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.     

Assembled porous Fe3O4@g-C3N4 hybrid nanocomposites with multiple interface polarization for stable microwave absorption

Magnetic/dielectric composites can offer good electromagnetic impendence. However, the strategy for embodying strong absorbing ability and broad effective absorption band simultaneously is a significant challenge. Therefore, assembled porous Fe₃O₄@g-C₃N₄ hybrid nanocomposites have been designed and synthesized, in which porous Fe₃O₄ nanospheres assembled by ~ 3?nm Fe₃O₄ nanoparticles are surrounded by g-C₃N₄. The introduction of g-C₃N₄ improves dielectric loss ability at 2–18?GHz and magnetic loss ability at 2–10?GHz, and enhances attenuation constant, and increases electromagnetic impedance degree. These merits ensure that assembled porous Fe₃O₄/g-C₃N₄ hybrid nanocomposites deliver superior microwave absorption performance, such as effective absorption bandwidth, f_E, (reflection loss less ??10?dB) exceeding 5?GHz at 2.0–2.3?mm, the maximal f_E of 5.76?GHz and minimal reflection loss of at least ??20?dB with thickness ranging from 2.3 to 10.0?mm, avoiding the sensitivity of absorption properties to absorbing layer thickness. Stable microwave absorbing performance originates from multi-interfacial polarization, multi-reflection, enhanced electromagnetic loss capability, and good electromagnetic impedance. Our study offers a new idea for stable microwave absorber at 2–18?GHz.     

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.     

Facile synthesis of a novel flower-like BiFeO3 microspheres/graphene with superior electromagnetic wave absorption performances

In recent years, porous or layered magnetic materials have received increasing attention due to their low density and lightweight. In this work, porous BiFeO₃ microspheres and three-dimensional porous BiFeO₃ microsphere-reduced graphene oxide (RGO) composite (3D porous BiFeO₃/RGO) were prepared by one-step etching processing using pure BiFeO₃ particles as precursors. The precursor undergoes dissolution-recrystallization/reduction process, resulting in large amount of BiFeO₃ fragments and graphene hybrid product, which forms 3D porous BiFeO₃/RGO composite. Electromagnetic (EM) absorption performance measurements exhibit that at low thickness of 1.8?mm, porous BiFeO₃/RGO composite can achieve reflection loss (R_L) value up to ?46.7?dB and absorption bandwidth (defined by R_L <?10?dB) exceeding 4.7?GHz (from 12.0 to 16.7?GHz), testifying outstanding microwave absorbing performance. Compared with pure porous BiFeO₃, improved EM wave absorption ability of as-prepared porous BiFeO₃/RGO composite is attributed to interfacial polarization, multiple reflections, scattering, and appropriate impedance matching.     

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.     

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.     

Design of magnetic triple-shell hollow structural Fe3O4/FeCo/C composite microspheres with broad bandwidth and excellent electromagnetic wave absorption performance

A three-step strategy combining solvothermal and liquid phase reduction method had been developed for preparation of magnetic triple-shell hollow structural Fe₃O₄/FeCo/C (TSH–Fe₃O₄/FeCo/C) composite microspheres. FeCo was used to enhance electromagnetic (EM) wave absorption in different frequency band and broaden effective absorbing bandwidth, while carbon was used to improve impedance matching. Triple-shell hollow structure was designed to enrich the multiple interfaces to favor the interfacial polarization, increase the multiple reflections and scattering, and provide physicochemical protection to Fe₃O₄ core from oxidation. The microstructure and morphology of TSH-Fe₃O₄/FeCo/C composite microspheres were characterized by TEM, XRD and Raman in detail. The results indicated that magnetic Fe₃O₄ was completely covered by FeCo and carbon via layer by layer. As an EM wave absorber, the maximum reflection loss of TSH-Fe₃O₄/FeCo/C composite microspheres was up to -37.4 dB due to better normalized characteristic impedance at a thickness of 2.2 mm and the bandwidth less than -10 dB even reached up to 5.9 GHz. The excellent EM wave absorption performance was attributed to the combination of shell materials (Fe₃O₄, FeCo and carbon) and unique triple-shell hollow structure, which lead to multiple relaxation processes and good impedance matching. Consequently, this work would contribute to the design and preparation of high performance EM wave absorbent with outstanding absorbing property and wider absorption range.     

