Improved binary and ternary nanostructured photocatalysts for gas phase detoxification of toluene

Photocatalysis using nanocrystalline materials with enhanced catalytic properties under ultraviolet (UV) or visible light has the potential for becoming one of the leading processes for the abatement of environmental problems. This work is focused on the study of the synthesis, characterization, and photocatalytic application of nanocrystalline binary and ternary oxide catalysts. These nanostructured materials were synthesized by conventional sol-gel preparation methods, by inverse micelles, and by incipient wetness impregnation. The photocatalysts were characterized using XRD, FTIR, UV-Visible, and Raman spectroscopy, SEM, and TEM. The addition of silica to titania reduces anatase crystallite size, increases surface area, and modifies surface acidity. The photocatalytic results demonstrate that 7.5% sol-gel based catalysts are more active than the Degussa catalysts (P25 TiO2, and 8% SiO 2-TiO2) using UV or Visible light on a catalyst mass basis. The photocatalytic activity using UV light is four times higher than the photocatalytic activity using visible light.; The photocatalytic activity of the WO3-TiO2 binary oxide catalysts was higher than P25 TiO2 and Degussa 8% SiO 2-TiO2 under UV or visible light, and depended strongly on the tungsten content. The addition of WO3 into the anatase crystal structure of titania may potentially affect the photocatalytic activity by several factors such as: increasing the absorption capacity in the visible region, presence of surface W sites enhancing oxygen activation, changing the surface acidity, increasing the surface area, and improving the surface trapping of electron and holes before recombination.; The results for the photocatalytic oxidation of toluene demonstrate that the addition of a third metal oxide does not improve the photocatalytic activity significantly in comparison with the binary oxides. The addition of Fe 2O3 reduces the activity of the catalyst.; All the samples prepared by the sol-gel method have less rutile than P25 TiO2. The intensity of the peaks associated to the anatase crystal phase decreased with an increase in the Si or W content.; Loading the Degussa and sol-gel catalysts with 2.5% MoS2 improves the photocatalytic performance for the toluene oxidation. The MoS2 was synthesized using an inverse micelle method and loaded on to the catalysts by incipient wetness impregnation. Doping the Degussa catalysts with MoS 2 dobles the initial activity relative to the unloaded catalysts. The MoS2 impregnated Degussa catalysts enhance the applicability of the visible light for the photocatalytic oxidation of toluene. Loading the 12.4% WO3-TiO2 sol-gel sample with 2.5% MoS2 increases the activity for the toluene oxidation using UV or visible light for the photocatalytic process. When MoS2 is loaded on a sample of 31.9% WO3-TiO2 no significant improvement of the activity occurred. All the MoS2 impregnated catalysts deactivate slower than the unloaded catalysts.