Comparative Studies of Microwave- and Sol-Gel-Assisted Combustion Methods of Fe3O4 Nanostructures: Structural, Morphological, Optical, Magnetic, and Catalytic Properties

Spinel iron oxide (Fe3O4) nanostructures were synthesized by a simple microwave-assisted combustion method (MACM) using glycine as the fuel. For the purpose of comparative study, it was also prepared by a simple sol-gel-assisted combustion method (SACM). The as-prepared samples were characterized by powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, high-resolution scanning electron microscopy (HR-SEM), energy dispersive X-ray spectroscopy (EDX), UV-Visible diffuse reflectance spectroscopy (DRS), photoluminescence (PL) spectroscopy, and vibrating sample magnetometry (VSM) techniques. XRD and EDX results confirmed that the as-prepared products were pure spinel Fe3O4 without any impurity. Average crystallite size is found to be 12.15 and 28.47 nm for MACM and SACM products, respectively. HR-SEM analysis shows that nanospheres (NSs) and nanoparticles (NPs) have like morphologies by MACM and SACM methods, respectively. Band-gap (E-g) energy of the sample NSs is 2.44 eV, whereas the sample NPs have 2.19 eV. Magnetic hysteresis (M-H) loops revealed that the as-prepared Fe3O4 samples have superparamagnetic behavior at room temperature with saturation magnetization (M-s) values in the range of 38.53 and 46.51 emu/g for the sample NSs and NPs, respectively. The oxidation of benzyl alcohol into benzaldehyde reached a maximum of 67.43 % for NSs, whereas for NPs, the conversion was only 59.67 % with 100 % selectivity.