Mechanism of Catalytic Ozonation in Fe₂O₃/Al₂O₃@SBA-15 Aqueous Suspension for Destruction of Ibuprofen

Abstract

Fe₂O₃ and/or Al₂O₃ were supported on mesoporous SBA-15 by wet impregnation and calcinations with AlCl₃ and FeCl₃ as the metal precursor and were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectra (FTIR) of adsorbed pyridine. Fe₂O₃/Al₂O₃@SBA-15 was found to be highly effective for the mineralization of ibuprofen aqueous solution with ozone. The characterization studies showed that Al–O–Si was formed by the substitution of Al³⁺ for the hydrogen of surface Si–OH groups, not only resulting in high dispersion of Al₂O₃ and Fe₂O₃ on SBA-15, but also inducing the greatest amount of surface Lewis acid sites. By studies of in situ attenuated total reflection FTIR (ATR-FTIR), in situ Raman, and electron spin resonance (ESR) spectra, the chemisorbed ozone was decomposed into surface atomic oxygen species at the Lewis acid sites of Al³⁺ while it was converted into surface adsorbed ^•OH_ads and O₂^•– radicals at the Lewis acid sites of Fe³⁺. The combination of both Lewis acid sites of iron and aluminum onto Fe₂O₃/Al₂O₃@SBA-15 enhanced the formation of ^•OH_ads and O₂^•– radicals, leading to highest reactivity. Mechanisms of catalytic ozonation were proposed for the tested catalysts on the basis of all the experimental information