Structure, optical, magnetic, morphology and dielectric studies of pristine and green synthesized hematite nanoparticles

The present study describes the green synthesis of hematite (α-Fe₂O₃) nanomaterials using the Tabernaemontana divaricata flower extract as a reducing/capping/stabilizing agent and the changes observed in the structural, optical, magnetic and dielectric properties of the product with respect to the pristine counterpart. Powder XRD study showed that use of the extract in green synthesis produces hematite nanomaterials of reduced size, whereas FE-SEM, HRTEM and EDX studies revealed the morphology, particle size distribution, crystallinity as well as the elemental contributions. FT-IR spectroscopy detected the different functional groups and metal-ion bonding present in the synthesized nanomaterials. Raman study observed the seven Raman active (two A_1g and five E_g) modes with different intensities. From the UV–Vis study, different electronic transitions occurred in the hematite nanomaterials were identified, and the direct (1.90–1.97 eV) and indirect (1.21–1.46 eV) energy band gap values were estimated. Two photoluminescence peaks (one in visible and the other in near infrared region) detected in the spectra indicated the presence of various defect levels in the hematite nanoparticles within the energy band gap. Magnetic measurements exhibited the Morin transition to occur in these materials, while Mössbauer spectra successfully showed the magnetic contribution of the iron atoms occupying the core and the surface parts of the nanoparticles. Use of the extract in green synthesis produced hematite nanomaterials with extremely high dielectric constant (~ 10⁵) and significantly lower dielectric loss at low frequency and at room temperature when compared to the pristine one which signify their huge application potential. The results obtained from the characterization studies made on the pristine and green synthesized hematite nanomaterials revealed that the green synthesis of hematite nanoparticles using Tabernaemontana divaricata flower extract can efficiently modify their optical, magnetic and dielectric properties. Thus, using commercially cheap starting materials and extracts made from naturally available plant parts, materials having huge application potentials (like microwave and energy storage appliances) can be synthesized at low-cost by the simple green synthesis approach.