Magnetite/graphene oxide/Prussian blue composite with robust effectiveness for electromagnetic interference shielding

Considering the promising efficiency of composites, in the current study, a graphene oxide (GO)-magnetite-Prussian blue (PB) composite material was prepared. The composite exhibited electrical conductivity, magnetic permeability, and permittivity nature, and was evaluated using electromagnetic interference (EMI) shielding studies. GO was developed by the Hummer's method, ferrite (Fe₃O₄) was incorporated by the sol-gel method, and PB was introduced in the mixture by an in-situ process. The fabricated samples were studied by X-ray diffraction, Raman Spectroscopy, Fourier-transform infrared spectroscopy along with EMI shielding efficiency (SE) evaluation. The SE of ?71.66 dB of reflection losses was measured at a frequency of 1.5 MHz. The GO/Fe₃O₄/PB composite provided the best results for the detection in the 1–18 MHz frequency range because of its excellent electric and magnetic properties. The obtained results demonstrated that the GO/Fe₃O₄/PB composite has promising potential applications in EMI shielding.     

Preparation of pod-like 3D Ni0.33Co0.67Fe2O4@rGO composites and their microwave absorbing properties

The ferrite/reduced graphene oxide (rGO) composites have attracted increasing attention due to the combination of the dielectric loss of rGO and the magnetic loss of ferrites. In this paper, pod-like 3D Ni_0.33Co_0.67Fe₂O₄@rGO composites were prepared using a solvothermal reaction followed by cold quenching. The structures and morphologies of as obtained composites were characterized using X-ray diffractometer, Raman microscope, photoelectron spectroscopy, scanning electron microscope and transmission electron microscope. The Ni_0.33Co_0.67Fe₂O₄ microspheres with a diameter of 100–150?nm were wrapped in rGO rolls due to the shrinkage of rGO in liquid nitrogen. The rGO sheets with ferrite microspheres wrapped in form the pod-like 3D network morphology. The minimum reflection loss of as-prepared composites reaches ?47.5?dB and the absorption bandwidth (RL<?10?dB) is 5.02?GHz. The composites show much better absorbing performances than pure Ni_0.33Co_0.67Fe₂O₄ microspheres and Ni_0.33Co_0.67Fe₂O₄-rGO mixture formed by mechanically blending of cold quenched pure rGO and ferrite microspheres.     

Preparation of Fe3O4 particles from copper/iron ore cinder and their microwave absorption properties

In this study, magnetic Fe₃O₄ particles were prepared from copper/iron ore cider by precipitation oxidization method. The yield of Fe was 82.6 at%. XRD, TEM, SEM, EDS and microwave network analyzer were used to characterize the particles. The results showed that Fe₃O₄ particles were well crystallized and possessed an octahedral morphology, and the crystal size was about 200 nm; the sample with 70 wt% Fe₃O₄ exhibited the optimal absorbing ability, the minimum reflection loss was ?42.7 dB at 14.08 GHz and the bandwidth less than ?10 dB was about 4.2 GHz when the sample thickness was 1.9 mm. It was clearly demonstrated that the Fe₃O₄ particles prepared from copper/iron ore cider could be used as an effective microwave absorbing material.     

Electrochemically exfoliated graphene oxide/iron oxide composite foams for lithium storage,produced by simultaneous graphene reduction and Fe(OH)3 condensation

We describe the production of graphene-based composites for energy storage, obtained by a combination of electrochemical and solution processing techniques. Electrochemically exfoliated graphene oxide sheets (EGO) are produced using an original setup that allows fast expansion of graphite flakes and efficient exfoliation of expanded graphite via an electrochemical route. The sheets are deposited on a sacrificial nickel foam together with an iron hydroxide colloidal precursor. Calcination treatment simultaneously renders the EGO foam conductive and transforms Fe(OH)₃ into hematite (α-Fe₂O₃), yielding a nanoporous Fe₂O₃ layer on the surface of the mesoporous EGO foam, creating an ideal structure for lithium storage. The obtained graphene/metal oxide hybrid is a continuous, electrically conductive three-dimensional (3D) composite featuring a hierarchical meso–nano porous structure. A systematic study of these composites, varying the Fe₂O₃:EGO ratio, is then performed to maximize their performance as nanostructured electrodes in standard coin cell batteries.     

