Hollow Fe3O4 Research Articles

Ultra-lightweight asymmetric hierarchical porous structure for high-efficiency absorption-dominated electromagnetic interference shielding

In this work, ultra-lightweight composite aerogels with a hierarchical pore structure consisting of hollow Fe3O4 microspheres (∼250 nm), hollow MXene microspheres (∼580 nm) and pores (10∼40 μm) in polyimide (PI) aerogel are developed through directional freezing, followed by freeze drying and thermal annealing. The composite aerogels exhibit a distinct asymmetric structure, with a top Fe3O4/PI aerogel layer designed for impedance matching and a bottom MXene/PI aerogel layer aimed at enhancing attenuation. This deliberate structure design not only reduces the density of the composite aerogels but also greatly enhances their absorption of electromagnetic waves. The composite aerogel demonstrates an impressive X-band EMI SE of 69.7 dB, a remarkable absorption coefficient (A) of 0.73, and an excellent surface-specific SE (SE divided by material density and thickness) of 13352 dB cm2 g-1, achieved at a density of just 0.034 g/cm³. Moreover, the composite aerogel exhibits outstanding stability in compression and shielding performance. Following 100 cycles of compression, the compressive strength remains at 94.9% of the initial compressive strength (98 kPa), and its EMI SE maintains 68.5 dB with a retention rate of 98.2%. Additionally, the composite aerogel presents outstanding thermal insulation (0.046 W m-1 K-1) and thermal resistance (initial decomposition temperature > 500 °C). This work provides novel insights into the design and fabrication of ultra-lightweight and absorption-dominated EMI shielding materials.

Fabrication of hollow Fe3O4 microspheres encapsulated by single-walled carbon nanohorns for high-performance microwave absorption

Due to the increasingly serious electromagnetic radiation and pollution problems, it is urgent to develop high-performance electromagnetic wave absorbing materials. Herein, the hollow Fe3O4 microspheres encapsulated by single-walled carbon nanohorns (H-Fe3O4@SWCNHs) have been synthesized via facile solvothermal approach. The obtained H-Fe3O4@SWCNHs composite exhibits a unique hollow core-shell structure and superior microwave absorption performance. When the matching thickness is 2.0 mm, the composite shows a minimum reflection loss value of −42.2 dB at 13.6 GHz and a maximum effective absorption broadband value of 6.2 GHz covering from 11.8 to 18 GHz. The excellent microwave absorption performance of the H-Fe3O4@SWCNHs composite is mainly attributed to the unique hollow core-shell structure, optimal impedance matching, and synergistic effects of dielectric loss and magnetic loss. Therefore, the present work provides a new kind of ideal microwave absorbing material with light weight, thin thickness, wide bandwidth and strong absorption capability for high-performance microwave absorption.

Sea urchin-like Fe3O4 hollow microspheres/fatty amines composites phase change materials for highly efficient light-to-thermal conversion and heat storage

Pure phase change materials (PCMs) have limited photothermal conversion capabilities. To improve the photothermal conversion capability of PCMs, we developed composite phase change materials (FHS@PCMs) of sea urchin-like Fe3O4 hollow spheres (FHS) loaded with fatty amines (hexadecylamine (HDA) and octadecylamine (ODA)). The material composition and the surface nano-raised structure of FHS enable FHS@PCMs to exhibit excellent light absorption (up to 90 %, without any additional modification) and thermal conductivity. Moreover, the internal hollow spherical structure would prevent the leakage of PCM during the phase change process. Interestingly, FHS and FHS@PCMs exhibit inherent superhydrophobic properties with a water contact angle greater than 150°, thus endowing them with self-cleaning properties. FHS possesses strong magnetic properties that aid in material collection. Furthermore, the prepared FHS@PCMs exhibited exceptional thermal properties. The latent heat of FHS@HDA and FHS@ODA was 139.21 J∙g−1 and 140.13 J∙g−1, respectively. Additionally, FHS@PCMs maintained their excellent thermal properties even after 50 and 100 thermal cycles. Under one solar radiation, FHS@PCMs show a photothermal conversion efficiency of 89.63 % and 88.02 %, respectively. Taking of these advantages, the as-prepared composite phase change material may have significant potential in the fields of solar energy conversion and storage.

