In ChemRxiv, January 2023, we considered the literature regarding the use of Fe3O4 nanoparticles for EMI shielding. From this work we can deduce that, besides the use of encapsulated NPs to have composites, another approach is that of mixing the precursors of magnetic nanoparticles directly in a relevant supporting material. In the ChemRxiv article, we also focused on biochar as support of NPs.