Defect dependent antioxidant activity of nanostructured nickel oxide synthesized through a novel chemical method

Nanostructured nickel oxide samples with different average crystallite sizes in the range 32–45 nm are synthesized through a novel chemical route using nickel chloride and ethanol amine as starting materials. The samples are characterized using XRD, TEM and XPS analysis. The antioxidant activity estimated by measuring the DPPH scavenging activity is found to increase with decrease in particle size. A study of the variation of antioxidant activity with particle size and comparison of the results with DC conductivity measurements lead to the conclusion that the antioxidant activity in NiO is defect dependent. The origin of antioxidant activity is traced to the presence of anion O2− vacancies in the nanostructured NiO samples as inferred from the study of variation of DC electrical conductivity of the samples in vacuum and air. The study leads to the possibility of tuning the antioxidant activity of transition metal oxides by changing the processing conditions.