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Magnetic Fe3O4/MnO2/TiO2/polypyrrole (PPy) heterostructure as adsorbent for adsorbing Mn7+ was synthesized by combining hydrothermal method and chemical oxidation method. The heterostructure was characterized by field‐emission scanning electron microscope, Fourier transform infrared spectroscopy, X‐ray diffraction, and vibrating sample magnetometer. Its saturation magnetization is 18.88 emu/g, so it is easy to separate it from the solution. The feasibility of Fe3O4/MnO2/TiO2/PPy heterostructure to remove Mn7+ was researched in detail. It is found that the optimal pH is 2. The initial adsorption rate can reach 4.60 mg/g min. At 288.15 K, the maximum equilibrium adsorption capacity is 202.8 mg/g. Adsorption kinetics follows a pseudo second order model, as well as is determined by through membrane diffusion processes. The Langmuir isotherm model is used to describe the adsorption isotherm behavior. Besides, thermodynamic parameters indicate spontaneous adsorption behavior, and entropy of the endothermic reaction increases. Finally, the cycle test results show that the adsorbent has better cycle performance, displaying broad application prospects. [ABSTRACT FROM AUTHOR]

[Display omitted] Increasing electromagnetic (EM) radiation has driven the rapid development of carbon-based EM wave absorption materials, but the design of light-weight and efficient carbon-based materials remains a huge challenge. Herein, N -doped carbon fibers embedded with CoNi alloy particles (CoNi/C fibers) were synthesized via electrospinning technology and carbonization. Then, conductive polypyrrole-coated CoNi/C fibers (CoNi/C@PPy composites) were synthesized by chemical polymerization. As-synthesized CoNi/C@PPy composites showed outstanding EM wave absorption property due to the synergistic effect between CoNi, N -doped carbon fibers and PPy. The optimal reflection loss (RL) is -68.78 dB (12.90 GHz) with the thickness of 2.43 mm and the low filler loading of 15 wt%. The widest effective absorption bandwidth (EAB) is 5.62 GHz with the thickness of 2.10 mm and the low filler loading of 20 wt%. The outstanding EM wave absorption property is mainly attributed to 3D network structure, great impedance matching and strong dielectric loss. The results showed that embedding magnetic alloy particles in carbon fibers coated with conductive polymers is an effective strategy for constructing efficient lightweight EM wave absorption materials. [ABSTRACT FROM AUTHOR]

[Display omitted] The conductive networks for electron hopping and migration constructed by one-dimensional (1D) composite absorbers are highly desirable to improve the electromagnetic (EM) wave attenuation capacity. Herein, the Ni@Co/C@polypyrrole (PPy) composites integrating the advantages of component and microstructure were fabricated. The addition of Co/C and PPy effectively optimized the impedance matching and improved the EM attenuation. Under the comprehensive impacts of multiple reflections/scattering, conduction loss and interface polarization, the Ni@Co/C@PPy composites showed superior EM wave absorption with the reflection loss (RL) value of −48.76 dB and the effective absorption bandwidth (EAB) of 5.10 GHz at a corresponding thickness of 2.0 mm. The largest EAB could reach 5.54 GHz (7.24–12.78 GHz) at the thickness of 2.2 mm. This work provides a great reference for fabricating 1D novel EM wave absorption materials. [ABSTRACT FROM AUTHOR]

[Display omitted] Nowadays, ferrites/carbon fibers have attracted considerable attention as microwave absorption materials (MA) due to the synergistic effect between dielectric and magnetic loss. Herein, the ZnFe 2 O 4 /C fibers were fabricated via electrospinning and calcination methods, and then polypyrrole (PPy) successfully coated on the fibers via oxidative polymerization. The ZnFe 2 O 4 /C@PPy composites exhibit enhanced EM wave absorption performance with the loading of 25 wt%. The optimal reflection loss (RL) value is up to −66.34 dB (13.80 GHz) and effective absorption bandwidth (EAB) is 5.74 GHz (11.78–17.52 GHz) with a matching thickness of 1.93 mm. Besides, high-efficient absorption performance of the ZnFe 2 O 4 /C@PPy composites is mainly attributed to the dielectric loss and ideal impedance matching. This study reveals a novel approach to development of ferrites/carbon fibers coated with PPy, and the ZnFe 2 O 4 /C@PPy composites exhibit great potential application as the materials with high-efficient absorption properties. [ABSTRACT FROM AUTHOR]