A multifunctional platform based on ZIF-67 templated NiCo-LDH and Fe3O4 hollow spheres for photocatalytic CO2 conversion and supercapacitors

This work presented a series of hybrid materials F@P-LDHs exhibiting the core-shell structure with PPy as the interface modifier, explored as dual-functional materials for studying photocatalytic reduction of CO2 and electrochemical behaviors. F@P-LDHs served as photocatalysts, effectively convert CO2 into CO without using any sacrificial agents and photosensitizers via the gas-solid mode under the visible light irradiation. The generation rate of CO was as high as 10.32 μmol g−1h−1, which was 5.4 and 6.4 times higher than the original Fe3O4@PPy and NiCo-LDH. The well performance might be ascribed to the generation of type Z heterojunction with the interface modifier PPy, jointly accelerating the separation and migration of photo-generated charge carriers between Fe3O4@PPy and NiCo-LDH. Besides, F@P-LDHs were also developed as supercapacitors, and their electrochemical behaviors were investigated. Their good electrochemical performances were attributed to the synergistic effect among hollow Fe3O4 microspheres, polypyrrole and NiCo-LDH. Therefore, as dual-functional materials, the hybrid materials have great potential in the field of CO2 conversion and supercapacitors.

Morphology-dependent magnetic hyperthermia characteristics of Fe3O4 nanoparticles

Magnetic hyperthermia therapy (MHT) represents an innovative approach to cancer treatment, harnessing the therapeutic capabilities of magnetic nanoparticles. Fe3O4 nanoparticles are often considered ideal candidates for MHT because of their biocompatibility. However, the clinical application of Fe3O4 nanoparticles is hindered by their low heating efficiency and concerns regarding potential toxicity linked to the high concentrations required to achieve therapeutic effects. In this study, two unique structures, hollow spherical and nanoflower Fe3O4, were successfully synthesized to enhance their magnetothermal conversion efficiency. The results indicate that Fe3O4 nanoflowers exhibit an intrinsic loss power (ILP) value of 6.52, which is 1.83 times greater than the ILP of hollow spherical Fe3O4 (3.55), indicating its enhanced potential for MHT applications. The COMSOL simulation demonstrated that higher magnetic field frequencies and intensities elevate tissue temperature and damage in tumor cells, particularly at 100 kHz and 400 kHz, with tumor tissue damage scores rising to 0.28 and 0.93, respectively. Shorter heating durations, such as 6 min, minimize harm to healthy tissue and are ideal for treatments requiring multiple sessions. After 12 min, tumor scores rose to 0.85, while normal tissue scores were 0.34, suggesting that longer durations improve therapeutic effects on tumors but also heighten the risk to healthy cells. This research provides a scientific foundation for selecting materials in the context of MHT for cancer treatment, potentially paving the way for more effective and safer therapeutic strategies.

Dual-gradient MXene/AgNWs/Hollow-Fe3O4/CNF composite films for thermal management and electromagnetic shielding applications

With the increasing prevalence of electronic devices, there is a pressing need for composite films that offer both efficient thermal management and superior electromagnetic interference (EMI) shielding. To address this, we developed a novel composite film featuring a controllable conductive-magnetic dual-gradient structure, composed of cellulose nanofibers (CNF), MXene, silver nanowires (AgNWs), and hollow ferric oxide (Fe3O4). This film was fabricated using a straightforward, cost-effective layer-by-layer vacuum filtration method. Leveraging CNF as the matrix material endows the film with remarkable flexibility. The integration of 2D MXene, 1D AgNWs, and 0D hollow Fe3O4 significantly enhances the film's thermal conductivity through multidimensional particle interactions, achieving a maximum value of 2.92 W/mK. Additionally, the dual-gradient structure of the film-comprising a transition layer and a reflection layer-improves EMI shielding efficiency by balancing high EMI shielding effectiveness with low electromagnetic wave reflection. Specifically, for the dual-gradient configuration (MAF)-25-CNF, the absorption coefficient (A) of electromagnetic waves incident on the low conductivity side reaches 0.23, and the shielding effectiveness reaches 45.8 dB. These findings highlight the potential of MXene/AgNWs/Fe3O4/CNF composite films with a controllable conductive-magnetic dual-gradient structure for applications in electronics, electrical engineering, and wearable technologies.

Construction of Hierarchically Biomimetic Iron Oxide Nanosystems for Macrophage Repolarization-Promoted Immune Checkpoint Blockade of Cancer Immunotherapy.

