New Electromagnetic Interference Shielding Materials: Biochars, Scaffolds, Rare Earth, and Ferrite Based Materials

9.24.3 New Electromagnetic Interference Shielding Materials: Biochars, Scaffolds, Rare Earth, and FerriteBased Materials Dragana Marinković, Slađana Dorontić, Dejan Kepić, Kamel Haddadi, Muhammad Yasir, Blaž Nardin and Svetlana Jovanović Special Issue Advanced Nanomaterials for Electromagnetic Shielding and Absorption Applications Edited by Dr. Mingxing Piao and Dr. Yenan Song Review https://doi.org/10.3390/nano15070541 Academic Editors: Mingxing Piao and Yenan Song Received: 7 March 2025 Revised: 30 March 2025 Accepted: 31 March 2025 Published: 2 April 2025 Citation: Marinkovi´c, D.; Doronti´c, S.; Kepi´c, D.; Haddadi, K.; Yasir, M.; Nardin, B.; Jovanovi´c, S. New Electromagnetic Interference Shielding Materials: Biochars, Scaffolds, Rare Earth, and FerriteBased Materials. Nanomaterials 2025, 15, 541. https://doi.org/10.3390/ nano15070541 Copyright: © 2025 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/ licenses/by/4.0/). Review New Electromagnetic Interference Shielding Materials: Biochars, Scaffolds, Rare Earth, and Ferrite-Based Materials Dragana Marinkovi´c 1,*, Sla ¯ dana Doronti´c 1, Dejan Kepi´c 1, Kamel Haddadi 2, Muhammad Yasir 3, Blaž Nardin 4and Svetlana Jovanovi´c 1,* 1Vinˇca Institute of Nuclear Sciences, National Institute of the Republic of Serbia, University of Belgrade, P.O. Box 522, 11001 Belgrade, Serbia; [email protected] (S.D.); [email protected] (D.K.) 2University of Lille, CNRS, Centrale Lille, University Polytechnique Hauts-de-France, UMR 8520-IEMN-Institut d’Electronique de Microélectronique et de Nanotechnologie–Lille, 59650 Villeneuve-d’Ascq, France; [email protected] 3Department of Computer Science, Division of Microrobotics and Control Engineering, University of Oldenburg, Ammerländer Heerstraße 114-118, 26129 Oldenburg, Germany; [email protected] 4Faculty of Polymer Technology, Ozare 19, 2380 Slovenj Gradec, Slovenia; blaz.nar[email protected] *Correspondence: [email protected] (D.M.); [email protected] (S.J.) Abstract: In this review, a comprehensive systematic study of the research background, developments, classification, trends, and advances over the past few years in research on new electromagnetic interference (EMI) shielding materials will be described. The following groups of new materials for EMI shielding will be discussed: biochars, scaffolds, rare earth, and ferrite-based materials. We selected two novel, organic, lightweight materials (biochars and scaffolds) and compared their shielding effectiveness to inorganic materials (ferrite and rare earth materials). This article will broadly discuss the EMI shielding performance, the basic principles of EMI shielding, the preparation methods of selected materials, and their application prospects. Biochars are promising, eco-friendly, sustainable, and renewable materials that can be potentially used as a filter in polymer composites for EMI shielding, along with scaffolds. Scaffolds are new-generation, easy-to-manufacture materials with excellent EMI shielding performance. Rare earth (RE) plays an important role in developing high-performance electromagnetic wave absorption materials due to the unique electronic shell configurations and higher ionic radii of RE elements. Ferrite-based materials are often combined with other components to achieve enhanced EMI shielding, mechanical strength, and electrical and thermal conductivity. Finally, the current challenges and future outlook of new EMI shielding materials will be highlighted in the hope of obtaining guidelines for their future development and application. Keywords: EMI shielding materials; mechanisms of EMI shielding; biochars; scaffolds; rare earth; ferrite-based materials 1. Introduction The human population in urban and rural regions is exposed to non-ionizing electromagnetic fields (EMFs) due to the rapid development of telecommunication technology and digital systems for information transfer [ 1 , 2 ]. The association of the fifth generation (5G) and upcoming sixth generation (6G) will lead to the emergence of innovative applications (Internet of Things and self-driving vehicles) [ 3 , 4 ]. Wearable and portable electronics will soon become more commonly used [ 4 ]. The COVID-19 pandemic triggered the implementation of technology trends such as digital payments, telemedicine, and robotics, Nanomaterials 2025,15, 541 https://doi.org/10.3390/nano15070541 Nanomaterials 2025,15, 541 2 of 24 which use radiofrequency (RF) electromagnetic waves (EMWs) in the 100 kHz–300 GHz frequency range [ 5 ]. These technological advances caused an increase in artificial sources of EMF and resulted in the chronic exposure of people and the environment, creating electromagnetic pollution. Electromagnetic pollution is the continuous and uncontrolled exposure to electromagnetic fields from any emitting source of the EMF spectrum [ 5 ]. From 1950 to 2010, the levels of exposure to RF-EMF have increased from extremely low natural levels by about 1018 times [ 6 ]. Many studies have shown the harmful effects of EMF on human health [ 7 – 11 ] and the environment [ 12 – 15 ]. In addition to the potential health risks, the interference of EMW worsens heat accumulation, significantly shortening equipment lifespan [ 16 ]. Thus, new electromagnetic interference (EMI) shielding materials are urgently needed. The conventional EMI shielding materials are metals, carbons, ceramics, cement, conductive polymers, and associated composites. Metals and carbons are the most functional materials due to their high conductivity, while ceramics, cement, and (non-conductive) polymers are less efficient unless combined with functional components/materials [ 17 , 18 ]. Shielding barriers should meet the required dimensions and shapes at the lowest possible cost for various applications. Among the various new materials, organic materials such as graphene, carbon black, and carbon nanotubes are highly conducting, lightweight, flexible, and highly efficient EMI shielding materials. Still, their high price and the complexity of production and purification lead to high cost and limit their use. Inorganic materials, such as metal powders and metal oxides, are highly efficient EMI shielding materials due to their high electrical conductivity accompanied by magnetic permeability. Challenges in their application are associated with their high prices, chemical instability, corrosion, and heavy weight. Thus, in this review paper, we are focusing on new, suitable, low-cost organic materials—biochars and scaffolds. These organic EMI shielding materials are compared to novel inorganic shielding materials—rare earth and ferrite-based composites. By reviewing their production methods, yields, physico-chemical properties, and EMI shielding effectiveness, the future direction in the development of EMI shielding materials is estimated. According to the reviewed literature, biochars are promising, eco-friendly, sustainable, and renewable materials that can potentially be used as filters in polymer composites for EMI shielding applications in electronic devices and construction materials. Previous research showed that scaffolds are new-generation, easy-to-manufacture materials with excellent EMI shielding performance. Recently, great attention has been paid to traditional magnetic materials/alloys with excellent absorption of EMWs, but they are often limited by thickness and range of use. However, according to Snoek’s limit, where the direct current (DC) susceptibility and the cut-off frequency are constant, the permeability value decreases in the high-frequency range, which leads to an apparent decrease in magnetic loss capability [ 19 – 21 ]. Improving the permeability and magnetic loss of magnetic materials/alloys at high frequencies is crucial for obtaining good electromagnetic/microwave absorption properties [ 22 ]. It was shown that the electronic structure and well-chosen methods for designing magnetic materials/alloys can improve magnetism at high frequencies [23]. Therefore, magnetic metal oxide composites or perovskite oxides doped with rare earth element ions have been in development for the last few years due to their specific structures, interfacial polarization, multiple reflections, and excellent conducting and EMI shielding properties [24]. Nanomaterials 2025,15, 541 3 of 24 Rare earth materials are often characterized by various names, such as rare earth elements (REEs), rare earth metals (REMs), rare earth oxides, or yttrium-based rare earth material. This group represents a set of 17 chemical elements, as listed in the periodic table, from lanthanum (La) to lutetium (Lu), including 15 lanthanides and scandium (Sc) and yttrium (Y) with a tendency to occur in the same core deposits as lanthanides and exhibiting identical chemical properties [ 25 ]. In the crystal structure, REEs are most often found in the trivalent state (RE 3+ ), although the divalent state (RE 2+ ) is also possible. REEs with strong inter-electron interactions with their localized 3d and 4f electrons as well as strong coupling with magnetic materials have emerged as outstanding material dopants [ 26 ]. REEs based on neodymium (Nd), dysprosium (Dy), and samarium (Sm), due to their relatively large number of unpaired electrons in the atomic structure, possess a high remanent magnetization and coercivity value determining the stability of the remanent state. The orbital electron structure of these elements contains many unpaired electrons, which allows them to store large amounts of magnetic energy. The total magnetic moment originates from these unpaired electrons [ 27 , 28 ]. The reviewed literature revealed the growing interest in rare-earth-based materials as materials for EMI shielding applications [ 29 , 30 ]. These materials can be classified into several groups: RE-doped ferrites (RE-Fs), F 2 O 3 /Fe 3 O 4 , RE–transition metal intermetallics (RETMIs), RE oxides (REOs), RE-based alloys, RE spinels, RE-doped MoS 2 , and RE polymers. The above-mentioned groups of rare-earth-based materials will be discussed in detail throughout this manuscript. The main advantages of rare-earth-based materials over traditional EMI shielding materials are the magneto-dielectric effects and tunable dielectric properties in an electric or magnetic field. These properties make them attractive for exploring their EMI shielding applications. New nanocomposite-based foams and heterogeneous layered structures have shown outstanding EMI shielding properties. Namely, thermoplastic polyether-block-amide elastomer beads coated with Ti 3 C 2 T x showed an EMI shielding efficiency of 44 dB at 8.5–12.5 GHz [29] , microcellular aramid nanofiber/Ti 3 C 2 T x MXene foams reached a value of 64.9 dB [ 30 ], and foams based on the conductive polymer polypyrrole with Fe 3 O 4 achieved a value of 41.1 dB [ 31 ]. Combining MXenes with carbon nanotubes and silver nanowires in a layer-by-layer architecture, Zhang et al. achieved an EMI shielding efficiency of 53.1 dB in the X-band [32]. The development, classification, trends, and advancements of research on novel shielding materials in electromagnetic irradiation during the past few years will be thoroughly and methodically reviewed herein. The recent progress in the development of new-generation shielding materials based on biochars, 3D network structures (referred to as scaffolds in the following), materials with rare earth (referred to as rare-earth-based materials in the following), and ferrite materials will be described (Figure 1). This paper will comprehensively discuss the EMI shielding performance, basic principles and mechanisms, preparation methods, structure, morphology, and application prospects of these materials. Nanomaterials 2025,15, 541 4 of 24 ff ff ffi Figure 1. Schematic representation of new shielding materials based on biochars, scaffolds, rare earth, and ferrite materials discussed in this review. Part of Figure 1(lower, left part) is adapted from reference [33]. 