Microstructures and Dielectric Permittivity Properties of Fe3O4/Cdots Nanocomposites Synthesized by Green Route Utilizing Moringa Oleifera Extract and Watermelon Peel

Abstract

Dielectric materials are beneficial for storing electrical energy due to their insulating and polarization properties in response to external electric fields. Magnetite has shown promise as a dielectric material among other materials due to its good magnetic properties, low toxicity, and biocompatibility. However, the weakness of Fe3O4, which has low stability and easy agglomeration, requires a modification on its surface by using Carbon dots (Cdots). This research investigates the dielectric properties of Fe3O4/Cdots obtained through the green synthesis method. Fe3O4 nanoparticles were synthesized using the co-precipitation method with Moringa oleifera leaf extract as a reducing and stabilizing agent. In contrast, Cdots were synthesized using the hydrothermal method with watermelon peel waste as a carbon source. The Fe3O4 composite nanoparticles were characterized using X-ray diffraction (XRD), scanning electron microscopy-energy dispersive X-ray (SEM-EDX), ultraviolet-visible spectroscopy (UV-Vis), and impedance spectroscopy. The XRD spectra revealed the existence of cubic inverse spinel and a reduction in crystal size as the concentration of Cdots increased, measuring 7.8 and 7.1 nm, respectively. SEM-EDX revealed that the sample is composed of Fe, O, and C elements and has a spherical shape with Cdots distributed on the surface of Fe3O4. The UV-Vis spectrum showed the absorption peak of Cdots at 282 nm. The Fe3O4 absorption peak is identical to the Fe3O4/Cdots absorption peak at 193 nm. The increase in band gap energy from 2.96 to 3.33 eV is related to the increase in Cdots concentration. In the 10-900 kHz frequency range, dielectric property tests demonstrated peak dielectric permittivity values (real and imaginary). A substantial decrease was observed between 10 kHz and 200 kHz, followed by a relatively stable pattern up to 900 kHz. The loss tangent value obtained has a tanδ value <0.5, which means that the addition of Cdots affects reducing the energy loss stored in Fe3O4.