization, and good impedance matching. The hierarchically porous structure of the Fe-Co/NC/rGO enhances the multiple reflections and scattering of microwaves. Compared with the Co/NC and Fe-Co/NC, the hierarchically porous Fe-Co/NC/rGO composite exhibits much better microwave absorption performances due to the rational composition and porous structural design. Its minimum reflection loss (RLmin) reaches - 43.26 dB at 11.28 GHz with a thickness of 2.5 mm, and the effective absorption frequency (RL ≤ - 10 dB) is up to 9.12 GHz (8.88-18 GHz) with the same thickness of 2.5 mm. Moreover, the widest effective bandwidth of 9.29 GHz occurs at a thickness of 2.63 mm. This work provides a lightweight and broadband microwave absorbing material while offering a new idea to design excellent microwave absorbers with multicomponent and hierarchically porous structures.

Novel Microwave Absorber of Ni x Mn1-x Fe2O4/Carbonized Chaff (x = 0.3, 0.5, and 0.7) Based on Biomass

A novel magnetic nanocomposite of Ni x Mn1-x Fe2O4/carbonized chaff (x = 0.3, 0.5, and 0.7) has been synthesized successfully via the co-carbonization and hydrothermal method. The microstructure, morphology, complex permittivity and permeability, and microwave absorbing properties were systematically studied by X-ray diffraction, scanning electron microscopy, and a vector network analyzer. Compared to the pure Ni0.5Mn0.5Fe2O4 NPs, the Ni0.3Mn0.7Fe2O4/carbonized chaff-N2 composite exhibits an optimal microwave absorption property at 4 mm as the mass percent of carbonized chaff is 10 wt %, the maximum reflection loss of which can reach -14.58 dB at 1.91 GHz with the -10 dB frequency bandwidth in the range of 1.46-2.41 GHz (0.95 GHz). The enhanced electromagnetic wave absorbing performance is ascribed to the good synergistic effect among laminated structures, better impedance matching condition, strong natural resonance loss, Debye dipolar relaxation to some extent, and so forth. Most importantly, this study provides a novel way to prepare easily degradable, environment-friendly, and high-efficiency electromagnetic wave absorbers by utilizing the structural property of renewable biomaterials.

Preparation of SiO2-MnFe2O4 Composites via One-Pot Hydrothermal Synthesis Method and Microwave Absorption Investigation in S-Band

MnFe2O4 NPs are successfully decorated on the surface of SiO2 sheets to form the SiO2-MnFe2O4 composite via one-pot hydrothermal synthesis method. The phase identification, morphology, crystal structure, distribution of elements, and microwave absorbing properties in S-band (1.55~3.4 GHz) of the as-prepared composite were investigated by XRD, SEM, TEM, and Vector Network Analyzer (VNA) respectively. Compared with the pure MnFe2O4 NPs, the as-prepared SiO2-MnFe2O4 composite exhibits enhanced microwave absorption performance in this frequency band due to the strong eddy current loss, better impedance matching, excellent attenuation characteristic, and multiple Debye relaxation processes. The maximum reflection loss of -14.87 dB at 2.25 GHz with a broader -10 dB bandwidth over the frequency range of 1.67~2.9 GHz (1.23 GHz) can be obtained at the thickness of 4 mm. Most importantly, the preparation method used here is relatively simple, hence such composite can be served as a potential candidate for effective microwave absorption in S-band.

Synthesis of Single-Component Metal Oxides with Controllable Multi-Shelled Structure and their Morphology-Related Applications

Multi-shelled hollow spheres metal oxides, namely materials with more than three shells, have attracted increasing attention due to their unique structure. The preparation methods of typical metal oxides including NiO, Co₃ O₄ and ZnO etc. have been summarized in this review. Simultaneously, the parameters that influence the ultimate morphologies, shell number as well as the compositions have also been discussed. The potential application fields in energy conversion and storage, electromagnetic wave absorption, photocatalysis that related to the unique structure are also highlighted. Finally, the future researches of multi-shelled hollow spheres metal oxides are further discussed.