2. New EMI Shielding Materials: Biochars, Scaffolds, Rare Earth, and Ferrite-Based Materials 2.1. Biochar as EMI Shielding Material Among conventional EMI shielding materials, metals such as Cu, Ag, Al, etc., are highly efficient EMI shielding materials due to their electrical conductivity and ability to reflect incident EMWs [ 16 ]. Regardless, the use of these metals is limited owing to their high density, inconvenient processing, and poor resistance to corrosion [ 16 ]. Recently, shielding materials have been investigated in the form of composites with plastic or metals as substrates [ 34 ]. As alternative solutions, conductive polymer-based composites, porous conductive foams, and polymers with microand nanoscale filters such as carbon material (graphite, graphene, reduced graphene oxide, carbon nanotubes), MXenes, metal nanoparticles, and nanowires have been explored due to their low mass densities, good flexibility, and stretchability [4,35]. One of the latest approaches in developing new, sustainable, and eco-friendly solutions for EMI shielding is the integration of natural, renewable carbon materials—biochars—into polymers [ 4 ]. Biochars originate from various biomass sources, such as bamboo, sugarcane, and cork. To create biochars from biomass, biomass resources are converted to carbon materials by pyrolytic processes in an oxygen-limited environment. A schematic presentation of biochar starting materials and production steps is displayed in Figure 2. After high-temperature carbonization, biochars show extraordinary hardness, excellent thermal stability, and high electrical conductivity, making them suitable fillers for polymers [ 36 ]. By combining biochars and polymers, the mechanical, physical, and electrical properties of both materials can be upgraded successfully. Nanomaterials 2025,15, 541 5 of 24 ff ff ff Figure 2. Different starting materials (Ricinus communis outer shell, bamboo, wood, apple, and quince stillage, olive tree pruning, eucalyptus) in biochar production, at various temperatures, usually in an oxygen-controlled atmosphere, lead to the production of porous materials with domains with graphene and amorphous carbon. The electrical conductivity of biochar is closely related to the source properties and carbonization conditions [ 37 ]. Nevertheless, some researchers have disregarded the electrical properties of biochars, so their potential application in EMI shielding has rarely been examined [38–40]. In 2018, Li et al. conducted an initial research study [ 39 ]. Namely, they used commercially available bamboo charcoal as the biochar filler and/or an ultra-high-molecular-weight polyethylene (UHMWPE)/linear low-density polyethylene (LLDPE) blend as a potential EMI shielding composite. The composite with 80 wt.% of biochar was fabricated using the mass-producing extrusion and hot compression methods. Through the carbonization of bamboo charcoal at 1100 ◦ C, a graphitic-like structure with good electrical conductivity and a high specific surface area was obtained. Namely, an electrical conductivity of 107.6 S/m and EMI shielding effectivity (SE) of 48.7 dB were measured at 1.5 GHz. The specific EMI SE of the composite was 39.0 dB cm 3 /g. This value is four times higher than the specific EMI SE of copper (10.0 dB cm3/g) [41]. Tolvanen et al. applied the same approach to prepare a biodegradable twoand threephase composite of graphite, biochar derived from pine chips, and polylactic acid (PLA) [ 4 ]. The EMI shielding performances were tested in the K-band (18–26.5 GHz). The composite showed an outstanding EMI SE of >32 dB when the materials were prepared in the form of a film with a thickness of 25 µ m and a high specific shielding effectiveness (SSE/t) of >890 dB cm 2 /g. It can be seen that these composites are convenient for the application of wearable/portable and stationary devices. Shortly after, Akgül et al. presented a biochar–iron (BC-Fe) material obtained by the pyrolysis of industrial tea waste biomass and the encapsulation of BC-Fe into polymethyl methacrylate (PMMA) polymer [ 42 ]. During synthesis, Fe(III) ions promoted the graphiti- Nanomaterials 2025,15, 541 6 of 24 zation of the amorphous carbon in biomass and contributed to biochar surface stabilization. The results of EMI SE measurements showed that the reflection component of the EMI SE of pure PMMA was near − 10 dB at frequencies of 7.8 and 10.1 GHz, while it was reduced by ~60% when the content of BC-Fe in the polymer was 40 wt.