Abstract
Mixtures and composites of Ag/Ag2O and TiO2 (P25) with varying mass ratios of Ag/Ag2O were prepared, employing two methods. Mechanical mixtures (TM) were obtained by the sonication of a suspension containing TiO2 and Ag/Ag2O. Composites (TC) were prepared by a precipitation method employing TiO2 and AgNO3. Powder X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) confirmed the presence of Ag(0) and Ag2O. The activity of the materials was determined employing methylene blue (MB) as the probe compound. Bleaching of MB was observed in the presence of all materials. The bleaching rate was found to increase with increasing amounts of TiO2 under UV/vis light. In contrast, the MB bleaching rate decreased with increasing TiO2 content upon visible light illumination. XRD and XPS data indicate that Ag2O acts as an electron acceptor in the light-induced reaction of MB and is transformed by reduction of Ag+, yielding Ag(0). As a second light-induced reaction, the evolution of molecular hydrogen from aqueous methanol was investigated. Significant H2 evolution rates were only determined in the presence of materials containing more than 50 mass% of TiO2. The experimental results suggest that Ag/Ag2O is not stable under the experimental conditions. Therefore, to address Ag/Ag2O as a (photo)catalytically active material does not seem appropriate.
Highlights
Environmental problems related to water and air contamination, due to increasing world population and the resulting tremendous growth of industry and fuel combustion, have become a major concern of advanced science
methylene blue (MB) was was bleached bleachedwith withsignificantly significantlyfaster fasterreaction reactionrates rates than the rate of photolysis when exposed to UV/vis and visible light
The MB bleaching rate calculated for the TiO2-rich two methods. Mechanical mixtures (TM) 14 mixture suggests not all photogenerated charge carriers were used in the desired MB bleaching reaction, but some were that not all photogenerated charge carriers were used in the desired MB bleaching reaction, but some lost by reactions between excited TiO2 and Ag/Ag2 O, resulting in the reduction of Ag+
Summary
Environmental problems related to water and air contamination, due to increasing world population and the resulting tremendous growth of industry and fuel combustion, have become a major concern of advanced science. TiO2 is reported as the most durable photocatalyst, responding to all the above-mentioned requirements apart from broad range response to incident solar light due to its wide bandgap energy, (3.2 eV for anatase, 3.0 eV for rutile) which accounts for no more than 5% of the entire solar spectrum [1] This lack of photocatalytic activity under visible light illumination allows the use of TiO2 as a UV blocker in sunscreens [5]. The as-prepared mixtures and composites showed improved visible light activity for methylene blue (MB) bleaching, compared to blank TiO2 , and high photocatalytic H2 production from a methanol-water mixture under artificial solar light illumination
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