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

• Hydroxylated Al2O3 showed high activity for photodegradation of phenolic compounds.
• α-Al2O3, boehmite and P-25 showed lower photocatalytic activity than Al2O3-400 ̊C.
• Rietveld analysis indicates presence of hydroxyl groups in Al2O3annealed at 400 ̊C.
• The generated hydroxyl groups are responsible for photocatalytic properties of Al2O.

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 TiO2, 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 Al2O3 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.

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