CuxCo1-xFe2O4 (x = 0.33, 0.67, 1) Spinel Ferrite Nanoparticles Based Thermoplastic Polyurethane Nanocomposites with Reduced Graphene Oxide for Highly Efficient Electromagnetic Interference Shielding

Cu_xCo_1-xFe₂O₄ (x = 0.33, 0.67, 1)-reduced graphene oxide (rGO)-thermoplastic polyurethane (TPU) nanocomposites exhibiting highly efficient electromagnetic interference (EMI) shielding were prepared by a melt-mixing approach using a microcompounder. Spinel ferrite Cu_0.33Co_0.67Fe₂O₄ (CuCoF1), Cu_0.67Co_0.33Fe₂O₄ (CuCoF2) and CuFe₂O₄ (CuF3) nanoparticles were synthesized using the sonochemical method. The CuCoF1 and CuCoF2 exhibited typical ferromagnetic features, whereas CuF3 displayed superparamagnetic characteristics. The maximum value of EMI total shielding effectiveness (SE_T) was noticed to be 42.9 dB, 46.2 dB, and 58.8 dB for CuCoF1-rGO-TPU, CuCoF2-rGO-TPU, and CuF3-rGO-TPU nanocomposites, respectively, at a thickness of 1 mm. The highly efficient EMI shielding performance was attributed to the good impedance matching, conductive, dielectric, and magnetic loss. The demonstrated nanocomposites are promising candidates for a lightweight, flexible, and highly efficient EMI shielding material.     

Achieving ultra-high electromagnetic wave absorption by anchoring Co0.33Ni0.33Mn0.33Fe2O4 nanoparticles on graphene sheets using microwave-assisted polyol method

The Co_0.33Ni_0.33Mn_0.33Fe₂O₄/graphene nanocomposite for electromagnetic wave absorption was successfully synthesized from metal chlorides solutions and graphite powder by a simple and rapid microwave-assisted polyol method via anchoring the Co_0.33Ni_0.33Mn_0.33Fe₂O₄ nanoparticles on the layered graphene sheets. The Fe³⁺, Co²⁺, Ni²⁺ and Mn²⁺ ions in the solutions were attracted by graphene oxide obtained from graphite and converted to the precursors Fe(OH)₃, Co(OH)₂, Ni(OH)₂, and Mn(OH)₂ under slightly alkaline conditions. After the transformations of the precursors to Co-Ni-Mn ferrites and conversion of graphene oxide to graphene under microwave irradiation at 170?°C in just 25?min, the Co_0.33Ni_0.33Mn_0.33Fe₂O₄/graphene nanocomposite was prepared. The composition and structure of the nanocomposite were characterized by X-ray diffraction (XRD), inductive coupled plasma emission spectroscopy (ICP), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy (RS), transmission electron microscopy (TEM), etc. It was found that with the filling ratio of only 20?wt% and the thickness of 2.3?mm, the nanocomposite showed an ultra-wide effective absorption bandwidth (less than ?10?dB) of 8.48?GHz (from 9.52 to 18.00?GHz) with the minimum reflection loss of ??24.29?dB. Compared to pure graphene sheets, Co_0.33Ni_0.33Mn_0.33Fe₂O₄ nanoparticles and the counterparts reported in literature, the nanocomposite exhibited much better electromagnetic wave absorption, mainly attributed to strong wave attenuation, as a result of synergistic effects of dielectric loss, conductive loss and magnetic loss, and to good impedance matching. In view of its thin thickness, light weight and outstanding electromagnetic wave absorption property, the nanocomposite could be used as a very promising electromagnetic wave absorber.     

One-step hydrothermal synthesis and enhanced microwave absorption properties of Ni0.5Co0.5Fe2O4/graphene composites in low frequency band

Ni_0.5Co_0.5Fe₂O₄/graphene composites were synthesized successfully via one-step hydrothermal method. The crystal structure, morphology and corresponding elemental distribution, electromagnetic parameters and microwave absorption performances of the as-prepared composites were measured by XRD, SEM, TEM and VNA, respectively. The results indicated that the microwave absorbing performance can be obviously enhanced through the addition of graphene in a suitable range, the magnetic loss plays a dominant contribution for the microwave absorption of composites. The maximum reflection loss of ?30.92?dB at 0.84?GHz with a ?10?dB bandwidth over the frequency range of 0.58–1.19?GHz is obtained when the composite contains 12?wt% graphene and the thickness of sample is 4?mm. This investigation presents a simple method to prepare Ni_0.5Co_0.5Fe₂O₄/graphene composites with excellent microwave absorption performance in the low frequency band of 0.1–3?GHz.     

