Effect of citric acid on structural, optical, morphological properties of ZnO and the bactericidal applications against human pathogenic bacteria E. coli DH5α

Zinc oxide (ZnO) nano-particles (NPs) was synthesized by microwave-assisted solution combustion method using citric acid as fuel. The effect of citric acid concentration on the structural, optical and morphological properties was studied. The optimized concentration of citric acid for the synthesis of ZnO NPs was obtained. The high-resolution X-ray diffraction pattern confirming the crystalline nature of the hexagonal structured ZnO with P63mc (186) space group which is perfectly matching with the JCPDS card no. 01-089-1397. The crystallite size of the ZnO was estimated to be ∼22.57 nm. The scanning electron microscopy and high-resolution transmission electron microscopy images showed that the particles are quasi-spherical and homogenously distributed throughout the surface. The purity of the NPs was confirmed by EDX spectra which shows the presence of Zn and O elements. The presence of carboxyl groups and Zn-O bond stretching was confirmed by Fourier transform infrared spectroscopy. The optical energy bandgap of the ZnO NPs was decreases from 3.269 eV to 3.257 eV with decrease in citric acid concentration due to increase in the crystallinity of the material. The antibacterial effect of the ZnO NPs was performed at optimized concentration of ZnO. The ZnO shows the dose dependent inhibition on DH5α strain of Escherichia coli (E. coli) bacteria.