In this study, the Ni1-xCoxFe2O4 (x=0.0, 0.5, 1) nanocomposites as nanocarriers in drug delivery systems and electrode material in supercapacitors was studied. The nanocomposites were successfully synthesized by a simple and eco-friendly method using rosemary leaf extract and thermal treatment method for the first time. The structural and magnetic properties of the Ni1-xCoxFe2O4 nanocomposites were examined and compared using various techniques. The investigation into the cytotoxicity of ternary blended transition nanoferrite, employed as quercetin (Que) nanocarriers (NCs) in drug delivery systems, was conducted using the MTT assay. By cyclic voltammetry (CV) characterizations, we demonstrated also the excellent performance as electrode material for supercapacitors of the as-prepared mixed ternary-transition-metal ferrites. The results showed that by controlling the biocompatibility and electrochemical properties of Ni1- xCoxFe2O4 nanocomposites, their performance in various practical applications in the biomedical field, as well as in wastewater treatment and water desalination applications, can be improved
