Influence of pH and annealing temperature on hematite (α-Fe2O3) nanoparticle synthesis with pine needle extract and investigation of structural, magnetic, and dielectric properties

Abstract

This study used pine needle extract, a green method, to synthesize hematite-phase iron oxide nanoparticles. The structural, magnetic, and dielectric properties of the hematite nanoparticles synthesized at varying pH, or potential hydrogen, conditions and subjected to different annealing temperatures were examined. X-ray diffraction (XRD) was used to confirm the hexagonal hematite crystalline structure and demonstrated a significant variation in crystallite size from 7.28 to 27.36 nm at 500 °C and from 43 to 46 nm at 750 °C for different pH values. Fourier transform infrared spectroscopy (FTIR) indicated the presence of two absorption bands at 465–475 cm⁻¹ and 551–559 cm⁻¹ associated with the bending and stretching of Fe–O. UV–Vis DRS exhibited semiconducting properties, with allowed direct and indirect band gaps reducing from roughly 2.05−2.25 eV at 500 °C to 1.29−1.88 eV at 750 °C, implying a quantum confinement effect. The influence of pH and annealing temperature on the magnetic properties of hematite nanoparticles was also studied with a vibrating sample magnetometer (VSM), revealing variations in saturation magnetization, residual magnetization, and coercivity force. An LCR meter was used to analyze the frequency dependence of the real and imaginary components of the permittivity, dielectric loss tangent, and AC conductivity. The results highlight that synthesis issues, especially pH and annealing temperature, are crucial in modulating the physicochemical features of hematite nanoparticles.