Graphene anchored Ce doped spinel ferrites for practical and technological applications

Graphene plays a remarkable role as a supporting material for the fabrication of a variety of nanocomposites. This work presents the fabrication of graphene-based Ce doped Ni–Co (Ni_0.5Co_0.5Ce_0.2Fe_1.8O₄/G) ferrite nanocomposites. Ni_0.5Co_0.5Fe₂O₄ and Ni_0.5Co_0.5Ce_0.2Fe_1.8O₄ were prepared using sol gel method. However, Ce doped Ni–Co spinel nanoferrite was chemically anchored on the surface of graphene. Different characterizations techniques were adopted to investigate the variations in the properties of ferrite composite due to the incorporation of graphene. Thermal analysis revealed 18% heat weight loss of Ce doped Ni–Co ferrite sample during treatment up to 1000 °C respectively. X-ray diffraction analysis depicted the presence of spinel phase structure of all synthesized nanocomposites. Fourier transform infrared analysis revealed two absorption bands of tetrahedral and octahedral sites of the spinel phase and presence of graphene contents in the Ni_0.8Ce_0.2CoFeO₄/G composite. FESEM images revealed an increased agglomeration due to the presence of graphene in the Ce doped Ni–Co ferrite composites. Graphene based Ce doped Ni–Co ferrite nanocomposite showed highest conductivity (4.52 mS/cm) than other ferrite composites. Magnetic characteristics showed an improvement in the Ni–Co ferrite sample by the substitutions of Ce³⁺ ions and graphene contents. The improvement in the properties of these nanocomposites makes them potential material for many applications such as fabrication of electrodes, energy storage and nanoelectronics devices.     

The Cobalt Zinc Spinel Ferrite Nanofiber: Lightweight and Efficient Microwave Absorber

To solve the heavy mass problem of the traditional spinel ferrite using as the microwave absorber, the Co_xZn_(1?x)Fe₂O₄ (x = 0.2, 0.4, 0.6, 0.8) ferrite nanofibres were synthesized by electrospinning method. The phase composition, morphology, and electromagnetic properties were analyzed. The results showed that all the as‐prepared Co_xZn_(1?x)Fe₂O₄ ferrites exhibited the homogeneous nanofibrous shape. The saturation magnetization and coercivity were enhanced by tuning the Co²⁺ content. The electromagnetic loss analysis indicated that the Co_0.6Zn_0.4Fe₂O₄ ferrite nanofiber performed the strongest microwave attenuation ability. The microwave absorbing coating containing 15 wt% of Co_0.6Zn_0.4Fe₂O₄ ferrite nanofiber showed the reflection loss less than ?10 dB in the whole X‐band and 80% of the Ku‐band frequencies. Meanwhile, the surface density was only 2.4 Kg/m².     

Copper substituted nickel ferrite nanoparticles anchored onto the graphene sheets as electrode materials for supercapacitors fabrication

Nickel ferrites with high theoretical capacitance value as compared to the other metal oxides have been applied as electrode material for energy storage devices i.e. batteries and supercapacitors. High tendency towards aggregation and less specific surface area make the metal oxides poor candidate for electrochemical applications. Therefore, the improvements in the electrochemical properties of nickel ferrites (NiFe₂O₄) are required. Here, we report the synthesis of graphene nano-sheets decorated with spherical copper substituted nickel ferrite nanoparticles for supercapacitors electrode fabrication. The copper substituted and unsubstituted NiFe₂O₄ nanoparticles were prepared via wet chemical co-precipitation route. Reduced graphene oxide (rGO) was prepared via well-known Hummer's method. After structural characterization of both ferrite (Ni_1-xCu_xFe₂O₄) nanoparticles and rGO, the ferrite particles were decorated onto the graphene sheets to obtain Ni_1-xCu_xFe₂O₄@rGO nanocomposites. The confirmation of preparation of these nanocomposites was confirmed by scanning electron microscopy (SEM). The electrochemical measurements of nanoparticles and their nanocomposites (Ni_0.9Cu_0.1Fe₂O₄@rGO) confirmed that the nanocomposites due to highly conductive nature and relatively high surface area showed better capacitive behavior as compared to bare nanoparticles. This enhanced electrochemical energy storage properties of nanocomposites were attributed to the graphene and also supported by electrical (I-V) measurements. The cyclic stability experiments results showed ~65% capacitance retention after 1000 cycles. However this retention was enhanced from 65% to 75% for the copper substituted nanoparticles (Ni_0.9Cu_0.1Fe₂O₄) and 65–85% for graphene based composites. All this data suggest that these nanoparticles and their composites can be utilized for supercapacitors electrodes fabrication.     

