Scavenging performance and antioxidant activity of γ-alumina nanoparticles towards DPPH free radical: Spectroscopic and DFT-D studies

The radical scavenging performance and antioxidant activity of gamma-alumina nanoparticles towards 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical were investigated by spectroscopic and computational methods. The radical scavenging ability of gamma-alumina nanoparticles in the media with different polarity (i.e. i-propanol and n-hexane) was evaluated by measuring the DPPH absorbance in UV-Vis absorption spectra. The structure and morphology of gamma-alumina nanoparticles before and after adsorption of DPPH were studied using XRD, FT-IR and UV-Vis spectroscopic techniques. The adsorption of DPPH free radical on the clean and hydrated gamma-alumina (1 1 0) surface was examined by dispersion corrected density functional theory (DFT-D) and natural bond orbital (NBO) calculations. Also, time-dependent density functional theory (TD-DFT) was used to predict the absorption spectra. The adsorption was occurred through the interaction of radical nitrogen N center dot and NO2 groups of DPPH with the acidic and basic sites of gamma-alumina surface. The high potential for the adsorption of DPPH radical on gamma-alumina nanoparticles was investigated. Interaction of DPPH with Bronsted and Lewis acidic sites of gamma-alumina was more favored than Bronsted basic sites. The following order for the adsorption of DPPH over the different active sites of gamma-alumina was predicted: Bronsted base < Lewis acid < Bransted acid. These results are of great significance for the environmental application of gamma-alumina nanoparticles in order to remove free radicals. (C) 2018 Elsevier B.V. All rights reserved.