% in the frequency range of 8.5–12.9 GHz. Liang et al. successfully developed a mortar/brick structure using wood-derived porous carbon (WPC) as a skeleton and conductive 3D MXene aerogel [ 1 ]. The MXene aerogel/WPC composite was composed of highly ordered honeycomb cells inside WPC as a microreactor. Herein, a high graphitization level of natural wood was achieved by applying a high carbonization temperature of 1500 ◦ C. The MXene aerogel/WPC composite showed an excellent EMI SE value of 71.3 dB in a frequency range of between 8.5 GHz and 12.5 GHz, while the sample density was only 0.197 g/cm 3 . In the study, a wall-like mortar brick structure (WPC as mortar and MXene aerogel as brick) solved the instability of the MXene aerogel network as well as prolonged the transmission path of EM waves, dissipating the incident EM waves in the form of heat and electrical energy. The material’s superior EMI shielding performance was achieved thanks to a specific design. The shielding efficiency of a gypsum–biochar drywall-like composite was investigated by Natalio et al. [ 43 ]. They used wooden chips and eucalyptus biochar and combined them with gypsum. An enhancement in the shielding efficiency was recorded with an increased biochar content in the composites. Namely, the EMI SE values of the drywall-like plates with 10%, 20%, and 40% w/wbiochar contents were 11.65 ± 1.6, 19.2 ± 5.7, and 19.25 ±1.8 dB at a frequency of 6 GHz. This investigation contributes to expanding innovative bio-based sustainable materials with EM shielding properties in the microwave region. Savi et al. used sewage sludge to obtain biochar and investigated its EMI-shielding features [ 44 , 45 ]. The biochar was mixed with epoxy polymer (20 wt%) and cast into a film 4 mm thick. The composite showed a promising EMI SE of − 10 dB [ 44 ]. Savi et al. reported an outstanding electrical conductivity of 300 S/m [ 44 ]. The same group compared the EMI SE properties of biochar produced from carbonized sludge with graphene nanoplatelets [ 46 ]. Herein, the authors produced polymer composites with polyvinylidene fluoride (PVDF), while fillers (biochar and graphene) were added at 90 wt%. The biochar–PVDF composite showed transmission scattering of less than −30 dB. Savi et al. also studied commercial biochar produced from wood biomass to coat several layers of common building components, such as drywall panels [ 47 ]. They recorded EMI SE values of 17 dB at 1 GHz and 25 dB at 18 GHz. Drywall panels coated with several layers of biochar are easy to fabricate and a low-cost solution to realize a protected surrounding for healthcare applications (chemotherapy and tomography) to minimize the intensity of the EM field close to electronic equipment. The same research group produced a cement-based composite with commercial lignin-based biochar and polyvinyl chloride (PVC) [ 48 ]. They introduced biochar powder into cement paste to improve its shielding properties. PVC, which was used as a filler, was obtained by decommissioning old electrical cables that would have ended up in a landfill. A combination of 10 wt.% biochar and 6 wt.% PVC revealed the best shielding capacity, around 16 dB in the 5.4–8 GHz frequency range. This investigation shows great importance in the EMI shielding application and from the aspect of the circular economy. Miao et al. fabricated a conductive EBC@CNF@MWCNT composite aerogel by the freeze-drying process, mixing ferrite chloride with electrically conductive bamboo charcoal (EBC), with cellulose nanofibrils (CNFs) as a skeleton and multi-walled carbon nanotubes (MWCNTs) as a conductive enhancer in the freeze-drying process [ 36 ]. Afterward, the aerogel was soaked with polydimethylsiloxane and hot-pressed into the membrane. In the composite, EBC and MWCNTs were arranged uniformly in the CNF skeleton to form a 3D Nanomaterials 2025,15, 541 7 of 24 conducting network. The composite displayed exceptional electrical conductivity (47 S/m) and a high EMI shielding effectiveness of 39.5 dB, with an adsorption loss of ~75%. Recently, Nikolopoulus et al. used biochar prepared from olive tree pruning to fabricate composite samples with carbon black and polytetrafluoroethylene as binders [ 49 ]. The EMI shielding capacity was measured in the 1–3 GHz frequency range. The results demonstrated that the raw pure biochar had a low EMI SE, between 1.5 and 4 dB, which was enhanced with an increase in the thickness from 0.1 to 0.5 mm. On the contrary, the composite significantly improved the EMI SE, reaching a value of 39 dB. This work indicates that biochar could be used as a basis for developing composites with high EMI SE values. Milenkovic et al. recently reported that agricultural biowaste collected after apple and quince processing could be converted into EMI shielding material [ 50 ]. The starting materials were chopped, homogenized, dried, and mixed with an equal mass of KOH. The mixtures were carbonized at 850 ◦ C, under nitrogen flow. The resulting biochars were mixed with sodium silicate at 40 wt.%. The film of only 0.2 mm thickness showed an EMI SE of 15.5 dB in the 8–12 GHz frequency range. Although moderate EMI SE values were found, the study demonstrates the outstanding potential of selected biowaste in the production of sustainable EMI shielding materials. Another study by Perumal et al. proposed a new organic waste for biochar production [ 37 ]. Within the study, the composite built from Ricinus communis outer shell-based biochar and epoxy was fabricated by slow pyrolysis at 400–700 ◦ C. The results showed that the biochar pyrolysis at 700 ◦ C led to a maximal electrical conductivity of 95 S/m due to the presence of graphitic carbon. A maximum EMI SE of 26.5 dB was found in the X-band frequency range, at 40 wt.% biochar to epoxy matrix. According to the reviewed literature, biochar is a promising, eco-friendly, sustainable, and renewable material that could be used as a filter for EMI shielding applications in electronic devices and construction materials. The biochar shielding effectiveness is associated with the electrically conductive graphene region in biochars and porous structure [ 50 ]. Namely, EMW attenuation is the result of wave reflection from the graphene region and multiple reflections inside the pores. Biochar features rely on two main factors: (1) The experimental conditions (temperature, duration of heating, addition of chemical agent for pore formation or activitvation of graphitization, selected gas); (2) The starting material’s chemical composition [39]. With an increased temperature, the porosity, specific free space, and carbon content increase too, while the selection of source materials affects both the properties and yields of the resulting biochar [39]. 