This study describes the adsorption of free radical TEMPO onto Al2O3 nanoparticles in the solvents with different polarities including DMF, methanol, acetone, THF, petroleum ether and n-hexane at ambient temperature to evaluate the radical scavenging activity. The adsorption percentage of radical is calculated by measuring the maximum adsorption intensity of the ultraviolet (UV) absorption spectrum of TEMPO in the presence and the absence of Al2O3 nanoparticles. The morphology of Al2O3 nanoparticles before and after adsorption of TEMPO is studied using transmission electron microscopy (TEM), X-ray diffraction (XRD) and Fourier-transform infrared (FT-IR) spectroscopy. The adsorption energy and other thermochemical data for the adsorption of TEMPO over different active sites of Al2O3 are estimated via dispersion corrected density functional theory (DFT + Disp). The donor-acceptor interactions between Al2O3 and TEMPO are calculated using natural bond orbital (NBO) theory. It is found that Al2O3 nanoparticles have efficient radical scavenging activity (RSA) in the range of 50-72%. Approximately, a linear relationship between dielectric constant of solvent and the absorption percentage of TEMPO over Al2O3 nanoparticles is achieved. So that with decreasing the polarity of solvent, the adsorption of TEMPO onto Al2O3 nanoparticles is increased. The adsorption of TEMPO over Lewis acidic sites of Al2O3 is more favored than Brønsted acidic and basic sites. The comparison between experimental and calculated IR spectra of TEMPO/Al2O3 complexes provides the good evidence for the adsorption of TEMPO onto the surface of Al2O3 nanoparticles.
Keywords: Chemistry; aluminum; free radicals; nitroxide.