Cancer immunotherapy is developing as the mainstream strategy for treatment of cancer. However, the interaction between the programmed cell death protein-1 (PD-1) and the programmed death ligand 1 (PD-L1) restricts T cell proliferation, resulting in the immune escape of tumor cells. Recently, immune checkpoint inhibitor therapy has achieved clinical success in tumor treatment through blocking the PD-1/PD-L1 checkpoint pathway. However, the presence of M2 tumor-associated macrophages (TAMs) in the tumor microenvironment (TME) will inhibit antitumor immune responses and facilitate tumor growth, which can weaken the effectiveness of immune checkpoint inhibitor therapy. The repolarization of M2 TAMs into M1 TAMs can induce the immune response to secrete proinflammatory factors and active T cells to attack tumor cells. Herein, hollow iron oxide (Fe3O4) nanoparticles (NPs) were prepared for reprogramming M2 TAMs into M1 TAMs. BMS-202, a small-molecule PD-1/PD-L1 inhibitor that has a lower price, higher stability, lower immunogenicity, and higher tumor penetration ability compared with antibodies, was loaded together with pH-sensitive NaHCO3 inside hollow Fe3O4 NPs, followed by wrapping with macrophage membranes. The formed biomimetic FBN@M could produce gaseous carbon dioxide (CO2) from NaHCO3 in response to the acidic TME, breaking up the macrophage membranes to release BMS-202. A series of in vitro and in vivo assessments revealed that FBN@M could reprogram M2 TAMs into M1 TAMs and block the PD-1/PD-L1 pathway, which eventually induced T cell activation and the secretion of TNF-α and IFN-γ to kill the tumor cells. FBN@M has shown a significant immunotherapeutic efficacy for tumor treatment.

Enhanced sensing performance of flexible non-enzymatic electrochemical glucose sensors using hollow Fe3O4 nanospheres of controllable morphologies

Rapid and accurate monitoring of glucose concentration is of great significance in clinical diagnosis and treatment of diabetes and hence, it is necessary to develop glucose sensors of superior electro-catalytic capacity. Most literature utilize synergistic effect of nanocomposites to enhance glucose sensing performance, whereas it suffers from crucial restriction in physical and chemical characteristics of each constituents. Morphology of nanostructures significantly affects the electro-catalytic capacity, thus it is a novel route to improve glucose sensing performance to adjust morphology of nanostructures. Herein, we presented highly sensitive non-enzymatic electrochemical sensors for rapid and accurate glucose analysis with hollow Fe3O4 nanospheres (Fe3O4NSs) of controllable morphologies decorated on flexible fibers. The morphologies of the Fe3O4NSs were evaluated with quantitative parameters like diameter, roundness, roughness, skewness, and kurtosis acquired from SEM images and image processing algorithms, and their effect on the interfacial characteristics and the electro-catalytic capacity of the glucose sensors was investigated. Owing to the unique spherical nanostructures and superior catalysis, the Fe3O4NSs exhibit desirable solid/liquid interface for mass diffusion and abundant active sites for sufficient oxidation of glucose. Moreover, much rounder and rougher Fe3O4NSs of near Gaussian surface are readily produced at a higher Fe3+ concentration and result in favorable sensing performance. Accordingly, the optimal glucose sensor shows sensitivities of 96.1 ± 5.4 μA mM−1 cm−2 and 38.2 ± 2.2 μA mM−1 cm−2 over a preferable range of 0–18.0 mM, and a lower detection limit of 19.2 μM. Besides, the glucose sensors remain acceptable response after continuous testing for 20 times and repetitive bending for 50 times, and display superior selectivity to glucose and accurate analysis to practical samples. It is a facile and effective methodology to regulate the morphologies of the Fe3O4NSs for enhanced electro-catalytic capacity of glucose sensors.