Ultralight Cellular Foam from Cellulose Nanofiber/Carbon Nanotube Self-Assemblies for Ultrabroad-Band Microwave Absorption

Microwave absorption materials (MAMs) with lightweight density and ultrabroad-band microwave absorption performance are urgently needed in advanced MAMs, which are still a big challenge and have been rarely achieved. Here, a new wide bandwidth absorption model was designed, which fuses the electromagnetic resonance loss ability of a periodic porous structure in the low-frequency range and the dielectric loss ability of dielectric materials in the high-frequency range. Based on this model, a lightweight porous cellulose nanofiber (CNF)/carbon nanotube (CNT) foam consisting of a cellular vertical porous architecture with the macropore diameters between 30 and 90 μm and a nanoporous architecture at a scale of 1.7-50 nm was obtained by an ice-template method using CNTs and CNFs as "building blocks". Benefiting from the unique architecture, the effective absorption bandwidth reaches 29.7 GHz, and its specific microwave absorption performance exceeds 80,000 dB·cm^-2·g^-1, which far surpasses those of the MAMs previously reported, including all CNT-based composites. Moreover, the CNF/CNT foam possesses ultralow density (9.2 mg/cm³) and strong fatigue resistance, all coming from the well-interconnected porous structure and the strong hydrogen bonds among CNF-CNF and CNF-CNT molecular chains.

A facile coprecipitation method to synthesize FexOy/Fe decorated graphite sheets with enhanced microwave absorption properties

Fe_xO_y/Fe decorated graphite sheets (DGS) are synthesized using a facile coprecipitation method followed by heat treatment under different conditions. The size and chemical composition of the particles loaded on graphite sheets can be tailored by adjusting the heat treatment temperature and atmosphere. The obtained α-Fe₂O₃ DGS (S₁), Fe₃O₄ DGS (S₂ and S₃), and Fe DGS (S₄) all exhibit excellent electromagnetic (EM) wave absorption when compared with conventional graphite/magnetic-particle composites. The minimum reflection loss (RL) can reach -42.1 dB at 4.16 GHz in the S₂/paraffin composites. The bandwidth of the RL below -10 dB covers 4.4 GHz (11.04-15.44 GHz) with a thickness of 2 mm. A possible EM wave loss mechanism has been proposed in detail. The multiple absorbing mechanisms could control the excellent absorption, resulting in a product with a feasible application in stealth materials.

High-Temperature Oxidation-Resistant ZrN0.4B0.6/SiC Nanohybrid for Enhanced Microwave Absorption

Most microwave absorbers lose their function under harsh working conditions, such as a high temperature and an oxidative environment. Here, we developed a heterogeneous ZrN_0.4B_0.6/SiC nanohybrid via combined catalytic chemical vapor deposition (CCVD) and chemical vapor infiltration (CVI) processes using ZrB₂ as the starting material. The composition and structure of the ZrN_0.4B_0.6/SiC nanohybrid were controlled by tuning the CCVD and CVI parameters, such as reaction temperature, time, and reactant concentration. The optimal heterogeneous ZrN_0.4B_0.6/SiC nanohybrids were obtained initially by preparing ZrB₂@C via the CCVD process at 650 °C for 30 min and the subsequent CVI at 1500 °C, where the ZrB₂@C reacted with Si under N₂. The ZrN_0.4B_0.6/SiC nanohybrid exhibited enhanced microwave absorption ability with a minimum reflection loss value of approximately -50.8 dB at 7.7 GHz, a thickness of ∼3.05 mm, and antioxidation features at a high temperature of 600 °C. The heterogeneous ZrN_0.4B_0.6/SiC nanohybrid possessed reasonable conductivity, leading to dielectric loss, whereas SiC nanofibers formed a three-dimensional network that brought higher dipole moments, whereas a small part of the ZrN_0.4B_0.6/SiC nanohybrid structure generated an effective interface for higher attenuation of microwaves. Therefore, these material features synergistically resulted in a well-defined Debye relaxation, Maxwell-Wagner relaxation, dipole polarization, and the quarter-wavelength cancellation, which accounted for the enhanced microwave absorption.

