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

Abstract

Magnetite and silica-coated magnetite (Fe 3 O 4 ) 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 Fe 3 O 4 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 Fe 3 O 4 and 16 ± 0.14 nm for silica-coated Fe 3 O 4 NPs. The SEM micrographs of the uncoated Fe 3 O 4 oxide revealed the agglomeration of the magnetite (Fe 3 O 4 ) particles. But the silica-coated Fe 3 O 4 oxide exhibited homogeneous distribution of particles with relatively less agglomerate of the particles. The particle size of Fe 3 O 4 NPs slightly increased with the temperature and precursor concentration. The antimicrobial activities of Fe 3 O 4 and silica-coated Fe 3 O 4 nanoparticles were tested against Gram-negative ( Escherichia coli and Pseudomonas aeruginosa ) and Gram-positive ( Staphylococcus aureus and Bacillus subtilis ) bacteria. Both Fe 3 O 4 and silica-coated Fe 3 O 4 NPs demonstrated better antimicrobial activities.