Studies on antioxidant, optical, morphological and structural properties of co-doped zinc oxide nanoparticles

The study thoroughly investigated the optical, structural, and morphological properties, as well as the antioxidant activity, of cobalt doped zinc oxide nanoparticles (ZnO NP) using the formula Zn_(1-x)Co_xO (x = 0.00 ≤ x ≤ 0.03) synthesized via the biochemical co-precipitation approach. Rietveld refinement of XRD data revealed that the prepared nanoparticles have a single phase with the space group P6₃mc and a hexagonal wurtzite structure. Both XRD and FTIR analysis confirmed the structural changes in the lattice due to the replacement of cobalt ions for zinc ions. The morphology of the synthesized samples was examined using SEM and EDX analysis. The crystalline sizes and lattice parameters, determined through Rietveld refinement and Scherer formula, were found to be consistent, falling within the range of 20–40 nm. The estimated crystalline sizes for the nanoparticles were 21.7 nm, 33.3 nm, 36.2 nm, and 37.9 nm, for ZnO and Co-doped ZnO, respectively, as calculated using Rietveld refinement. UV–visible absorption measurements confirm the presence of exciton peak at 355 nm. The absorption spectra showed that the optical direct band gap, calculated using Tauc plots, decreases from 3.81 ± 0.04 to 3.71 ± 0.03 eV, as the Co content in ZnO NPs increases. The particle size distribution curve reveals that the sizes of the prepared samples range from 15 to 40 nm. Prepared nanoparticles show notable antioxidant properties. The radical scavenging activity percentage increases from 7.11 ± 0.60 to 28.45 ± 0.50% as the cobalt content in ZnO NP rises. PL spectra of all the prepared samples exhibit two prominent peaks at 399 nm and 538 nm.