Vibrational and structural study of environmentally persistent free radicals (EPFRs) formed by phenol dosed metal oxide nanoparticles

Environmentally persistent free radicals (EPFRs) are formed by the adsorption of substituted aromatic precursors on the surface of metal oxides and are known to have significant health and environmental impacts due to their unique stability. In this paper, the formation of EPFRs is studied by adsorption of phenol on ZnO, CuO, Fe2O3, and TiO2 nanoparticles (~10-50 nm) at high temperature. Electron paramagnetic resonance (EPR) indicates the formation of phenoxyl-type radical. Fourier transform infrared (FTIR) provides further evidence of EPFR formation by the disappearance of –OH groups, indicating the chemisorption of the organic precursor on the metal oxide surface. These results are further confirmed by inelastic neutron scattering (INS) which shows both ring out-of-plane bend and C-H in-plane bend motions characteristic of phenol adsorption on the studied systems. Also, the changes in the oxidation state of the metal cations are investigated by X-ray photoelectron spectroscopy (XPS) which shows that the...