The hollow cubic octahedral structure of Fe3O4 with excellent electromagnetic wave absorption capacity

The unique nanostructure combined with high dielectric and magnetic losses is essential for electromagnetic wave (EMW) attenuation in microwave-absorbing materials (MAM). In this paper, using cubic octahedral Cu2O as a template, we synthesized hollow cubic octahedral Fe(OH)3 at first. After annealing at 450 °C, the hollow cubic octahedral structure Fe3O4 could be obtained. When the filling ratio was 40 %, the minimum reflection loss (RLmin) reached -66.08 dB, and the maximum effective absorption bandwidth (EAB) was 5.38 GHz at a thickness of 1.84 mm, exhibiting improved EMW properties compared with previous works. The hollow cubic octahedral structure of Fe3O4 enhances EMW absorption characteristics, which is attributed to abundant dipole polarization, interface polarization, and good conduction loss. These results indicate that Fe3O4 with the hollow cubic octahedral structure can be used as potential candidates for efficient and broadband EMW absorbers.

Enhanced heating efficiency for hollow Fe3O4 spherical submicron particles

We have investigated ac hysteresis loops of hollow Fe3O4 submicron particles with variable particle size of d = 100−696 nm by micromagnetic simulations to investigate the possible application to magnetic hyperthermia. For the hollow particle with the inner/outer diameter ratio of γ = 0.5, the hysteresis loss increases with increasing d and maximizes at d ∼ 300 nm, whereas the hysteresis loss generally increases with γ, but its behavior strongly depends on d. A specific absorption rate, calculated from the loop area at the field frequency of 500 kHz, attains 560 W/g for d = 296 nm and γ = 0.5, which is comparable to that for conventional superparamagnetic nanoparticles. This enhanced specific absorption ratio for the hollow particles can be explained by strong irreversibility between vortex states with different orientation of the vortex core, i.e. along the magnetic field and ⟨111⟩ easy axes.

Glucose-Regulated Protein 78 Targeting ICG and DOX Loaded Hollow Fe3O4 Nanoparticles for Hepatocellular Carcinoma Diagnosis and Therapy.

Liver cancer is considered as the third leading cause of cancer-related deaths, with hepatocellular carcinoma (HCC) accounting for approximately 90% of liver cancers. Improving the treatment of HCC is a serious challenge today. The primary objective of this study was to construct SP94-Fe3O4@ICG&DOX nanoparticles and investigate their potential diagnosis and treatment effect benefits on HCC. Firstly, we synthesized and characterized SP94-Fe3O4@ICG&DOX nanoparticles and confirmed their in vitro release behavior, photothermal and photodynamic performance. Moreover, the in vivo imaging capability was also observed. Finally, the inhibitory effects on Hepa1-6 in vitro and in vivo were observed as well as biosafety. SP94-Fe3O4@ICG&DOX nanoparticles have a size of ~22.1 nm, with an encapsulation efficiency of 45.2% for ICG and 42.7% for DOX, showing excellent in vivo MPI and fluorescence imaging capabilities for precise tumor localization, and synergistic photo-chemotherapy (pH- and thermal-sensitive drug release) against tumors under irradiation. With the assistance of a fluorescence molecular imaging system or MPI scanner, the location and contours of the tumor were clearly visible. Under a constant laser irradiation (808 nm, 0.6 W/cm2) and a set concentration (50 µg/mL), the temperature of the solution could rapidly increase to ~45 °C, which could effectively kill the tumor cells. It could be effectively uptaken by HCC cells and significantly inhibit their proliferation under the laser irradiation (100% inhibition rate for HCC tumors). And most importantly, our nanoparticles exhibited favorable biocompatibility with normal tissues and cells. This versatile agent can serve as an intelligent and promising nanoplatform that integrates multiple accurate diagnoses, precise positioning of cancer tissue, and effective coordination with synergistic tumor photodynamic therapy.

Construction of Fe3O4/PANI composites with hollow 0D/1D structures for efficient microwave absorption

In this study, a novel microwave absorber ferric oxide/polyaniline (Fe3O4/PANI) composite was successfully fabricated with 0-dimensional (0D) hollow Fe3O4 nanospheres and 1-dimensional (1D) hollow polyaniline (PANI) nanotubes using hydrothermal treatment and chemical oxidative polymerization. The results demonstrate that the prepared Fe3O4/PANI composites exhibit remarkable microwave absorption (MA) properties. It possesses a minimum reflection loss (RLmin) of −55.03 dB and an effective absorption bandwidth (EAB) of 4.88 GHz with a thickness of 1.84 mm. When the thickness is increased to 1.88 mm, the composite achieves a maximum EAB (EABmax) of 5.16 GHz (12.84–18 GHz) and an RL of −40.47 dB. The hollow structures of Fe3O4 and PANI reduce the weight of the absorber and also enhance the synergistic loss effects, including interfacial polarization loss and multiple reflection and scattering loss, resulting in improved MA properties. The combination of hollow 0D/1D structures provides a novel approach in designing lightweight and efficient composite MA materials.

