Synthesis of Silica-Coated Fe(3)O(4) Nanoparticles by Microemulsion Method: Characterization and Evaluation of Antimicrobial Activity

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.