Synthesis and characterizations of Ni0.8Zn0.2Fe2O4-MWCNTs composites for their application in sea bed logging

Sea bed logging is new technique for the detection of hydrocarbon reservoir. Magnitude of EM waves is important for the detection of deep target hydrocarbon reservoir below 4000 m from the sea floor. A new aluminium based EM transmitter is developed and NiZn (Ni_0.8Zn_0.2Fe₂O₄) ferrite with and with out multiwall carbon nano tubes (MWCNTs) polymer composites as magnetic feeders are used in a scaled tank. Nickel zinc ferrite plays an important role in many applications due to its best magnetic properties. Nanocrystalline NiZn (Ni_0.8Zn_0.2Fe₂O₄) ferrite and novel Ni_0.8Zn_0.2Fe₂O₄-MWCNTs composites were prepared by sol-gel route. The samples were sintered at 750-950 °C and were characterized by XRD, FESEM, HRTEM and Raman spectroscopy. Single phase of Ni_0.8Zn_0.2Fe₂O₄ having [3 1 1] major peak was obtained by sol-gel method at 750 °C and 950 °C. FESEM micrographs show that grain size increases with the increase of sintering temperature and ranges from 24 to 60 nm. FESEM and HRTEM results showed coating of Ni_0.8Zn_0.2Fe₂O₄ on MWCNTs and show better morphology at the sintering temperature of 750 °C. The magnetic properties measured from impedance vector network analyzer showed that sample (Ni_0.8Zn_0.2Fe₂O₄-MWCNTs) sintered at 750 °C have higher initial permeability (20.043), Q-factor (50.047), and low loss factor (0.0001) as compared Ni_0.8Zn_0.2Fe₂O₄-MWCNTs sintered at 950 °C. Due to better magnetic properties, Sample (Ni_0.8Zn_0.2Fe₂O₄-MWCNTs sintered at 750 °C) composites were used as magnetic feeders for the EM transmitter. It was found that magnitude of EM waves from EM transmitter increased up to 243% by using Ni_0.8Zn_0.2Fe₂O₄-MWCNTs polymer composites.     

ZrxCo0.8−xNi0.2−xFe2O4-graphene nanocomposite for enhanced structural,dielectric and visible light photocatalytic applications

Zirconium doped nickel cobalt ferrite (Zr_xCo_0.8−xNi_0.2−xFe₂O₄) nanoparticles and Zr_xCo_0.8−xNi_0.2−xFe₂O₄-graphene nanocomposites were synthesized by a cheap and facile co-precipitation method. Annealing was done at 750 °C for 6.5 h. Spinel cubic structure of prepared nanoparticles was confirmed by X-ray powder diffraction (XRD) technique. Crystalline size of nanoparticles was observed in the range of 18–27 nm. Graphene was synthesized by Hummer's method. Formation of rGO was confirmed by UV-visible spectroscopy (UV-vis) and XRD. Zr_xCo_0.8−xNi_0.2−xFe₂O₄-graphene nanocomposites were prepared by ultra-sonication route. Grain size of nanoparticles and dispersion of nanoparticles between rGO layers was determined by Scanning electron microscopy (SEM). In application studies of nanoparticles and their nanocomposites, photocatalytic efficiency of nanoparticles under visible light irradiation was observed by degradation of methylene blue. Charge transfer resistance was measured by electrochemical impedance spectroscopy (EIS) and the variation in dc electrical resistivity was analyzed by room temperature current voltage characteristics (I-V). Dielectric constant was also evaluated in frequency range from 1 MHz to 3 GHz. All these investigations confirmed the possible utilization of these materials for a variety of applications such as visible light photocatalysis, high frequency devices fabrication etc.     

