An in situ FT-IR study of photo-oxidation of alcohols over uranyl-anchored MCM-41: Possible reaction pathways

Photosensitive uranyl ions anchored onto MCM-41 mesoporous molecular sieves serve as remarkable photocatalysts in the degradation of alcohols, under ambient conditions of light, temperature, and air. The rates of conversion of alcohols to carbon dioxide was found to decrease in the order methanol > ethanol > 2-propanol > 1-propanol, with the difference in reactivity attributed to the stability of the carbon-centered radicals formed during photo-oxidation. Kinetics revealed that the photo-oxidation of alcohols followed a first-order reaction. A detailed in situ FT-IR analysis was used to identify the transient species formed during the photo-oxidation of ethanol and 2-propanof over uranyl-anchored photocatalyst. Acetic acid, ethyl acetate, and acetaldehyde were the intermediates obtained over UO22+/MCM-41 during photo-oxidation of ethanol, whereas acetate species, methyl acetate, and acetone were detected during photo-oxidation of 2-propanol. Based on the intenriediate species formed, their growth with respect to irradiation time, and their intensities, appropriate reaction mechanisms were proposed to corroborate our observations. (c) 2007 All fiahts reserved

Vapor-phase photocatalytic oxidation of volatile organic compounds over novel uranyl-anchored MCM-41 heterogeneous catalyst

In the present investigation, we exploited the visible region absorbance (lambda > 380 nm) of uranyl ions anchored onto mesoporous MCM-41 matrix for the vapor-phase photooxidation of volatile organic compounds (VOCs) such as benzene, toluene, cyclohexane, cyclohexene, and oxylene. In all cases, the only complete oxidation products, viz., carbon dioxide and water, were obtained. Further, the extent of conversion to carbon dioxide depended upon the nature of the organic compound. Under sunlight, the uranyl-anchored catalyst was found to be highly active for the degradation of a stable molecule like benzene, though longer irradiation times were needed for its complete conversion. This study signifies the potential applicability of the uranyl-anchored photocatalyst for applications related to air cleaning under ambient conditions of solar radiation and air

Uranyl-anchored MCM-41 as a highly efficient photocatalyst for the complete oxidation of methanol under sunlight

A photocatalyst that may exhibit high activity for oxidation of volatile organic compounds (VOCs) under solar radiation would offer a practical and economic means for the cleaning of air under environmental conditions. We report here for the first time that the uranyl ions anchored within the mesopores of MCM-41 may serve as an efficient heterogeneous photocatalyst for the complete destruction of methanol in vapor phase, and in the presence of sunlight and air. The uranyl-anchored MCM-41 was found to be more efficient than a TiO(2) photocatalyst in terms of CH(3)OH-->CO(2) conversion rates. The reversible and active participation of uranyl groups in the studied photocatalytic reaction was ascertained with the help of in situ fluorescence and electron paramagnetic resonance techniques, whereas the radiation-induced transient species over catalyst surface were monitored using in situ FTIR spectroscopy. The detailed reaction mechanism and the role played by uranyl ions in the photooxidation of methanol over UO(2)(2+)/MCM are elucidated on the basis of these results. (C) 200

A novel synthesis route for brookite rich titanium dioxide photocatalyst involving organic intermediate

© 2014, Springer Science+Business Media New York.High temperature stable brookite rich titanium dioxide of average crystallite size 20 nm has been prepared by a novel aqueous sol–gel method involving hydroxyethyl cellulose polymer (HEC) as an organic intermediate, wherein titania powder with brookite phase content as high as 44 wt% was obtained. The existence of brookite phase has been evident even after calcination of the samples at 900 °C, which also helped to maintain a specific surface area value of 5.5 m2g-1 compared to the surface area of 2.2 m2g-1 measured on pure titania sample with only rutile phase. The brookite rich titania exhibited superior photocatalytic activity under UV irradiation with a rate constant value of 0.011 min-1 compared to the value of 0.003 min-1 measured for pure rutile phase rich titania samples under similar conditions. The present study indicates that HEC assisted thermal decomposition can be an effective route to produce efficient photoactive brookite rich titania powders