Aluminum‐Modified Zinc Ferrichromite: A Mixed Metal Oxide Synthesis and Study of Enhanced Biological Properties

ABSTRACT Metal oxide nanoparticles have an extensive range of applications due to their remarkable photocatalytic, optical, electronic, and biological properties. In this work, nanocrystalline ZnFeCr 1‐x Al x O 4 (x = 0.00, 0.25, 0.5, 0.75, and 1.00) was successfully synthesized using the sol–gel method. Thermal stability and decomposition behavior were analyzed via TGA‐DTA, while UV–Visible spectroscopy confirmed the formation of the spinel structure and estimated an optical band gap of ∼1.65 eV for the equimolar composition. Structural and microstructural properties were studied using x‐ray diffraction, Fourier transform infrared spectroscopy, and field emission‐scanning electron microscopy, revealing single‐phase cubic spinel formation with tunable crystallite size and lattice strain. Zeta potential analysis showed a negative surface charge and colloidal stability. The nanoparticles demonstrated significant antibacterial activity against both Gram‐positive and Gram‐negative bacteria, especially Escherichia coli , with optimal performance at x = 0.50. The crystallite size spanned 14.35–17.60 nm with the concentration of Al 3+ , but the optical band gap was adjusted to a range of 1.65 eV with the equimolar mixture (x = 0.50). The nanoparticles of ZnFeCr 0.5 Al 0.5 O 4 had maximum antibacterial inhibition (20 mm against E. coli and 16 mm against Staphylococcus aureus at 10 mg mL −1 ) and proved to have a good biomedical perspective. The enhanced biological response is attributed to smaller crystallite size, surface defects, and improved charge distribution. These findings suggest that Al‐doped zinc ferrichromite nanoparticles are promising compounds for biomedical and antimicrobial applications.