Synthesis and characterization of Fe₃O₄/polypyrrole/carbon nanotube composites with tunable microwave absorption properties: Role of carbon nanotube and polypyrrole content

Two different sizes of Fe₃O₄ nanoparticles were synthesized by hydrothermal (H-Fe₃O₄, ≈100nm) and co-precipitation (C-Fe₃O₄, ≈20nm) methods. Further, Fe₃O₄/polypyrrole (Ppy) composites were prepared by polymerizing the conductive monomer, pyrrole on the surface of Fe₃O₄. In addition, we also synthesized Fe₃O₄/Ppy/carbon nanotube (CNT) composites by blending the CNTs with Fe₃O₄/Ppy composites. Epoxy resin-based microwave absorbers were prepared at different thicknesses (1, 2 and 3mm) by mixing 20% by weight of the as-prepared composites and the complex permittivity (ε'-jε″) and permeability (μ'-jμ″) were measured in the 2-18GHz frequency range. The composites exhibited significant improvement in microwave absorption (reflection loss≤-10dB) with a bandwidth from 8 to 12.5GHz (X-band) by matching the magnetic properties of Fe₃O₄ and the dielectric properties of Ppy and CNTs for 20wt% of fillers in 3-mm thickness absorbers. The addition of CNTs into H-Fe₃O₄/Ppy composites further enhances the minimum reflection loss from -15.8 to -25.9dB. The present results can pave the way to construct microwave absorbers with a desired reflection loss at a target frequency and thus, the efficient complementarities between complex permittivity and permeability of the nanocomposites can be achieved.