Lightweight Ti2CT x MXene/Poly(vinyl alcohol) Composite Foams for Electromagnetic Wave Shielding with Absorption-Dominated Feature

Lightweight absorption-dominated electromagnetic interference (EMI) shielding materials are more attractive than conventional reflection-dominated counterparts because they minimize the twice pollution of the reflected electromagnetic (EM) wave. Here, porous Ti₂CT _x MXene/poly(vinyl alcohol) composite foams constructed by few-layered Ti₂CT _x (f-Ti₂CT _x) MXene and poly(vinyl alcohol) (PVA) are fabricated via a facile freeze-drying method. As superior EMI shielding materials, their calculated specific shielding effectiveness reaches up to 5136 dB cm² g^-1 with an ultralow filler content of only 0.15 vol % and reflection effectiveness (SE_R) of less than 2 dB, representing the excellent absorption-dominated shielding performance. Contrast experiment reveals that the good impedance matching derived from the multiple porous structures, internal reflection, and polarization effect (dipole and interfacial polarization) plays a synergistic role in the improved absorption efficiency and superior EMI shielding performance. Consequently, this work provides a promising MXene-based EMI shielding candidate with lightweight and high strength features.

Vacuum Casting and Mechanical Characterization of Nanocomposites from Epoxy and Oxidized Multi-Walled Carbon Nanotubes

Sample preparation is an important step when testing the mechanical properties of materials. Especially, when carbon nanotubes (CNT) are added to epoxy resin, the increase in viscosity complicates the casting of testing specimens. We present a vacuum casting approach for different geometries in order to produce specimens from functional nanocomposites that consist of epoxy matrix and oxidized multi-walled carbon nanotubes (MWCNTs). The nanocomposites were characterized with various mechanical tests that showed improved fracture toughness, bending and tensile properties performance by addition of oxidized MWCNTs. Strengthening mechanisms were analyzed by SEM images of fracture surfaces and in-situ imaging by digital image correlation (DIC).

Distinct plasmon resonance enhanced microwave absorption of strawberry-like Co/C/Fe/C core–shell hierarchical flowers via engineering the diameter and interparticle spacing of Fe/C nanoparticles

Strawberry-like Co/C/Fe/C core–shell hierarchical flowers (CSHFs) consisting of separated Fe/C nanoparticles (NPs) anchoring on a Co HF surface were prepared by decomposing Fe(CO)₅ in the presence of Co HFs. Changing the decomposition temperature (T_d) and Fe(CO)₅ volume (δ) could also facilely modulate the phase structure, surface morphology and composition of the products. The low T_d and small δ helped form Co/C/Fe/C CSHFs with a strawberry-like plasmon surface. The diameter and interparticle spacing-dependent electromagnetic properties were investigated at 2–18 GHz. The interparticle-spacing-to-diameter ratio determines the plasmon resonance and coupling. The permittivity and permeability enhanced by strong plasmon resonance were exhibited by Co/C/Fe/C CSHFs formed at δ = 3–4 mL with the interparticle-spacing-to-diameter ratio of 1.36–0.76. The collective oscillation of the conduction band electrons and near field on the Co/C and Fe/C surfaces generated a surface plasmon resonance and coupling, which were responsible for significantly enhanced permittivity and permeability with negative values. In view of the synergistic effect of the enhanced permittivity and permeability, dual dielectric relaxations, dual magnetic resonances, high attenuation and good impedance matching, Co/C/Fe/C CSHFs with particle size of 110 ± 20–380 ± 100 nm and interparticle spacing of 150 ± 50 nm were excellent absorbers that feature strong absorption, broad bandwidth and light weight. An optimal reflection loss (R_L) of −45.06 was found at 17.92 GHz for an absorber thickness of 1.6 mm, and the frequency range (R_L ≤ −20 dB, 99% absorption) was over 2–18 GHz. Our findings demonstrated that optimally designed plasmonic heterostructures must be fabricated to improve microwave absorption performances for future applications.

Plasmon resonance enhanced permittivity, permeability, and microwave absorption were found in Fe/C nanoparticles anchoring on Co/C hierarchical flowers synthesized through a carefully devised kinetically tuned procedure.

Sustainable fixation of CO2 into epoxides to form cyclic carbonates using hollow marigold CuCo2O4 spinel microspheres as a robust catalyst

The present work demonstrates the chemical fixation of CO₂ for the synthesis of organic carbonates using mesoporous hollow marigold CuCo₂O₄ spinel microspheres as a catalyst prepared using the solvothermal method.

Edge-oriented MoS2 supported on nickel/carbon core–shell nanospheres for enhanced hydrogen evolution reaction performance

Edge-oriented molybdenum disulfide, growing on the surface of carbon shell with a nickel core, exhibits the enhanced performance on hydrogen evolution reaction.