Impact of Fe3+ and Al3+ co-doping on the structure, optical properties, and antibacterial activities of ZnO nanoparticles

Abstract

Understanding the potential role of nanoparticles (NPs) in the global antibiotic resistance threat is essential. This study focuses on the potential antibacterial applications of Zn1−2x(Fe, Al)xO (x = 0.0, 0.02, 0.035, 0.05, and 0.065) NPs synthesized using the citrate–nitrate solution combustion method. The synthesized NPs were characterized using XRD, FESEM, FTIR, UV–Vis, and PL spectroscopies. Their antibacterial performance was assessed using the standard disc diffusion method. The synthesized NPs exhibited a single-phase hexagonal wurtzite structure (P63mc space group), with crystallite sizes ranging from 8.5 to 19.74 nm, which decreased with increasing dopant concentration. Incorporation of Fe3+ and Al3+ significantly altered key parameters of ZnO NPs, including lattice constant, bond length, dislocation density, and microstrain. Furthermore, FESEM revealed the formation of relatively spherical grains with sizes ranging from 28.42 to 56.54 nm. FTIR confirmed the presence of metal–oxygen bonds, and changes in optical properties of ZnO NPs were observed in the UV and PL spectra due to the dopants. The direct optical band gap energies ranged from 3.29 eV to 3.43 eV, indicating a notable effect of doping. Incorporating Fe3+ and Al3+ into Zn1−2x(Fe, Al)xO led to a substantial enhancement in antibacterial efficacy against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), increasing the zones of inhibition (ZOI) (at a concentration of 33.33 mg/mL) from 14.14 mm to 16.14 mm and from 17.14 mm to 19.18 mm, respectively. Among all samples, Zn0.96Fe0.02Al0.02O NPs exhibited outstanding antibacterial activity, with ZOIs of 16.14 mm and 19.18 mm against S. aureus and E. coli, respectively. This study also suggests enhanced antibacterial mechanisms for the Zn0.96Fe0.02Al0.02O NPs.