Cation distribution and magnetic analysis of wideband microwave absorptive CoxNi1−xFe2O4 ferrites

Co_xNi_1−xFe₂O₄ ferrites (x=0, 0.2, 0.4, 0.4, 0.6, 0.8 and 1) were prepared by a sol-gel auto-combustion method. The samples were structurally characterized by X-ray diffractometry (XRD), field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray analysis (EDX), and Fourier transform infrared spectroscopy (FTIR). The XRD patterns confirmed single phase formation of spinel structure. Cation distribution estimated from XRD data suggested the mixed spinel structure of ferrite. The EDX analysis was in good agreement with the nominal composition. The results of FTIR analysis indicated that the functional groups of Co-Ni spinel ferrite were formed during the combustion process. According to FE-SEM micrographs, by addition of cobalt ion the average particle size of substituted nickel ferrite was gradually became smaller from 450 nm to 280 nm. Magnetic measurement using vibrating sample magnetometer (VSM) showed an increase in saturation magnetization and coercivity by Co²⁺ substitution in nickel ferrite. For Co_0.8Ni_0.2Fe₂O₄ sample, M_s and H_c reaches as high as 93 emu/g and 420 Oe, respectively. The reflection loss properties of the nanocomposites were investigated in the frequency range of 8–12 GHz, using vector network analyzer (VNA). Cobalt substitution could enhance reflection loss of NiFe₂O₄ ferrite. The maximum reflection loss value of the Co²⁺ substituted Ni ferrite was ~ −26 dB (i.e. over 99% absorption) at 9.7 GHz with bandwidth of 4 GHz (RL<– 10 dB) through the entire frequency range of X-band.     

Structural,dielectric and magnetic manifestation in BaM/PEEK nanocomposite for X band shielding blocks

The microwave absorber nanocomposites consisting of substituted M-type hexaferrite Ba_0.8Gd_0.2Fe_11.5Co_0.5O₁₉ and polyetheretherketone (PEEK) have been investigated for X-band applications. Composites with hexaferrite to PEEK ratios 5:0, 4:1, 3:2, 2:3, 1:4, 0:5 have been synthesized by a micro-emulsion method. XRD results confirm the hexagonal structure of the hexaferrite with average crystallite size up to 37.2 nm. Magnetic properties reveal that saturation magnetization M_s increases whereas coercivity H_c decreases by increasing the ferrite content in the composites. Complex permittivity and permeability have been tailored with ferrite content in the X-band. The dielectric constant reduces from 5.3 to 3.25 while permeability increases up to 1.37 with increasing ferrite concentrations. The microwave results show the minimum reflection loss of ?10.79 dB for composite with 80% ferrite.     

Porous Fe3O4/C microspheres for efficient broadband electromagnetic wave absorption

Porous Fe₃O₄/C microspheres, which were Fe₃O₄ nanocrystals (～8?nm) embedded in an open nanostructured carbon network, were successfully synthesized via a facile hydrothermal process. The porous Fe₃O₄/C microspheres possessed many distinct attributes that facilitate efficient broadband electromagnetic wave absorption (EMWA). EMWs were attenuated through multiple reflections and absorption in the 3D interconnected porous structure of the microspheres; these processes collectively improved the interaction between the EMWs and the absorber. Additionally, the carbon network and embedded Fe₃O₄ nanoparticles caused significant dielectric losses and magnetic losses, respectively, which also enhanced EMWA. The EMWA characteristics of the microspheres could be precisely tuned via changing the carbon content to achieve optimized impedance matching. Porous Fe₃O₄/C microspheres with a 71.5?wt% carbon content displayed particularly impressive EMWA properties: a maximum reflection loss (RL) value of ??31.75 across broad band frequencies in the range of 7.76–12.88?GHz (RL < ?10?dB) at an absorber thickness of 3.0?mm. These excellent EMWA properties may be attributed to both dielectric loss (carbon) and magnetic loss (Fe₃O₄). Additionally, the 3D interconnected porous structure of the Fe₃O₄/C microspheres is especially favorable for impedance matching.     