[Display omitted] Metal-organic framework (MOF) materials have caused widespread concerns in the field of microwave absorption, due to the unique microstructure and electronic state. Herein, the CoZn/C@MoS 2 @polypyrrole (PPy) composites were prepared through MOF self-template method. The MoS 2 sheets and PPy shell incorporated for optimizing impedance matching of two-dimensional (2D) CoZn/C composites. The introduction of MoS 2 sheets and PPy shell endowed the composites with enhanced microwave absorption. The as-prepared CoZn/C@MoS 2 @PPy composites showed a minimum reflection loss (RL) of −49.18 dB with the thickness of 1.5 mm. In addition, the effective absorption bandwidth (EAB, RL values exceeding −10 dB) covered 4.56 GHz, which showed greater performances than CoZn/C composites under a lower thickness (<2 mm). This work not only provides a facile route for fabricating MOF-derived carbon-based composites as microwave absorbers, but also broadens the application of MOF materials. [ABSTRACT FROM AUTHOR]

NiCo-HFPR-0.2 composite is prepared for high-performance electromagnetic wave absorption, exhibiting the RL min of −61.20 dB at 14.26 GHz and 1.56 mm, the EAB of 4.90 GHz at 1.57 mm, and the reduction in RCS up to 31.0 dB m2 at θ=0°. [Display omitted] • NiCo-HFPR-0.2 composite is successfully fabricated for electromagnetic wave absorption. • The composite has the RL min of −61.20 dB at 14.26 GHz and 1.56 mm and the EAB of 4.90 GHz at 1.57 mm. • These performances are attributed to the multiple losses and impedance match stemming from reasonable structural design. • At θ = 0° and Phi = 0°, the coating of this composite reduces the RCS value by 31.0 dB m2 compared to the sole PEC layer. In contemporary times, electromagnetic radiation poses a significant threat to both human health and the normal functioning of electronic devices. Developing composites as adsorption materials possess exceptional electromagnetic wave absorption performances can efficient address this critical issue. Herein, hollow core–shell NiCo 2 O 4 @polypyrrole nanofibers/reduced graphene oxide (NiCo-HFPR) composites are fabricated by the combination of electrostatic spinning, air calcination, in-situ polymerization, freeze-drying and hydrazine vapor reduction. As anticipated, NiCo-HFPR-0.2 exhibits noteworthy properties, with the minimum reflection loss (RL min) of −61.20 dB at 14.26 GHz and 1.56 mm, as well as the effective absorption bandwidth (EAB) of 4.90 GHz at 1.57 mm. Additionally, the simulation procedure is employed to determine the radar cross-section (RCS) attenuation. In comparison to a singular perfect electrically conductive (PEC) layer, the PEC layer coated with NiCo-HFPR-0.2 consistently yields an RCS value below −10 dB m2 within the range of −60° < θ < 60°. The RCS attenuation value of the NiCo-HFPR-0.2 coating achieves an outstanding 31.0 dB m2 at θ = 0°, strongly affirming the ability to effectively attenuate electromagnetic wave in real-world applications. The employed experimental methodology, the meticulously crafted composite, and the simulation outcomes presented in this study bear great promise for the progressive advancement of both theoretical investigations and practical applications within the domain of electromagnetic wave absorption. [ABSTRACT FROM AUTHOR]

In here, cobalt-zinc bimetallic oxides@polypyrrole (PPy) composites with core–shell structure are prepared, and the prepared Co 3 O 4 /ZnCo 2 O 4 @PPy (CZCP) has a wide absorption of 5.58 GHz, while ZnCo 2 O 4 /ZnO@PPy (ZCZP) has a strong reflection loss of −71.2 dB. [Display omitted] • By changing the ratio of Co2+ and Zn2+ of the MOF precursors, the various cobalt-zinc bimetallic oxides are fabricated. • Cobalt-zinc bimetallic oxides@polypyrrole (PPy) composites with core–shell structure are prepared through in situ polymerization method. • When the loading is 50 wt%, the EAB of Co 3 O 4 /ZnCo 2 O 4 @PPy is 5.58 GHz (12.42–18 GHz) at 1.53 mm, and the RL min of ZnCo 2 O 4 /ZnO@PPy is −71.2 dB at 13.04 GHz and 1.84 mm. Composite materials that combine magnetic and dielectric losses offer a potential solution to enhance impedance match and significantly improve microwave absorption. In this study, Co 3 O 4 /ZnCo 2 O 4 and ZnCo 2 O 4 /ZnO with varying metal oxide compositions are successfully synthesized, which are achieved by modifying the ratios of Co2+ and Zn2+ ions in the CoZn bimetallic metal–organic framework (MOF) precursor, followed by a high-temperature oxidative calcination process. Subsequently, a layer of polypyrrole (PPy) is coated onto the composite surfaces, resulting in the formation of core–shell structures known as Co 3 O 4 /ZnCo 2 O 4 @PPy (CZCP) and ZnCo 2 O 4 /ZnO@PPy (ZCZP) composites. The proposed method allows for rapid adjustments to the metal oxide composition within the inner shell, enabling the creation of composites with varying degrees of magnetic losses. The inclusion of PPy in the outer shell serves to enhance the bonding strength of the entire composite structure while contributing to conductive and dielectric losses. In specific experimental conditions, when the loading is set at 50 wt%, the CZCP composite exhibits an effective absorption bandwidth (EAB) of 5.58 GHz (12.42 GHz-18 GHz) at a thickness of 1.53 mm. Meanwhile, the ZCZP composite demonstrates an impressive minimum reflection loss (RL min) of −71.2 dB at 13.04 GHz, with a thickness of 1.84 mm. This study offers a synthesis strategy for designing absorbent composites that possess light weight and excellent absorptive properties, thereby contributing to the advancement of electromagnetic wave absorbing materials. [ABSTRACT FROM AUTHOR]

