Use of TiO 2/Cr-MCM-41 molecular sieve irradiated with visible light for the degradation of thiophene in the gas phase

Abstract

Photocatalytic processes using TiO 2 and UV radiation to eliminate pollutants are not yet suitable for industrial facilities due to their high consumption of energy. Transition metals incorporated onto mesoporous MCM-41 molecular sieves impregnated with TiO 2 constitute an alternative that allows the use of solar light. In this study, Cr-substituted MCM-41 were synthesized (Si/Cr = 100, 50 and ∞) and impregnated with TiO 2 (10 and 20 wt.%). Raman results showed the formation of anatase. Electronic spectroscopy and EPR exposed the formation of trivalent chromium after impregnation with TiO 2, which is related to a Cr–TiO 2 interaction. The synthesized photocatalysts, as well as TiO 2 P25, were tested in the degradation of thiophene in gaseous phase. A test with UV lamp showed 100% of conversion for 20%TiO 2/Cr-MCM-41(100) and exceeded the activity of TiO 2 P25, probably due to the higher dispersion of TiO 2 on the surface of the molecular sieve. During tests using visible light and 20%TiO 2/Cr-MCM-41(50) higher conversions than those of 20%TiO 2/Cr-MCM-41(100) and TiO 2 P25 were observed. These results indicate that chromium concentration is a key factor influencing the photocatalytic activity under visible light.