Single and double-layered Tri-band Microwave absorbing materials

Absorbers at microwave frequencies with multiple frequency-band response are particularly important for use in military for stealth technology. Specially, ferrite based absorbing materials are significant for electromagnetic shielding and signal attenuation. The enhancement of reflection loss of ferrites along with carbonaceous materials are even more beneficial. Recently double-layer absorbers have extensively studied to meet the requirements of advanced absorbing materials in multiple frequency-band response. It still remains a challenge how to determine the type and thickness to couple the impedance-matching-layer to the absorption-layers for a double-layer absorber. We applied hydrothermal method to prepare Fe₃O₄ nanoparticle and combine them with either graphene oxide (GO) or reduced graphene oxide (rGO) to prepare a composite of specific quality to obtain Fe₃O₄@GO and Fe₃O₄@rGO nanocomposite. We studied microwave attenuation capabilities of single and double-layer absorbers containing these two materials. We have demonstrated that with a thin impedance matching layer as a first layer and an absorbing layer behind this layer for the double-layered absorber has much higher reflection loss (RL) than a single-layer. The Fe₃O₄@rGO composite as a single-layer absorber shows the best microwave absorption performance with RL close to −30 dB in all three microwave bands (X, Ku and K bands). The use of a double-layer structure as Fe₃O₄@GO as impedance matching layer and Fe₃O₄@rGO as absorbing layer exhibits the best absorption of −50 dB. This is much larger than the single-layered absorbers at all three frequency-bands. Such a performance is superior to many reported ferrite-based carbonaceous composites. Therefore, a double-layer absorber is best suited to coat the whole body of the aircraft or missiles to evade satellite detection, a preparation towards new-generation weapons for future warfare. Before performing the absorption studies we have characterized the ferrites, GO and rGO materials with various microstructural and magnetic characterizations.     

Rhombic Fe2O3 lumps doping hollow ZnFe2O4 spheres through oxidative decomposition process implanted into graphene conductive network with superior electromagnetic wave absorption properties

Conductor-dielectric-magnetic multicomponent coordination composites with rhombic Fe₂O₃ lumps doping hollow ZnFe₂O₄ spheres through oxidative decomposition process implanted into graphene conductive network (hollow ZnFe₂O₄ spheres/rhombic Fe₂O₃ lumps/rGO composites) were successfully constructed by a facile method. The countless hollow ZnFe₂O₄ spheres were compactly attached to the curled-paper rGO and larger sized-rhombic Fe₂O₃ lumps were relatively dispersed. Among, the hollow structure of ZnFe₂O₄ spheres could attenuate the electromagnetic wave by multiple reflections and scatterings. Intriguingly, hollow ZnFe₂O₄ spheres reacted with GO to form intermediate rhombic Fe₂O₃ lump products, which ameliorated the hetero-interfaces structure and helped to improve impedance matching by weakening the strong magnetic ZnFe₂O₄ (M_s = 91.2 emu/g) and high conductive rGO after the introduction of weakly magnetic Fe₂O₃ semiconductor. Moreover, all three components could induce dielectric polarization losses, such as multilayer or dipole polarization. Therefore, the maximum absorption of ternary composites was up to ?64.3 dB at 7 GHz and 3.4 mm, simultaneously, and a bandwidth exceeding ?10 dB was 4.2 GHz at 1.7 mm. Meanwhile, with a thin thickness range of 1.5–5 mm, the absorption bandwidth below ?10 dB was from 2 to 18 GHz which occupied for 91.5% of whole study frequency range. These results provided a new approach and reference for the design and property regulation of electromagnetic materials at electronic communications, aerospace and military radar flied.     