Ni NCs@Z-P/RGO composites are prepared for high-performance electromagnetic wave absorption, exhibiting RL min of −63.58 dB at 14.3 GHz with a thickness 1.61 mm, the EAB of 5.08 GHz (11.92 GHz-17 GHz) at a thickness of 1.67 mm, and the reduction in RCS up to 26.6 dB m2 at θ=0°. [Display omitted] • One-dimensional Ni nanochains@Zn2+ doping PPy/reduced graphene oxide composites for electromagnetic wave absorption are fabricated. • The composite has the RL min of −63.58 dB at 14.3 GHz with a thickness 1.61 mm and the EAB of 5.08 GHz (11.92 GHz-17 GHz) at a thickness of 1.67 mm. • At θ = 0° and PHi = 0°, the coating of this material reduces the RCS value by 26.6 dB m2 compared to the uncoated perfectly conducting layer. Nowadays, electromagnetic radiation significantly impacts the normal operation of electronic devices and poses risks to human health. To effectively address this problem, the development of composites that exhibit exceptional electrochemical wave absorption through the combination of different components holds great promise. In this study, we have successfully prepared 1D Ni nanochains@Zn2+ doping polypyrrole/reduced graphene oxide (Ni NCs@Z-P/RGO, denoted as R-x) composites using a combination of hydrothermal, solvothermal, in situ polymerization, and physical blending methods. Notably, the R-2 composite demonstrates a remarkable minimum reflection loss (RL min) of −63.58 dB at 14.3 GHz, with a thickness of 1.61 mm. Furthermore, the R-2 composite exhibits an impressive effective absorption bandwidth (EAB) of 5.08 GHz (11.92 GHz-17 GHz) at a thickness of 1.67 mm. These outstanding performances can be attributed to the synergistic effect of the different components and a well-thought-out structural design. Moreover, to showcase the practical applicability of the material, we have conducted additional investigations on the reduction of the radar cross-sectional area (RCS). The results strongly demonstrate that the prepared composite material, when used as a coating, effectively reduces the RCS value by up to 26.6 dB m2 for R-2 at θ = 0°. The experimental methods and simulations presented in this study hold significant potential for application in wave absorption research and practical implementations. Additionally, the prepared Ni NCs@Z-P/RGO composites demonstrate feasibility as wave-absorbing materials for future utilization. [ABSTRACT FROM AUTHOR]

Fe 3 O 4 @PPy/rGO composites have been fabricated by hydrothermal method, in situ polymerization method, directional freeze-drying and hydrazine vapor reduction, exhibiting the RL min of −61.20 dB at 1.89 mm and the EAB of 5.26 GHz at 1.71 mm. [Display omitted] • Fe 3 O 4 @PPy/rGO (FPG) composites have been fabricated by hydrothermal method, in situ polymerization method, directional freeze-drying and hydrazine vapor reduction. • The enhanced EMW adsorption performances are attributed to the synergy effect of multiple EMW losses stemming from Fe 3 O 4 , PPy, rGO and optimized impedance match. • FPG-4 exhibits the RL min of −61.20 dB at 1.89 mm and the EAB of 5.26 GHz at 1.71 mm. The design of heterostructures with reasonable chemical composition and spatial structure is one of the effective strategies to achieve high performances electromagnetic wave (EMW) absorption. Herein, reduced graphene oxide (rGO) nanosheets decorated with hollow core–shell Fe 3 O 4 @PPy (FP) microspheres have been prepared by the combination of hydrothermal method, in situ polymerization method, directional freeze-drying and hydrazine vapor reduction. FP acting as traps can consume EMW trapped into their interior through the magnetic and dielectric losses. RGO nanosheets forming the conductive network are served as multi-reflected layers. Moreover, the impedance matching is optimized by the synergistic effect between FP and rGO. As expected, the synthetic Fe 3 O 4 @PPy/rGO (FPG) composite shows excellent EMW absorption performances with the minimum reflect loss (RL min) of −61.20 dB at 1.89 mm and the effective absorption bandwidth (EAB) of 5.26 GHz at 1.71 mm. The excellent performances for the heterostructure are attributed to the synergistic effect of conductive loss, dielectric loss, magnetic loss, multiple reflection loss, and optimized impedance matching. This work provides a simple and effective strategy for the fabrication of lightweight, thin and high-performances EMW absorbing materials. [ABSTRACT FROM AUTHOR]