2.2. Scaffolds as EMI Shielding Material Many structural patterns, including highly porous materials and conductive structures such as multilayer composites obtained by stacking cellulose nanofibers/reduced graphene oxide (rGO), rGO films, and multistage composite foams, are recognized as excellent EMI shielding materials. These structures are obtained using vacuum-assisted filtration, freeze-drying techniques, or electroless deposition [ 51 ]. The mentioned procedures allow for a reduction in the reflection coefficient, but they are complex and often not reliable. The innovative manufacturing technologies imply 3D network structures (scaffolds) that can be decorated with metal nanoparticles [ 52 ], coated by polymers, encapsulated with paraffin [ 53 ], etc. These approaches enable design freedom, flexibility, precise control over the shape and size, and the connectivity of porous structures. Cellulose scaffolds (CSs) are recognized as a promising material for EMI shielding applications due to the ability of cellulose nanofibers to improve the thermal and mechanical features of nanocomposites. Tran et al. represented a 3D network structure of cellulose Nanomaterials 2025,15, 541 8 of 24 scaffolds decorated with silver nanoparticles (AgNPs) [ 52 ]. The scaffolds were filtered at the epoxy matrix and cured at 40 ◦ C to fix the nanoparticles. The obtained composite possesses a thermal conductivity of 2.52 W/m/K, which is over 11-fold the thermal conductivity of pure epoxy. The extremely high electrical conductivity of 53.691 S/m caused a remarkable SE value of 69.1 dB. He et al. designed a scaffold connected with metal nanoparticles [ 53 ]. In this work, the shape-stable composite was composed of a paraffin impregnated in a biological porous carbon scaffold, followed by a coating with polyurethane and Fe 3 O 4 nanoparticles. The biological porous carbon was obtained from a loofah sponge by immersion in a phenolic resin solution followed by carbonization. Scanning electron microscopy (SEM) results revealed that the system kept its original shape with a 3D and honeycomb-like porous structure of single fibers after carbonization. The polyurethane coating provided adequate mechanical support and effective leak-proof performance. The produced framework shows strong EMI shielding performance (up to 32 dB). Another study based on the encapsulation of Fe 3 O 4 nanoparticles in carbon scaffolds was conducted by Wei et al. [ 54 ]. Herein, laminar cellulose-paper-based scaffolds with bidirectional gradient distributed Fe 3 O 4 nanoparticles were constructed via immersion, drying, and carbonization processes. The resulting carbon scaffolds exhibited high in-plane electrical conductivity (96.3 S/m) and high shielding efficiency (1805.9 dB/cm2g). A 3D cellulose scaffold was combined with a CNT/MXene composite [ 55 ]. Nanosheets of the composite were inserted into a cellulose scaffold by vacuum impregnation. Finally, a hydrophobic and multifunctional 3D system was produced by wrapping it with poly (dimethylsiloxane). The composite had a high compressive strength of 1.53 MPa, a maximum strain at fracture of 74.1%, and an outstanding SE (29.3 dB). Hu et al. reported a dual-ice templating assembly strategy to prepare a dualinterpenetrated scaffold [ 56 ]. The scaffold was linked with a high-quality graphene array and porous MXene-Co aerogel. It showed an absorption-dominated EMI SE of 72.86 dB. Three-dimensional-printing technology was applied for scaffold fabrication based on a triply periodic minimal surface and 70% porosity [ 42 ]. The monolithic layered dipping method was used to regulate the gradient distribution of carbon nanotubes on the 3Dprinted scaffold surface and ensure integrity. This system blocked 99.9% of EM waves. The value of the SE in this case was 35.9 dB. Previous research showed that scaffolds are new-generation, easy-to-manufacture materials with excellent EMI shielding performance. Due to their exceptional threedimensional construction and inner network, they show anisotropic thermal conductivity and allow heat dissipation, making them efficient EMI shielding materials [ 52 , 56 ]. The results from the literature based on biochar and scaffolds in shielding applications are listed in Table 1. Table 1. Summarized results for biochar and scaffolds as EMI shielding materials. Material Reinforcement and Matrix Thickness EMI Shielding Effectiveness Frequency Bamboo charcoal/HMWPE/LLDPE composite 3 mm, 140 mm 48.7 dB 1500 MHz [39] Pine chip/PLA composite 0.25 mm >32 dB 18–26.5 GHz [4] MXene aerogel/WPC composite 3 mm 71.3 dB 8.5–12.5 GHz [1] Gypsum–biochar drywall-like composite >2 mm 11.65 ±1.6 dB, 19.2 ±5.7 dB, and 19.25 ±1.8 dB for 10, 20, and 40% w/w biochar contents 6 GHz [43] Nanomaterials 2025,15, 541 15 of 24 prepare α -Fe 2 O 3 are thermal decomposition and precipitation in the liquid phase. The β -phase of Fe 2 O 3 is metastable, and at temperatures above 773 K, it converts to the α -phase. It can be obtained by the thermal decomposition of iron (III) salts. Similar to the β -phase, γ -Fe 2 O 3 is also metastable and converts to the α -phase at high temperatures [ 114 ]. It has a cubic structure, and in the bulk form, it is ferromagnetic, but γ -Fe 2 O 3 nanoparticles less than 10 nm in size show superparamagnetic behavior. The methods of γ -Fe 2 O 3 preparation involve the thermal dehydration of gamma iron (III) oxide-hydroxide, the modest oxidation of Fe3O4 , or the thermal decomposition of suitable iron salts [ 115 ]. The ε -phase is rhombic with properties between those of the alpha and gamma phases. It is metastable with a tendency to transform to the alpha phase at temperatures of between 773 and 1000 K. The synthesis of pure ε -Fe 2 O 3 is challenging and involves the oxidation of iron in an electric arc or sol–gel precipitation from iron (III) nitrate [ 116 ]. In addition, an amorphous form of Fe2O3also exists, which can be prepared under high pressure. Oxides of iron have become interesting candidates for electromagnetic interference (EMI) shielding due to several factors. Fe 2 O 3 is a magnetic material, while Fe 3 O 4 is a ferromagnetic. Magnetic materials can interact with and absorb electromagnetic waves, especially at lower frequencies (like radio waves), thus reducing EMI. Iron oxides exhibit a certain level of electrical conductivity, allowing them to contribute to EMI shielding by reflecting or absorbing the electrical components of electromagnetic waves. In addition, they can contribute to the absorption of electromagnetic energy through dielectric loss, a mechanism that involves converting electromagnetic energy into heat. This makes it effective in dissipating energy and preventing the transmission of EMI. Finally, iron oxides are abundant, inexpensive, and easy to combine in composite materials, such as polymers or carbon-based materials, and can maintain their properties over time. For EMI shielding applications, iron oxides are often combined with other materials, such as various polymers, graphene oxide, carbon nanotubes, or similar, to achieve desirable EMI shielding, mechanical strength, and electrical and thermal conductivity. Using an in situ polymerization technique, Azadmanjiri et al. created iron oxide and polypyrrole nanocomposites and examined their EMI shielding properties in the 0.1–18 GHz frequency range [ 117 ]. The composites’ intimate contact between the conducting and magnetic phases increased absorption by 10.10 dB at the instrument’s highest frequency limit (17–18 GHz), while iron oxide nanoparticles only increased the absorption by 2.6 dB. As the possible cause of this improvement, they proposed a better match between dielectric loss, magnetic loss, and improved dispersion of the magnetic/conductive nanocomposites in the matrix. Gupta et al. [ 118 ] reported that the microwave shielding properties were affected by the various morphologies of iron oxides. Using a two-step sol–gel process, they produced various ferrite structures, including cubes, rods, and flakes, covered with multilayer rGO. Their EMI shielding capabilities were evaluated in the Ku-band frequency range. In comparison to the flakeand cube-shaped iron oxides, the rod-shaped iron oxide covered with rGO sheets had the highest shielding efficiency value of ~33.30 dB (>99.9% attenuation). This resulted from the combined effect of magnetic and dielectric losses. Anisotropy energy in the composites, eddy current effects, and natural resonances were the sources of magnetic loss. The nanoferrite particle content of the composite was the main cause of eddy currents in the microwave ranges. The surface anisotropic field would result in higher anisotropy energy for the small materials due to the small-size effect. The higher anisotropy energy also contributed to greater microwave absorption. Moreover, the magnetic iron oxide was coated with an rGO layer, which increased the interfaces and surface polarization charges. Interfacial polarization is a significant polarization process, and the corresponding relaxation will lead to a loss mechanism. One of the main causes of dielectric loss could be Nanomaterials 2025,15, 541 16 of 24 interfacial polarization. It is well known that some heating-induced absorption losses are caused by the interaction of surface-formed molecular dipoles with the microwave field. Dhawan et al. created a conducting ferrimagnetic PANI nanocomposite implanted with titanium dioxide (70–90 nm) and γ -Fe 2 O 3 (9–12 nm) nanoparticles using microemulsion polymerization [ 119 ]. They discovered that the high shielding effectiveness value of − 45 dB owing to absorption (SE A ) was caused by dielectric and magnetic losses that resulted from the combined action of γ -Fe 2 O 3 and TiO 2 . In contrast, the SE A of PANITiO 2 was around 22.4 dB, but that of PANIγ -Fe 2 O 3 was approximately 8.8 dB. In another work, PANI tubes made of rGO coated with γ -Fe 2 O 3 nanoparticles were synthesized and characterized by Singh et al. [ 120 ]. The intercalated iron oxide nanoparticles were produced by thermally breaking down ferric acetyl acetonate in a reducing atmosphere. The β -naphthalene sulphonic acid-induced oxidative polymerization of aniline, which produced the core–shell shape, was also used to enclose those nanoparticles. At a thickness of 2.5 mm, the presence of rGOγ -Fe 2 O 3 in the PANI core structures increased the composite’s interfacial polarization and effective anisotropy energy, which increased scattering and produced a high shielding efficiency of about 51 dB. Iron oxides are frequently combined with different carbon nanomaterials. The composite material can effectively absorb, reflect, and dissipate electromagnetic radiation over a wider frequency range by fusing the electrical conductivity of carbon nanotubes with the magnetic qualities of iron oxides. Fe 3 O 4 -nanoparticle-loaded functionalized multi-walled carbon nanotubes were produced by Bhaskara Rao et al. [ 121 ]. They discovered a high overall specific shielding efficiency of around 49.56 dB/(g cm −3 ), along with improved absorption (15.85 dB) and reflection (9.43 dB). Liu et al. [ 122 ] developed trilayer-type laminated nanocomposites with a matching layer of 15 wt.