Green synthesis of wurtzite ZnO nanoparticles via Indigofera tinctoria stem extract: linking crystallinity with photocatalytic and biological performance.

The green synthesis of ZnO nanoparticles has been reported through a simplified route using Indigofera tinctoria stem extract, utilised as a bio-reducing agent. ZnO with a hexagonal wurtzite structure and a 35.51 nm crystallite size was confirmed by diffraction peaks in the XRD pattern. The ZnO nanoparticles exhibit a hexagonal single phase (space group P63 mc), as determined by a Rietveld refinement study of XRD data. Symmetry between the obtained and observed diffraction patterns is shown by profile parameters (R p, R wp, and χ 2) with minimal values. The FTIR spectra showed a strong band at 458 cm-1 and a small band at 877 cm-1, attributed to Zn-O and Zn-OH distinctive stretching. SEM images revealed the formation of quasi-spherical ZnO nanoparticles exhibiting an average diameter of ∼36 nm. The TEM image also showed quasi-spherical to hexagonal particle shapes having an average particle size of 36.19 nm. The purity of ZnO nanoparticles was disclosed by the EDX spectrum, which showed the existence of Zn and O elements and the non-existence of peaks related to other elements. The ZnO nanoparticles showed absorption peak maxima at 374 nm with a calculated band gap of 3.21 eV, according to the UV-vis spectra. The zeta potential (ζ) distribution of ZnO nanoparticles was found to range from -54.8077 to +11.9954 mV at pH 7 in aqueous solutions with a hydrodynamic diameter of 129.480 nm. The Raman spectrum supported the presence of crystal defects in the synthesized ZnO. The remarkable MB dye degradation efficiency of ∼93% under sunlight irradiation at 120 minutes was revealed by the photocatalytic experiment's results. After the 5th cycle, the produced ZnO nanoparticles show ∼85% degradation efficiency. Potent antibacterial activities were demonstrated by the green-produced ZnO nanoparticles against both Gram-positive (+) and Gram-negative (-) microorganisms. Additionally, using the DPPH technique, the produced ZnO nanoparticles showed modest antioxidant properties.