One-step hydrothermal synthesis and microwave electromagnetic properties of RGO/NiFe2O4 composite

The reduced graphene oxide (RGO)/NiFe₂O₄ composite was synthesized by a facile one-pot hydrothermal route, which avoided the usage of chemical reducing agent. The reduction of graphene oxide (GO) and the crystallization of NiFe₂O₄ crystals happened in a one-step hydrothermal process. The morphology, microstructure and magnetic properties of the composite were detected by means of XRD, XPS, TEM, EDX, TG-DSC and VSM. The maximum R_L of the RGO/NiFe₂O₄ composite is −39.7 dB at 9.2 GHz with the thickness of 3.0 mm, and the absorption bandwidth with the R_L below −10 dB is up to 5.0 GHz (from 12.7 to 17.7 GHz) with a thickness of 1.9 mm. The introduction of RGO signally enhanced microwave absorption performance of the NiFe₂O₄ NPs. It is believed that such composite will be applied widely in microwave absorbing area.     

Synthesis of nitrogen-doped graphene-based binary composite aerogels for ultralightweight and broadband electromagnetic absorption

The development of ultralightweight and broadband electromagnetic wave (EMW) absorbing materials remains a big challenge. In this work, porous magnesium ferrite microspheres decorated nitrogen-doped reduced graphene oxide (NRGO/MgFe₂O₄) composite aerogels were prepared by a two-step route of solvothermal synthesis and hydrothermal self-assembly. Results of microscopic morphology characterization showed that NRGO/MgFe₂O₄ composite aerogels had a unique hierarchical porous structure. Moreover, the influence of additive amounts of graphene oxide on the electromagnetic parameters and EMW absorption properties of NRGO/MgFe₂O₄ composite aerogels was explored. Remarkably, the attained binary composite aerogel with the content of NRGO of 70.21 wt% exhibited the best EMW absorption performance. The minimum reflection loss reached up to −55.7 dB, and the corresponding effective absorption bandwidth was as large as 5.36 GHz at a thin matching thickness of 1.98 mm. Furthermore, when the matching thickness was slightly increased to 2.29 mm, the widest effective absorption bandwidth was enlarged to 7.1 GHz, covering the entire Ku-band. The magnetodielectric synergy and unique hierarchical porous structure in NRGO/MgFe₂O₄ composite aerogels not only improved the impedance matching, but also greatly enhanced the EMW absorption capacity. It was believed that the results of this work could be helpful for the preparation of graphene-based magnetic composites as broadband and efficient EMW absorbers.     

High dielectric and microwave absorption properties of ultra-thin 1-xSrTiO3-δ − xSrAl12O19 films

To reduce the thickness of the microwave absorbing materials, we have prepared 1-xSrTiO_3-δ?xSrAl₁₂O₁₉ ceramics by hot?pressing sintering in the vacuum. The microstructure, dielectric, thermogravimetric analysis and microwave absorbing properties of 1-xSrTiO_3-δ?xSrAl₁₂O₁₉ were systematically investigated and discussed. The 0.95SrTiO_3-δ??0.05SrAl₁₂O₁₉ has high permittivity, the real part is from 1662.2 to 704.9 and the imaginary part is from 208.6 to 12. The absorption bandwidth (reflection loss ≤?5?dB) of 0.95SrTiO_3-δ??0.05SrAl₁₂O₁₉ can cover 8.6???12.4?GHz and its thickness is only 0.232?mm which is much thinner than these recently reported by other researchers. For 0.942SrTiO_3-δ??0.058SrAl₁₂O₁₉, the peak value of reflection loss is up to ??58.5?dB with a thickness of 0.75?mm. The 1-xSrTiO_3-δ?xSrAl₁₂O₁₉ films could be excellent candidates for highly efficient and ultra?thin microwave absorbing materials.     

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.     

