In this study, a simple, rapid, and eco-friendly green method was introduced to synthesize magnetite nanoparticles (Fe3O4-NPs) successfully. Seaweed Kappaphycus alvarezii (K. alvarezii) was employed as a green reducing and stabilizing agents. The synthesized Fe3O4-NPs were characterized with X-ray diffraction (XRD), ultraviolet-visible spectroscopy (UV-Vis), Fourier transform infrared (FT-IR), and transmission electron microscopy (TEM) techniques. The X-ray diffraction planes at (220), (311), (400), (422), (511), (440), and (533) were corresponding to the standard Fe3O4 patterns, which showed the high purity and crystallinity of Fe3O4-NPs had been synthesized. Based on FT-IR analysis, two characteristic absorption peaks were observed at 556 and 423 cm−1, which proved the existence of Fe3O4 in the prepared nanoparticles. TEM image displayed the synthesized Fe3O4-NPs were mostly in spherical shape with an average size of 14.7 nm.

The complex permittivity, permeability and electromagnetic (EM) wave absorption properties have been investigated for resin compacts containing 75 wt% composite powders of α-Fe/C(a) and Fe2B/C(a). The real and imaginary parts ( and εr′) of relative permittivity for the resin composites remained almost constant in the 0.05–20.05 GHz range. The imaginary part of the relative permeability (μr′) exhibited a wide peak in the 1–9 GHz range for α-Fe/C(a) and in the 2–18 GHz range for Fe2B/C(a). Both resin composites exhibited good EM wave absorption properties (RL < −20 dB) in the 4.4–8.3 GHz range with an absorber thickness of 1.9–3.4 mm, and in the 7.5–16 GHz range for an absorber thickness of 1.2–2.2 mm, respectively.

The synthesis of gold nanoparticles (Au-NPs) is performed by the reduction of aqueous gold metal ions in contact with the aqueous peel extract of plant, Garcinia mangostana (G. mangostana). An absorption peak of the gold nanoparticles is observed at the range of 540-550 nm using UV-visible spectroscopy. All the diffraction peaks at 2 = 38.48 ∘ , 44.85 ∘ , 66.05 ∘ , and 78.00 ∘ that index to (111), (200), (220), and (311) planes confirm the successful synthesis of Au-NPs. Mostly spherical shape particles with size range of 32.96 ± 5.25 nm are measured using transmission electron microscopy (TEM). From the FTIR results, the peaks obtained are closely related to phenols, flavonoids, benzophenones, and anthocyanins which suggest that they may act as the reducing agent. This method is environmentally safe without the usage of synthetic materials which is highly potential in biomedical applications.

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