Green synthesis, characterization, and antibacterial activity of lime-juice-mediated copper–nickel mixed ferrite nanoparticles

This study reports the synthesis of nickel-substituted copper ferrite nanoparticles [Cu1−xNixFe2O4 (x = 0, 0.5, 1)] using lime juice as a reducing agent by sol–gel method. The structural, functional, surface morphological, optical, and magnetic properties of the samples were studied by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy with energy-dispersive spectroscopy (SEM–EDX), UV–visible, photoluminescence spectroscopy, and vibrating sample magnetometer, and their antibacterial activity was tested. The crystallite size sizes were found to increase from 32 to 37 nm with the substitution of nickel ions with copper ferrite. FTIR spectral analysis confirmed the formation of spinel ferrite. SEM images showed that ferrite nanoparticles had spherical shape. The band-gap results for pure synthesized ferrite nanoparticles were closer to the experimental values. The luminescence spectrum showed peaks corresponding to violet, green, and orange–red emissions. Magnetization measurements obtained at room temperature revealed a ferromagnetic behavior, and that the saturation magnetization and coercivity value increase with nickel substitution. All synthesized ferrite nanoparticles were studied for both Gram-positive (Staphylococcus aureus, Bacillus subtilis) and the Gram-negative (Klebsiella pneumoniae, Escherichia coli) bacteria for antibacterial properties. The Gram-negative bacterium E. coli showed high antibacterial activity with greater inhibition zone of Ni-substituted CuFe2O4 compared to pure CuFe2O4 and NiFe2O4 nanoparticles.