Modulation of electromagnetic wave absorption by carbon shell thickness in carbon encapsulated magnetite nanospindles–poly(vinylidene fluoride) composites

A series of Fe₃O₄/C core–shell nanospindles with different shell thickness have been synthesized by a wet chemical method and subsequent high-temperature carbonization. The thickness of carbon shell can be well adjusted from 9 to 32 nm by changing the addition amounts of resorcinol and formaldehyde precursors during the coating process. Structure and morphology characterizations reveal that the carbon shell is amorphous structure and uniformly encapsulates on porous Fe₃O₄ nanospindles. For the first time, a flexible Fe₃O₄/C/poly(vinylidene fluoride) (PVDF) composite absorber was prepared by embedding the core–shell Fe₃O₄/C nanospindles in PVDF matrix. The electromagnetic properties of the composite show strong dependence on the carbon-shell thickness. The impedance matching for electromagnetic absorption is improved by the synergy effect between Fe₃O₄ nanospindles and encapsulated carbon shell. The Fe₃O₄/C/PVDF composite with thick carbon shell exhibits strong electromagnetic wave absorbing ability with thin absorber thickness. The minimum reflection loss for the absorber with thickness of 2.1 mm can reach −38.8 dB.     

Preparation of Three-Dimensional Co3O4/graphene Composite for High-Performance Supercapacitors

Here, we developed a simple and efficient route for the preparation of three-dimensional (3D) Co₃O₄-anchored graphene composites using the sacrificial template-assisted method and the subsequent deposition process of Co₃O₄ nanoparticles. As structural guiding materials, polystyrene (PS) spheres provide 3D porous architectures with a high surface area. 3D porous graphene materials serve as conductive supporters for the deposition of Co₃O₄ nanoparticles through precipitation growth. The 3D porous composite structures of Co₃O₄/graphene composites were intensively investigated using scanning electron microscope, transmission electron microscope, and X-ray diffraction. The 3D Co₃O₄/graphene composites show a high specific capacitance of 328?F?g^?1 with efficient and fast charge–discharge process in aqueous 6?M KOH electrolyte. In addition, the composites provide a good cycle lifetime, which retained 98% capacitance retention over 2000 cycles.     

Electromagnetic properties of electrospun Fe3O4/carbon composite nanofibers

In order to develop multifunctional nanofibers, the electrical conductivity and magnetic properties of Fe₃O₄/carbon composite nanofibers have been examined. Polyacrylonitrile (PAN) is used as a matrix to produce magnetic composite nanofibers containing different amounts of magnetite (Fe₃O₄) nanoparticles. Electrospun composite nanofibers were thermally treated to produce electrically conductive and magnetically permeable composite carbon nanofibers. The composite nanofibers were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffractometry (XRD), Raman spectroscopy, four-point probe and Superconducting Quantum Interference Device (SQUID). Uniform nanofibers were obtained with successful transferring of magnetic properties of Fe₃O₄ into the as-spun composite nanofibers. The electromagnetic properties were tuned by adjusting the amount of Fe₃O₄ in the matrix and carbonization process. The electrical conductivity, magnetic moment and also magnetic hysteresis rise up by adding Fe₃O₄ and increasing carbonization temperature. The high surface area provided by the ultrafine fibrous structures, the flexibility and tuneable electromagnetic properties are expected to enable the expansion of the design options for a wide rage of electronic devices.     

Effect of Fe3O4 concentration on 3D gel-printed Fe3O4/CaSiO3 composite scaffolds for bone engineering

In this study, porous calcium silicate (CaSiO₃) scaffolds were prepared by 3D gel-printing (3DGP) method and Fe₃O₄ water-based magnetic fluids (WMFs) were prepared by phacoemulsification compound chemical coprecipitation method. Fe₃O₄ WMFs were coated on CaSiO₃ scaffolds surface to prepare Fe₃O₄/CaSiO₃ composite scaffolds. The effect of WMFs with different Fe₃O₄ concentrations on porous CaSiO₃ scaffolds was studied. The composition and morphological characteristics of porous scaffolds were analyzed by using scanning electron microscope (SEM) and energy dispersive spectrometer (EDS) analysis. The magnetic properties were tested by vibrating sample magnetometer (VSM). The stability of Fe₃O₄ WMFs coatings and the degradability of composite scaffolds were tested by immersing them in simulated body fluid (SBF). The results show that when Fe₃O₄ concentration was 5.4% (w/v), the composite scaffolds had the highest saturation magnetization of 69.6 emu/g and the best stability in dynamic SBF. It is obviously that Fe₃O₄ WMFs coatings can be used for bone tissue engineering scaffolds repairing.     

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).