% Fe 3 O 4 , an absorbent layer of 5 wt.% MWCNTs, and a reflecting layer of 10 wt.% MWCNTs. Their results showed that such trilayer-type laminated nanocomposites have an excellent ability to absorb microwaves up to 40 dB in the 13 GHz to 40 GHz frequency range. Ferroferric oxide (Fe 3 O 4 ) and MWCNTs were integrated by Li et al. into a core–shell system made of high-density polyethylene (HDPE), polyvinylidene fluoride (PVDF), and polystyrene (PS) [ 123 ]. The composite with MWCNTs in the PS shell and Fe 3 O 4 in the PVDF matrix had the highest SE, measuring 25 dB at 9.5 GHz with 1 vol.% Fe 3 O 4 and 1 vol.% MWCNTs. The SE was over 20 dB throughout the tested frequency range (X-band). Prasad et al. [ 124 ] developed a facile two-step hydrothermal process for the synthesis of a MoS 2 –reduced graphene oxide/Fe 3 O 4 (MoS 2 -rGO/Fe 3 O 4 ) nanocomposite and its application as an enhanced shielding material against electromagnetic interference. The Fe 3 O 4 nanoparticles were spherical and evenly distributed throughout the MoS 2 -rGO composite. The MoS 2 -rGO/Fe 3 O 4 nanocomposite was found to be an extremely effective electromagnetic shielding material in the 8.0–12.0 GHz X-band, according to an examination of its electromagnetic shielding efficiency. The MoS 2 -rGO composite showed low shielding performance (SE T ~3.81 dB) compared to the MoS 2 -rGO/Fe 3 O 4 nanocomposite (SE T ~8.27 dB). This was caused by interfacial polarization in the presence of an electromagnetic field. By the chemical oxidative polymerization of pyrrole, Sambyal et al. created a conducting polymer-based composite encapsulated with barium strontium titanate (BST), rGO, and Fe 3 O 4 nanoparticles [ 125 ]. Filler components in the conducting polymer matrix produced an absorption-dominated shielding efficiency value of 48 dB in the 8.2–12.4 GHz (X-band) frequency range. Furthermore, the chemical and thermal stability of the composite material was enhanced by the use of magnetic and dielectric fillers. By using a self-assembly process, rGO was also added to latex coupled with magnetic iron oxide (Fe 3 O 4 ) and flexible natural rubber [ 126 ]. Compared to NRG composites, Fe 3 O 4 enhanced the electromagnetic interference shielding effectiveness (EMI SE) of natural rubber/reduced graphene oxide (NRG) Nanomaterials 2025,15, 541 17 of 24 composites. The EMI SE value of the NRMG composite with 10 parts per 100 parts of rubber rGO is 1.4 times higher than that of the NRG composite with the same rGO content in the 8.2–12.4 GHz frequency band. With a specific EMI SE of 26.4 dB mm −1 , the NRMG composite outperforms the previously reported polymer/Fe 3 O 4 @rGO composites with a low rGO concentration. Remarkably, the NRMG composite’s EMI SE only decreases by 3.5% after 2000 bending–release cycles, indicating that it may find application in flexible shielding materials. In order to create 3D network porous graphene nanoplatelet (GNP)/Fe 3 O 4 /epoxy nanocomposites with a low density of 0.34–0.73 g/cm 3 , Liu et al. suggested a new and simple method called epoxy–water–inorganic filler suspended emulsion polymerization [ 127 ]. The porous nanocomposite that resulted from loading 7 wt.% graphene nanoplatelets and 7 wt.% Fe 3 O 4 nanoparticles showed a satisfactory specific electromagnetic interference (EMI) shielding effectiveness of about 37.03 dB/(g/cm 3 ), which was much higher than that of the solid equivalents (28.30 dB/(g/cm 3 )). In another study, Fe 3 O 4 /thermally annealed graphene aerogel (Fe 3 O 4 /TAGA) was created by first thermally annealing ethylenediaminefunctionalized Fe 3 O 4 (NH 2 -Fe 3 O 4 ) nanoparticles with graphene oxide (GO), followed by the addition of l-ascorbic acid [ 128 ]. Then, the Fe 3 O 4 /TAGA/epoxy nanocomposites were created using a template-casting technique. The resulting Fe 3 O 4 /TAGA/epoxy nanocomposites achieved the highest electromagnetic interference shielding effectiveness (EMI SE of 35 dB in the X-band) when the mass ratio of GO to NH2-Fe3O4was 2:1 and the total mass fraction of Fe 3 O 4 /TAGA was 2.7 wt.% (comprising 1.5/1.2 wt.% Fe 3 O 4 /TAGA). This was significantly better than epoxy nanocomposites with the same Fe3O4/thermally annealed graphene oxide (Fe3O4/TAGO) loading, which only showed an EMI SE of 10 dB. Liu et al. created magnetic reduced graphene oxide rGO@Fe 3 O 4 nanoplatelets (NPs), which were used as fillers, by co-precipitation and electrostatic self-assembly [ 129 ]. The nanocomposites were made by applying external magnetic fields to align rGO@Fe 3 O 4 NPs during epoxy curing. Because of the anisotropic properties of rGO@Fe 3 O 4 NPs and external magnetic fields, the nanocomposite containing aligned rGO@Fe 3 O 4 NPs showed anisotropic thermal conductivity. The produced sample exhibited exceptional thermal stability and 13.45 dB EMI shielding at 8.2 GHz. Overall, the rGO@Fe 3 O 4 NPs’ in-plane interaction was enhanced by aligning them under a magnetic field, which promoted the growth of horizontal thermal conductive networks. Reflection is the main EMI shielding mechanism. Three-dimensional Fe 3 O 4 -decorated carbon nanotube/reduced graphene oxide foam/epoxy (3D Fe 3 O 4 -CNT/rGF/EP) nanocomposites with highly aligned threedimensional structures were created by Liang et al. using a simple template approach [ 130 ]. The obtained 3D Fe 3 O 4 -CNT/rGF/EP nanocomposites with 0.24 wt.% rGF and 2.76 wt.