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

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 Al(3+) 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 Al(3+) while it was converted into surface adsorbed (•)OHads and O2(•-) radicals at the Lewis acid sites of Fe(3+). The combination of both Lewis acid sites of iron and aluminum onto Fe2O3/Al2O3@SBA-15 enhanced the formation of (•)OHads 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.