Magnetic, microstructural and photoactivated antibacterial features of nanostructured Co–Zn ferrites of different chemical and phase compositions.

Ferrites have found extensive uses in electrical, chemical and mechanical engineering, but their potential as biomaterials remains largely unexplored. Here we report on the use of a flash method based on urea decomposition to synthesize four different compositions of cobalt and zinc ferrite, including monophasic CoFe 2 O 4 , ZnFe 2 O 4 and Co 0.5 Zn 0.5 Fe 2 O 4 , and CoFe 2 O 4 /ZnFe 2 O 4 nanocomposite. Zn-ferrite nanoparticles were approximately the same size as those of Co-ferrite, but were better dispersed, rougher, more crystalline and less pronouncedly faceted. The mixed, monophasic Co 0.5 Zn 0.5 Fe 2 O 4 composition was morphologically most similar to single-phase Co-ferrite. In the biphasic mixture of CoFe 2 O 4 and ZnFe 2 O 4 , smooth and polydisperse Co-ferrite grains were coated by finer, cuboid and monodisperse Zn-ferrite nanoparticles. The porosity and the roughness of this composition were the highest, and so was its coercivity owing to the shielding of the ferrimagnetic Co-ferrite grains by the paramagnetic Zn-ferrite nanoparticles. Expectedly, the highest saturation magnetization (66.3 emu/g) was detected in Co-ferrite and the lowest (2.8 emu/g) in Zn-ferrite. Co-ferrite also exhibited the highest magneto-crystalline anisotropy, remanence and hysteresis loop area, while the highest exchange bias and susceptibility were found in the mixed, Co 0.5 Zn 0.5 Fe 2 O 4 composition. All four ferrite compositions were biocompatible with human fibroblasts, but they demonstrated different antibacterial activities against Gram-negative E. coli and Gram-positive S. aureus, with the biphasic mixture of CoFe 2 O 4 and ZnFe 2 O 4 being more effective than Co 0.5 Zn 0.5 Fe 2 O 4 , CoFe 2 O 4 or ZnFe 2 O 4. Further, all the compositions were more active against both bacterial species under visible light than in the dark, indicating the photocatalytic formation of electron-hole pairs and reactive oxygen species that exert a damaging effect on the bacterial cells as the prime mechanism of action. • Monophasic CoFe 2 O 4 , ZnFe 2 O 4 and Co 0.5 Zn 0.5 Fe 2 O 4 , and CoFe 2 O 4 /ZnFe 2 O 4 nanocomposite were synthesized and characterized. • CoFe 2 O 4 /ZnFe 2 O 4 nanocomposite contained Co-ferrite grains coated by Zn-ferrite nanoparticles, leading to high coercivity. • Biphasic mixture of CoFe 2 O 4 and ZnFe 2 O 4 had the highest antibacterial activity. • Photocatalytic formation of electron-hole pairs and reactive oxygen species is the prime mechanism of antibacterial action. • High biocompatibility of the examined compositions might encourage their use for numerous biomedical applications. [ABSTRACT FROM AUTHOR]