MOF-derived hierarchical hollow Fe2O3 nanobox functionalized with Ru doping for superior H2S sensing

The hierarchical Ru-Fe2O3 nanobox was prepared by a concise hydrothermal-annealing method. The resultant Ru-Fe2O3 was composed of small Fe2O3 nanoparticles with hollow and porous structures. In order to determine that Ru doping was a useful strategy to enhance the gas sensing performance of Fe2O3-based sensors, the sensing properties of all sensors were explored systematically. As a result, the sensor based on the Ru-Fe2O3 exhibited a higher response of 32.6–100 ppm of H2S at optimum temperature (200 °C), with a faster response-recovery speed (8/34 s), compared to the pure Fe2O3 sensor. In addition, the Ru-Fe2O3 sensor was able to monitor ppb amounts of H2S with high repeatability, good selectivity and excellent long-term stability. The hierarchical hollow microstructure and improved parameters (oxygen vacancy and crystal sizes) caused by the Ru doping were responsible for the enhancement of H2S sensing performance. Moreover, the sensing mechanism of Ru-Fe2O3 based sensor toward H2S has also been discussed clearly.

Hollow magnetic Fe3O4 nanospheres for excellent electromagnetic wave absorption

The construction of lightweight magnetic electromagnetic (EM) wave absorption materials is of great significance for the development of EM wave absorption materials. Herein, hollow magnetic Fe3O4 (H–Fe3O4) nanospheres were successfully prepared by hydrothermal method. Analysis of EM parameters indicates that the formation of local conductive and magnetic networks caused by H–Fe3O4 aggregation effects leads to the significantly enhancement of permittivity and permeability. In particular, the H–Fe3O4 composite with a thickness of 2.15 mm achieved the minimum reflection loss of −50.25 dB and the corresponding bandwidth (<−10 dB) was 3.4 GHz. The synergistic effects of ferromagnetic resonance and exchange resonance and polarizations leads to excellent absorption performance. The radar cross section (RCS) simulation indicated that the RCS reduction value of H–Fe3O4 composite can reach 29.8 dB m2 under the incident angle of 20°. Moreover, the metastructure design shows an ultra-wide EM wave absorption bandwidth. This work can provide ideas for the design and application of ultra-light magnetic materials.

AgNWs/Fe3O4@NC Conductive Network Hierarchical Assembly to Prepare Flexible EMI Shielding Textile.

With the rapid development of high-power electronic instruments and communication technology, efficient electromagnetic shielding materials with strong absorption of electromagnetic waves and low reflection characteristics have become the focus of the world's attention. This study designs and synthesizes N-doped carbon-coated hollow Fe3O4 nanospheres (Fe3O4@NC) by spraying Ag nanowires (AgNWs) on textiles as conductive networks. Because of the high permeability and hollow structure Fe3O4@NC, electromagnetic wave goes through a unique process of "absorption, reflection, and reabsorption" when it passes through the surface of the composite textile. In X-band (≈8.2-12.4GHz), the average electromagnetic interference shielding effectiveness (EMI SE) reaches 50.1dB, while the reflectance shielding efficiency (SER) is only 2.6dB, and the average reflectance power coefficient (R) is as low as 0.45. The composite fabric has excellent properties and provides an effective strategy for electromagnetic interference shielding based on absorption.

Integration of hierarchical magnesium silicate with polypyrrole-coated hollow Fe3O4 hybrids as a synergistic adsorbent toward efficient water treatment

Here we demonstrate the rational design and synthesis of hierarchical Fe3O4@PPy/Mgsilicate composites for applications in water treatments. Through a facile step-by-step strategy, ultrathin Mgsilicate nanosheets (NSs) are grown on polypyrrole (PPy) coated Fe3O4 NPs to achieve the hollow structured Fe3O4@PPy/Mgsilicate composites. This smart design can effectively shorten the mass transfer of molecules, increase the specific surface area, and provide more active sites for adsorption of organic pollutants. Owing to its large specific surface area, hierarchical hollow structures, and the synergistic adsorption effect between the PPy interlayer and magnesium silicate outlayer, the resulting composites exhibited excellent adsorption on Congo Red (CR) with high adsorption capacity of 540.5 mg·g-1. The separation of the composites after sorption can be easily performed with an external magnet because of the multiple Fe3O4 cores. These results indicate that the Fe3O4@PPy/Mgsilicate composites can be employed as a highly promising adsorbent in water treatment.

