Synthesis of Silica-Coated Fe₃O₄ Nanoparticles by Microemulsion Method: Characterization and Evaluation of Antimicrobial Activity

Magnetite and silica-coated magnetite (Fe₃O₄) nanoparticles (NPs) were synthesized by water-in-oil (W/O) microemulsion method from hydrated ferric nitrate, ferrous sulfate precursors and ammonia a precipitating agent with the assistance of Tween-80 and SDS surfactants. The synthesized materials were characterized by X-ray diffraction, scanning electron microscopy, thermal analyzer, and infrared spectroscopy. X-ray diffraction pattern of Fe₃O₄ showed that particles were phase pure with a cubic inverse spinel structure and FT-infrared spectra confirmed the presence of Fe-O bond in tetrahedral and octahedral interstitial sites. The crystallite size determined from powder XRD data with Scherer's equation was in the range of 7.3 ± 0.05 nm-10.83 ± 0.02 nm for uncoated Fe₃O₄ and 16 ± 0.14 nm for silica-coated Fe₃O₄ NPs. The SEM micrographs of the uncoated Fe₃O₄ oxide revealed the agglomeration of the magnetite (Fe₃O₄) particles. But the silica-coated Fe₃O₄ oxide exhibited homogeneous distribution of particles with relatively less agglomerate of the particles. The particle size of Fe₃O₄ NPs slightly increased with the temperature and precursor concentration. The antimicrobial activities of Fe₃O₄ and silica-coated Fe₃O₄ nanoparticles were tested against Gram-negative (Escherichia coli and Pseudomonas aeruginosa) and Gram-positive (Staphylococcus aureus and Bacillus subtilis) bacteria. Both Fe₃O₄ and silica-coated Fe₃O₄ NPs demonstrated better antimicrobial activities.