The present investigation reports on a simple technique for the preparation of single‐phase BiFeO3 powders using the polymerized complex method, starting from iron and bismuth nitrates. A mixed aqueous solution with citric acid, ethylene glycol, Bi, and Fe ions was polymerized. The formation mechanism, the homogeneity, and the structure of the obtained powders have been investigated by thermogravimetry, X‐ray diffraction (XRD), Raman spectroscopy, and scanning and transmission electron microscopy measurements. XRD results demonstrated that thermally induced crystallization of rhombohedral BiFeO3 from the Bi–Fe polymeric precursor occurred at temperatures as low as 400°C. Pure single‐phase BiFeO3 nanocrystallites without any impurity or amorphous phases were obtained when the precursor was treated at 600°C for 3 h.

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The cobalt ferrite (CoFe2O4) and silver-cobalt ferrite (Ag-CoFe2O4) nanoparticles were obtained through self-combustion and wet ferritization methods using aqueous extracts ofHibiscus rosa-sinensisflower and leaf. X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, and magnetic measurements were used for the characterization of the obtained oxide powders. The antimicrobial activity of the cobalt ferrite and silver-cobalt ferrite nanoparticles against Gram-positive and Gram-negative bacteria, as well as fungal strains, was investigated by qualitative and quantitative assays. The most active proved to be the Ag-CoFe2O4nanoparticles, particularly those obtained through self-combustion using hibiscus leaf extract, which exhibited very low minimal inhibitory concentration values (0.031–0.062 mg/mL) against all tested microbial strains, suggesting their potential for the development of novel antimicrobial agents.

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