This study explored a new green approach of the wet ferritization method to obtain magnetic cobalt ferrite (CoFe₂O₄) by using eucalyptus leaves aqueous extract as a reducing/chelating/capping agent. The spinel single cubic phases of prepared samples were proved by powder X-ray diffraction (XRD), Fourier-Transform Infrared (FTIR) and Raman spectroscopy. The average crystallite size is in the range between 3 and 20 nm. The presence of the functional groups coating the obtained material is confirmed from FTIR and thermal analysis. The scanning electron microscopy (SEM) analysis showed a morphology consisting of nanoparticle aggregates. Raman spectroscopy detects the characteristic bands of spinel-type CoFe₂O₄. Magnetic investigations reveal the formation of ferromagnetic compounds with cubic magnetic anisotropy and a blocking temperature around 140 K, specific for this type of material. The biosynthesized CoFe₂O₄ could be an attractive candidate for biomedical applications, exhibiting promising antimicrobial and antibiofilm activity, particularly against Gram-negative bacteria and fungal strains.

A series including single and mixed Ni-Co aluminates was obtained using the precursor method, with malic acid as a ligand. The malate precursors (polynuclear coordination compounds) were isolated and characterized by Fourier Transform Infrared (FTIR), Ultraviolet/Visible/Near Infrared (UV–Vis–NIR) spectroscopy, and thermal analysis. The UV–Vis–NIR spectra of the synthesized complex compounds highlighted the presence of Co²⁺ and Ni²⁺ in an octahedral environment. The thermal decomposition of these precursors led to Co_1−xNi_xAl₂O₄ (x = 0, 0.1, 0.25, 0.5, 0.75, 0.9, and 1) spinels. The effect of Ni²⁺ substitution on the structure, morphology, and optical properties of the obtained oxides was studied with the help of different characterization tools. XRD, FTIR, and Raman spectra evidenced the formation of the spinel phase. The size of the crystallites and the agglomeration degree of the particles decrease when the nickel content increases. The band gap (BG) value is not significantly influenced by the Ni substitution. The fluorescence spectra recorded for all samples show a similar pattern, but different intensities of the emission bands.

Nanosized CoFe_1.8RE_0.2O₄ (RE³⁺ = Tb³⁺, Er³⁺) ferrites were obtained through wet ferritization method. These ferrites were characterized by X-ray diffraction (XRD), scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM/HR-TEM), Fourier transform infrared spectroscopy (FTIR), Mössbauer spectroscopy and magnetic measurements. The XRD results revealed that the average crystallite size is 5.77 nm for CoFe_1.8Tb_0.2O₄ and 6.42 nm for CoFe_1.8Er_0.2O₄. Distribution of metal cations in the spinel structure estimated from X-ray diffraction data showed that the Tb³⁺ and Er³⁺ ions occupy the octahedral sites. TEM images indicated the presence of polyhedral particles with average size 5.91 nm for CoFe_1.8Tb_0.2O₄ and 6.80 nm for CoFe_1.8Er_0.2O₄. Room temperature Mössbauer spectra exhibit typical nanoscaled cobalt ferrite spectra in good agreement with XRD and TEM data. The saturation magnetization value (M_s) is 60 emu/g for CoFe_1.8Tb_0.2O₄ and 80 emu/g for CoFe_1.8Er_0.2O₄. CoFe_1.8RE_0.2O₄ nanoparticles showed similar antimicrobial efficacy against the five tested microbial strains, both in planktonic and biofilm state. The results highlight the promising potential of these types of nanoparticles for the development of novel anti-biofilm agents and materials.