Template-free synthesis of rGO decorated hollow Co3O4 nano/microspheres for ethanol gas sensor

A series of the rGO decorated hollow Co₃O₄ spheres were fabricated via a solvothermal-combination-calcination process with no template. The morphological and crystal structure analysis were carried out through several characterization techniques, including SEM, TEM, XRD and XPS. The results indicate that the hollow Co₃O₄ microspheres were assembled by nanoparticles with an average diameter of 20?nm and adhered uniformly on rGO nanosheets. According to the gas sensing test, 3?wt% rGO-Co₃O₄ hollow spheres showed a higher substantial response to 100?ppm ethanol reaching up to 13.5, which is 3.7 times than the pristine Co₃O₄ at 180?°C. In addition, it also exhibited short response-recovery time and good reproducibility. The enhanced sensing properties probably come from the synergy between rGO and Co₃O₄, mesoporous structure, and its high specific surface area (108.2?m²/g). This facile method could be used for the fabrication of many advanced materials for sensors, capacitors and electrodes.     

The effect of GO loading on electromagnetic wave absorption properties of Fe3O4/reduced graphene oxide hybrids

Ideal electromagnetic absorbing materials with lightweight and high efficiency have broad application outlook in military and civil fields. In this work, a 3D nanostructure material by hybridizing Fe₃O₄ nanocrystals and reduced graphene oxide (Fe₃O₄/rGO) were synthesized through an environmental-friendly one-pot solvothermal method. The effect of GO loading on electromagnetic (EM) wave absorption characteristic of Fe₃O₄/rGO was investigated. The introduction of rGO sheets not only prevented Fe₃O₄ from agglomerating, also improved the absorption performance of Fe₃O₄/rGO hybrids. With an appropriate addition, Fe₃O₄/rGO obtained a minimum reflection loss (RL) of −22.7 dB and the absorption bandwidth was 3.13 GHz (90% absorption).     

Synthesis and characterization of calcium double perovskites for the potential application of semiconducting CO2 sensors

A conventional solid-state sintering method was used to prepare double perovskite structured compounds BCN (Ba₂Ca_0.67Nb_1.33O₆), BCNCo (Ba₂Ca_0.67Nb_1.33-xCo_xO_6-δ) and BCNCoFe (Ba₂Ca_0.67Nb_0.67Co_0.66-yFe_yO_6-δ), which exhibit significant chemical stability in nitrogen, air, and 2 % CO₂ (balanced by nitrogen). SEM images show that the Co dopant causes a dense microstructure for BCNCo compounds. In contrast, the introduction of Fe tends to produce a porous and web-like microstructure for the BCNCoFe series. Ba₂Ca_0.67Nb_0.67Co_0.66O_6-δ has a reasonable response (recovery) time at 750 °C and it seems suitable for CO₂ detection at elevated temperatures. Among the BCNCoFe compounds, Ba₂Ca_0.67Nb_0.67Co_0.33Fe_0.33O_6-δ has the largest capacitance as the CO₂ concentration changes from 0 to 2000 ppm, and it exhibits satisfactory sensitivity and repeatability in the temperature range of 450–700 °C with an extra voltage of 0.1 V. To further consider the Ba₂Ca_0.67Nb_0.67Co_0.33Fe_0.33O_6-δ compound for CO₂ sensing, a sol-gel method was utilized. The sol-gel-prepared Ba₂Ca_0.67Nb_0.67Co_0.33Fe_0.33O_6-δ senses CO₂ well, and its concentration changes from 0 to 2000 ppm (or from 0 to 300 ppm) in the temperature range of 400–600 °C. The different CO₂ sensing properties of all prepared double perovskite compounds can be interpreted by the different surface areas that play critical roles in the chemical adsorption of related gaseous species.     

Fe3O4-intercalated reduced graphene oxide nanocomposites with enhanced microwave absorption properties

Fe₃O₄-intercalated reduced graphene oxide (Fe₃O₄-rGO) nanocomposites were synthesized by an in situ reduction process. The results of XRD and XPS analyses suggested the successful formation of a Fe₃O₄ crystal phase within the rGO sheets. The SEM and TEM images demonstrated that Fe₃O₄ was flaky and was inserted stably within the rGO layers to form a typical sandwich-like structure. The hysteresis loops revealed the superparamagnetic behavior of the Fe₃O₄-rGO nanocomposites at room temperature. The electromagnetic parameters revealed that Fe₃O₄-rGO nanocomposites exhibited multiple dielectric relaxation and magnetic resonance. The reflection loss revealed that the maximum loss was −49.53 dB at 6.32 GHz for a thickness of 3.4 mm while the highest effective absorption bandwidth was 2.96 GHz.     

