Green Synthesis and Characterization of Fe3O4 and ε-Fe2O3 Nanoparticles Using Apricot Kernel Shell Extract and Study of Their Optical Properties

The synthesis of Fe3O4 and ε-Fe2O3 nanoparticles (hereafter referred to as Fe3O4 NPs and ε-Fe2O3 NPs, respectively) was conducted in an eco-friendly manner using FeCl3·6H2O as the primary reactant. The experiment was conducted by subjecting the sample to an aqueous solution of FeCl2·4H2O at a temperature of 80 °C for a duration of 45 min, with the inclusion of apricot kernel shell extract (AKSE) as a natural reducing agent. The synthesized Fe3O4 NPs and ε-Fe2O3 NPs were characterized using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). The optical properties of Fe3O4 NPs and ε-Fe2O3 NPs were examined, with the band gap energy estimated using the Kubelka–Munk formula. The results demonstrated a band gap of Eg (Fe3O4 NPs) = 2.59 eV and Eg (ε-Fe2O3 NPs) = 2.75 eV, thereby confirming their semiconductor behavior. The photoconductivity of Fe3O4 NPs and ε-Fe2O3 NPs was analyzed as a function of photon energy. For Fe3O4 NPs, photoconductivity exhibited an increase between 1.37 eV and 6.2 eV prior to reaching a state of stability. A comparable trend was observed for ε-Fe2O3 NPs, with an increase from 1.35 eV to 6.22 eV, followed by stabilization. Furthermore, the extinction coefficient (k) was determined. For Fe3O4 NPs, k ranged from 39 to a maximum of 300, while for ε-Fe2O3 NPs, it varied from 37 to a maximum of 280. A higher k value indicates strong light absorption, rendering these nanoparticles highly suitable for photothermal and sensing applications.