% Fe 3 O 4 -CNTs showed a remarkable electrical conductivity of 15.3 S/m and an EMI SE of 36 dB within the X-band range, which was a nearly 482% improvement when compared to the EMI SE value of physically blended Fe 3 O 4 -CNT/EP nanocomposites without a three-dimensional structure (~6 dB). Using a supercritical carbon dioxide (Sc-CO 2 ) foaming technique, lightweight and flexible methyl vinyl silicone rubber (VMQ)/multi-walled carbon nanotube (MWCNT)/ferriferrous oxide (Fe 3 O 4 ) nanocomposite foams with superior EMI shielding capabilities were created [ 131 ]. The addition of a cellular structure and magnetic Fe 3 O 4 nanoparticles greatly improved the VMQ/MWCNT/Fe 3 O 4 foams’ microwave-absorbing capacity by successfully lowering secondary electromagnetic wave interference brought on by reflection. In the 8.2–12.4 GHz frequency range, these nanocomposite foams, which have an approximate density of 0.48 g/cm 3 , showed an EMI shielding efficiency (SE) of 27.5 dB and an average absorption ratio of up to 64%. The foams had a specific EMI SE of about 72 dB g −1 cm 3 and a high conductivity of about 14.6 S/m with a filler loading of 1.78 vol.%. Nanomaterials 2025,15, 541 18 of 24 Shu et al. [ 132 ] used rice-husk-based activated carbon (AC) and produced composites with acicular or octahedral Fe 3 O 4 nanoparticles. A significant effect on the EMI shielding effectiveness of the composites was assigned to the morphology of the metallic nanoparticles and the layered structure of the C component of the composites. They achieved an EMI SE of −52.14 dB. Record values of EMI shielding effectiveness were achieved for MXene by incorporating magnetic nanoparticles as intercalators between layers [ 133 ] and 3D N-doped GO with silver nanowires (−79.99 dB) at a thickness of 2.660 mm [134]. 3. Conclusions This review has provided a comprehensive overview of the developments, classification, trends, and advances in new electromagnetic shielding materials. It gives a thorough literature review of the EMI shielding properties of new EMI shielding materials such as biochars, scaffolds, rare earth, and ferrite-based materials. A detailed discussion is given regarding the preparation methods, structure, EMI shielding performance, EMI shielding mechanisms, and application perspectives of these materials. Looking ahead, the prospects for and research on electromagnetic shielding materials should focus on scalability, improving performance, cost-effectiveness, sustainability, versatility, and production methods to advance new materials like biochars, scaffolds, rare earth, and ferrite-based materials as novel EMI shielding solutions. Biochars are promising eco-friendly, sustainable, and renewable materials that can be potentially used as EMI shielding materials in electronic devices and construction materials, similar to scaffolds, new-generation, easy-to-manufacture materials with excellent EMI shielding performance. Although MXene, carbon nanotubes, and graphene-based composites are highly efficient EMI shielding materials due to their large free surface area, high aspect ratio, chemical stability, and lightweight nature, the large number of synthetic phases leads to their high price. Carbon-based nanomaterials derived from biomass are being developed in a quest for new, cost-efficient, sustainable, and affordable materials. The current disadvantages of these materials are the thickness of the shielding barrier and lack of transparency, which limit some applications. Materials doped with rare earth elements have been developing over the last few years. They have specific structures, interfacial polarization, multiple reflections, and excellent conductive and EMI shielding properties. Combining the magnetic properties of ferrite-based materials with the electrical conductivity of carbon nanomaterials, composite materials can efficiently absorb, reflect, and dissipate electromagnetic energy across a broader frequency range. Although the materials showed outstanding EMI shielding performance, the price of REEs will limit the application of these composites to more sophisticated and sensitive fields such as medicine. Their EMI shielding effectiveness, good magnetic and dielectric properties, excellent thermal stability, and high electrical conductivity and mechanical strength make biochars, scaffolds, rare earth, and ferrite-based materials ecological and sustainable solutions as new products for blocking EMWs. Author Contributions: Conceptualization, S.J. and D.M.; validation, S.D., M.Y., K.H., B.N. and D.K.; resources, S.J. and M.Y.; writing—original draft preparation, S.J., S.D., D.K., M.Y., K.H., B.N. and D.M.; writing—review and editing, S.J., M.Y. and D.M.; supervision, S.J., M.Y., K.H., B.N. and D.M.; project administration, S.J.; funding acquisition, S.J. All authors have read and agreed to the published version of the manuscript. Funding: This research was supported by the European Union’s Horizon Europe Coordination and Support Actions Programme under grant agreement No 101079151-GrInShield. S.J., S.D., D.K., and Nanomaterials 2025,15, 541 19 of 24 D.M. thank the Ministry of Science, Technological Development and Innovation of the Republic of Serbia (grant number 451-03-136/2025-03/200017). Data Availability Statement: This review article does not contain any original data. All data referenced in this article are publicly available from the sources cited in the references. No new datasets were generated or analyzed in this work. Conflicts of Interest: The authors declare no conflicts of interest. References 1. Liang, C.; Qiu, H.; Song, P.; Shi, X.; Kong, J.; Gu, J. Ultra-light MXene aerogel/wood-derived porous carbon composites with wall-like “mortar/brick” structures for electromagnetic interference shielding. Sci. Bull. 2020,65, 616–622. [CrossRef] 2. Li, J.; Cui, M.; Wen, J.; Chen, Y.; Shi, B.; Fan, H.; Xiang, J. Leather-like hierarchical porous composites with outstanding electromagnetic interference shielding effectiveness and durability. Compos. 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