CuS/Fe 3 O 4 @polypyrrole composites are successfully prepared via combining hydrothermal method, solvothermal method and in-situ polymerization method, exhibiting the RL min of −74.12 dB at 2.96 mm and the EAB of 4.6 GHz at 1.68 mm. [Display omitted] • CuS/Fe 3 O 4 @PPy composites are successfully fabricated by combining hydrothermal method, solvothermal method and in-situ polymerization method. • The enhanced electromagnetic loss and the optimized impedance matching are attributed to the synergy effect of CuS, Fe 3 O 4 and PPy. • The RL min of CuS/Fe 3 O 4 @PPy composites is −74.12 dB at 6.82 GHz with the thickness of 2.96 mm. Recently, electromagnetic radiation is a serious threat to equipment accuracy, military safety and human health. The combination with different materials to fabricate absorber composites with well-designed morphology is expected to ameliorate this issue. In here, CuS/Fe 3 O 4 @polypyrrole (CuS/Fe 3 O 4 @PPy) flower-like composites are constructed by the combination of hydrothermal method, solvothermal method and in-situ polymerization. CuS with flower-like structure consisting of nanosheets can provide a conductive backbone and large specific surface area. Hollow Fe 3 O 4 microspheres play a key role in deciding magnetic loss, and electromagnetic waves can penetrate their hollow structure, result in multiple reflection and refraction. PPy coating can enhance the combined strength of composite, and effectively consume microwaves by scattering and multiple refraction in the intercalated structure. As expected, the minimum reflection loss (RL min) of CuS/Fe 3 O 4 @PPy composites is −74.12 dB at 8.16 GHz with a thickness of 2.96 mm, and the effective absorption bandwidth (EAB) is 4.6 GHz (13.4–18.0 GHz) at 1.68 mm. The excellent electromagnetic wave absorption performances are attributed to the synergy effect of different components. This work provides a unique strategy for the structural design of flower-like microspheres in the field of electromagnetic wave absorption. [ABSTRACT FROM AUTHOR]

• Fe 3 O 4 @PPy-AP composite is synthesized for rapid Mn (VII) adsorption from solution. • The maximum adsorption capacity of the composite is 781.25 mg g-1 at 318.15 K. • Both the N atoms in PPy and AP can adsorb Mn (VII) through coordination effect. 2-aminopyridine functionalized magnetic core–shell Fe 3 O 4 @polypyrrole structure (Fe 3 O 4 @PPy-AP composite) is fabricated to remove Mn (VII) from water. The adsorbent fully combines the easy magnetic separation of Fe 3 O 4 microspheres, the excellent corrosion resistance of PPy, as well as double-layer adsorption for Mn (VII) of PPy and AP. The effects of time, temperature and pH on the adsorption performances and adsorption mechanism are investigated in detail, for which the significance of structure of Fe 3 O 4 @PPy-AP composite is elucidated. It is clear that the adsorption process is chemical adsorption. The adsorption kinetics and isotherm is more suitable for pseudo-second order model and Freundlich model. The initial adsorption rate is 67.43 min g mg−1, and the maximum adsorption capacity can reach 781.25 mg g−1 at 318.15 K. The film diffusion dominates the speed of the entire adsorption process. Adsorption thermodynamic calculations show that ΔS and ΔH are 198.33 J mol−1 K−1 and 37.88 kJ mol−1, respectively, and the decreased ΔG with increasing temperature indicates that the adsorption process is endothermic and spontaneous. The Fe 3 O 4 @PPy-AP composite only loses less than 1% of Mn (VII) adsorption capacity after each adsorption–desorption cycle. This Fe 3 O 4 @PPy-AP composite with good magnetic properties and dual adsorption properties has broad application prospects in the rapid separation and adsorption of heavy metal ions. [ABSTRACT FROM AUTHOR]