Boosting nitrogen adsorption for photocatalytic ammonia production via tuning electron distribution using zero valent iron as medium

Photocatalytic nitrogen reduction to ammonia plays an important role in agricultural production and now-generation hydrogen storage technology. However, the practicality is limited by low efficiency owing to the poor charge-transfer rate and slow ammonification reactions. Herein, a ternary Fe2O3-Fe-HCNS composite is reported with all-solid-state Z-scheme heterojunction, which zero valent iron (ZVI) with abundant electrons is employed as conductor between hollow g-C3N4 sphere (HCNS) and Fe2O3. ZVI facilitates photogenerated electrons transfer and changes charge distribution on the Fe2O3-Fe-HCNS surface, thus an electron-rich region is formed around HCNS, which improves N2 adsorption and ammonification reaction on the HCNS surface. Moreover, the dual interfacial electric fields are established in the heterojunction, which can promote efficient separation and migration of photo-induced electrons and holes in space, leading to the good photocatalytic performances with the higher ammonia yield (296.30 μmol g−1h−1) and apparent quantum yield (1.38%, 400 nm) in neutral electrolytes. In addition, compared with the catalyst powder, vertical carbon paper supporting Fe2O3-Fe-HCNS catalyst can reduce secondary pollution and facilitate recycling.

Controllable preparation of wrapped Fe2O3@rGO composites and their lithium ion storage performance

In this paper, reduced graphene oxides wrapped hollow Fe2O3 spheres (Fe2O3@rGO) were successfully prepared by solvothermal method. Results show that plenty of Fe-O-C bonds between reduced graphene oxides and Fe2O3 significantly improved electron transfer rate of the composite anodes, and confinement effect of reduced graphene oxides slowed the pulverization rate of Fe2O3 during charge/discharge process. As expected, wrapped structured Fe2O3@rGO anode exhibited high rate capability of 514 mA·h/g at high current of 5.0 A/g and durable cycling life over 500 cycles with a capacity of 987 mA·h/g under 0.5 A/g with a capacity retention of 81.1%. This work provides an effective strategy for the preparation of high-rate and long-life graphene composite anode materials.

A novel synthesis of hollow Fe3O4 nanorods with a high saturation magnetization

A novel approach combined Stӧber method with the hydrothermal method was developed for the synthesis of hollow Fe3O4 nanorods by using SiO2 as the template and FeOOH nanorods as the precursor. The investigation of the reaction process confirmed that, as the SiO2 outer layer was gradually dissolved and partially nitrided to Si3N4 in an alkaline hydrazine solution, FeOOH was converted to Fe3O4, resulting in a regular rod-shaped morphology with a hollow structure. The prepared hollow Fe3O4 nanorods had an average length of 430 nm and an average width of 110 nm, and exhibited a high saturation magnetization of 81.6 emu g−1.

Electromagnetic wave absorption properties of red mud-blast furnace slag based geopolymers filled with various wave-absorption materials

In this work, red mud-blast furnace slag (RM-BFS) based geopolymers with excellent electromagnetic wave absorption property is synthesized through the incorporation of wave-absorption materials. The electromagnetic absorption property of geopolymer is characterized through the arched test, in which the reflection loss of specimens is tested by vector network analyzer (VNA). The microstructure and conductivity of geopolymers are characterized through scanning electron microscopy (SEM), concrete porous structure analyzer and conductivity tester. The crystalline phase and functional groups of geopolymers are characterized by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). Compared to Portland cement concrete (PCC), wave absorption band of the geopolymer is wider and the absorption peak in high frequency band is more intense. With the optimal addition of hollow glass microsphere (HGM), Fe2O3 and graphite particles, the absorption bandwidth with reflection loss less than −5 dB are 12.4, 7.7 and 8.1 GHz, and the maximum reflection loss are −9.4, −8.4 and −8.7 dB, respectively. This study might give a clue for preparation of geopolymers with high electromagnetic wave absorption properties.