Fabrication and characterization of polymer composites surface coated Fe3O4/MWCNTs hybrid buckypaper as a novel microwave‐absorbing structure

A naval hybrid buckypaper was fabricated by vacuum filtration method with monodispersion solution of Fe₃O₄ decorated Multiwalled carbon nanotubes (MWCNTs). The morphology, element composition and phase structure of hybrid buckypaper were characterized by field‐emission scanning electron microscope, energy dispersive spectrometer, and X‐ray diffraction. The microwave absorption and complex electromagnetic properties of the composites surface coated MWCNTs buckypaper (or Fe₃O₄/MWCNTs hybrid buckypaper) have been investigated in the frequency range of 8–18 GHz. The results indicate that the microwave absorption properties of composite structure have been evidently improved due to the Fe₃O₄/MWCNTs hybrid buckypaper' high magnetic loss and suitable dielectric loss properties. The reflection loss of composite surface coated Fe₃O₄/MWCNTs hybrid buckypaper (with a matching thickness d = 0.1 mm) is below ?10 dB in the frequency range of 13–18 GHz, and the minimum value is ?15.3 dB at 15.7 GHz. Thus, Fe₃O₄/MWCNTs hybrid buckypaper can become a promising candidate for electromagnetic‐wave‐absorption materials with strong‐absorption, thin‐thickness and light‐weight characteristics. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41974.     

Fabrication of Nd-doped Ni–Zn ferrite/multi-walled carbon nanotubes composites with effective microwave absorption properties

The electromagnetic materials are featured by good magnetic permeability and dielectric constant characteristics, which are of significant importance in solving the pollution problem of electromagnetic. In this study, after the complete of the use of sol-gel method, argon gas was then introduced for calcination, and eventually a new type of MWCNTs/Ni_0.5Zn_0.5Nd_0.04Fe_1.96O₄ composites was synthesized after the above mentioned procedures. The synthesized MWCNTs were able to be adsorbed on the surface of Ni_0.5Zn_0.5Nd_0.04Fe_1.96O₄ and could form a good conductive work of 3D. Also, the effect of additional MWCNTs on microwave absorption properties of MWCNTs/Ni_0.5Zn_0.5Nd_0.04Fe_1.96O₄ composites were also observed in this study. The results indicate that the additional MWCNTs function to significantly improve the microwave absorption property of MWCNTs/Ni_0.5Zn_0.5Nd_0.04Fe_1.96O₄. Through altering the amount of MWCNTs, the microwave attenuation performance and impedance matching coefficient of this electromagnetic materials can be effectively improved. The S2 sample presented a minimum reflection loss of ?35.05 dB when its thickness reached 1.6 mm, meanwhile, the effective absorption bandwidth achieved 4.55 GHz. The prepared composites perform well in microwave absorption, which can attribute to the reasonable ratio of composites as well as its interaction with both of the magnetic and dielectric components. This research paved the way for novel ideas to be put in the electromagnetic absorption materials with high-efficient.     

Hollow polyaniline/Fe3O4 microsphere composites: Preparation,characterization, and applications in microwave absorption

Hollow polyaniline/Fe₃O₄ microsphere composites with electromagnetic properties were successfully prepared by decorating the surface of hollow polyaniline/sulfonated polystyrene microspheres with various amounts of Fe₃O₄ magnetic nanoparticles using sulfonated polystyrene (SPS) as hard templates and then removing the templates with tetrahydrofuran (THF). The synthesized hollow microsphere composites were characterized by FT-IR, UV/Vis spectrophotometry, SEM, XRD, elemental analysis, TGA, and measurement of their magnetic parameters. Experimental results indicated that the microspheres were well-defined in size (1.50–1.80 μm) and shape, and that they were superparamagnetic with maximum saturation magnetization values of 3.88 emu/g with a 12.37 wt% content of Fe₃O₄ magnetic nanoparticles. Measurements of the electromagnetic parameters of the samples showed that the maximum bandwidth was 8.0 GHz over ?10 dB of reflection loss in the 2–18 GHz range when the Fe₃O₄ content in the hollow polyaniline/Fe₃O₄ microsphere composites was 7.33 wt%.