A facile approach for the synthesis of porous hematite and magnetite nanoparticles through sol-gel self-combustion

Porous magnetite (Fe₃O₄) and hematite (α-Fe₂O₃) nanoparticles were prepared via the sol-gel auto-combustion method. The gels were prepared by reacting ferric nitrates (as oxidants) with starch (as fuel) at an elevated temperature of 200 °C. Different ratios (Φ) of ferric nitrates to starch were used for the synthesis (Φ = fuel/oxidant). The synthesized iron oxides were characterized by Fourier transform infrared (FT-IR) spectroscopy, Raman spectroscopy, X-ray diffraction (XRD) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer–Emmet–Teller (BET) and vibrating sample magnetometer (VSM) analysis techniques. The crystal structure, morphology, and specific surface area of the iron oxide nanoparticles (Fe₃O₄ and α-Fe₂O₃) were found to be dependent on the starch content. The FT-IR, XRD and VSM analysis of the iron oxides for Φ = 0.3 and 0.7 confirmed the formation of the α-Fe₂O₃ core, whereas at Φ = 1, 1.7, and 2 showed that Fe₃O₄ cores were formed with the highest saturation magnetization of 60.36 emu/g at Φ = 1. The morphology of the Fe₃O₄ nanoparticles exhibited a quasi-spherical shape, while α-Fe₂O₃ nanoparticles appeared polygonal and formed clusters. The highest specific surface area was found to be 48 m² g^–1 for Φ = 1.7 owing to the rapid thermal decomposition process. Type II and type III isotherms indicated mesoporous structures.