## 2 New EMI Shielding Materials: Biochars, Scaffolds, Rare Earth, and Ferrite-Based Materials
### Iron Oxide-Based Materials as EMI Shielding Material
Fe\({}_{3}\)O\({}_{4}\)-nanoparticle-loaded functionalized multi-walled carbon nanotubes were produced by [PERSON] 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). [PERSON] 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 [PERSON] 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). [PERSON] 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\({}_{\rm T}\) -3.81 dB) compared to the MoS\({}_{2}\)-rGO/Fe\({}_{3}\)O\({}_{4}\) nanocomposite (SE\({}_{\rm T}\) -8.27 dB). This was caused by interfacial polarization in the presence of an electromagnetic field. By the chemical oxidative polymerization of pyrrole, [PERSON] 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)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\({}^{3}\), [PERSON] et al. suggested a new and simple method called epoxy-water-inorganic filler suspended emulsion polymerization [127].