Nanomaterials show strong potential for antibacterial treatments by targeting various bacterial strains and bypassing resistance through mechanical cell damage. This occurs when nanoparticles interact with bacterial cell walls, compromising their structural integrity. These mechanisms highlight nanomaterials as effective tools in combating infections. Using the sol–gel method, this study synthesized Co1-xAlxFe2O4 nanoferrites (x = 0.0, 0.2, 0.4, 0.6, 0.8). This study examines the effects of substituting trivalent Al3⁺ ions on cobalt ferrite nanoparticles’ structural and electrical properties and their antibacterial activity. X-ray diffraction confirmed the formation of Co1-xAlₓFe₂O₄ nanoferrites in the \(Fd\overline{3 }m\) space group, showing a shift towards lower 2θ angles in the (311) plane as Al3⁺ content increased. The crystal size reached 29.04 when (x = 0.0 and 0.4) and decreased to 25.29 when (x = 0.8). Fourier transform infrared spectroscopy identified absorption band characteristic of the cubic spinel structure, while field emission-scanning electron microscopy revealed polyhedral nanoparticles clustered in nanoscale formations. Particle sizes ranged from 37.21 nm at x = 0.4 to 31.11 nm at x = 0.8. A decrease in dielectric properties with increasing frequency was consistent with the Maxwell–Wagner model and Koops’ theory, while AC conductivity increased as charge carrier mobility rose with frequency. Antibacterial tests using the Agar well diffusion method showed that Escherichia coli was the most sensitive strain, followed by Klebsiella spp., with Streptococcus spp. Displaying the highest resistance. Nanoparticles at x = 0.8 demonstrated the most potent antibacterial activity. Overall, the results highlight that cation substitution within the cubic spinel lattice significantly impacts the structural, electrical, and antibacterial properties of cobalt ferrite nanoparticles.
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