Hydroxylated sol-gel Al₂O₃ as photocatalyst for the degradation of phenolic compounds in presence of UV light

Al₂O₃ was synthesized by the sol-gel method, dried at 100 C and annealed at 400, 500, 600 and 700 C, respectively. These materials were characterized and evaluated to be used as photocatalysts for the degradation of phenol in aqueous phase. Although Al₂O₃ is a well-known insulator, in the present study we show the feasibility of using Al₂O₃ synthesized by the sol-gel method as a catalyst for the photomineralization of hazardous organic molecules. The photocatalytic activity of these materials was higher than that of Degussa P-25 TiO ₂, and other commercial aluminas tested, particularly in the case of the sample of Al₂O₃ calcined at 400 C. The results of Nuclear Magnetic Resonance of solids (27AlMAS NMR) indicate that Al changes its coordination number during the calcination process. Rietveld refinement of the X-ray diffraction patterns denotes a notable hydroxylation in the Al ₂O₃ structure, which was not removed by thermal treatments. Complementary spectroscopic studies (UV-Vis and FTIR) as well as the characterization of the textural properties are reported. It is proposed that UV irradiation of the hydroxylated Al₂O₃ induces an effective separation of the electron-hole pairs and hence, promotes the photodegradation of phenolic compounds.