Search results for "Photocatalysis."
showing 10 items of 584 documents
ZnO nanorods covered with a TiO2 layer: simple sol–gel preparation, and optical, photocatalytic and photoelectrochemical properties
2015
In this work, composite core–shell ZnO/TiO2 materials were fabricated by deposition of TiO2 layers via a sol–gel method onto ZnO nanorods hydrothermally grown on an ITO electrode. Two approaches to the sol–gel procedure resulted in strongly different morphologies and thicknesses of the deposited TiO2 layer, as shown in electron microscopy studies. The decrease of the optical band gap energies of the ZnO/TiO2 composites by about 0.2–0.3 eV with respect to the TiO2 nanoparticles and ZnO nanorods was determined from UV-Vis diffuse reflectance spectra. The photocatalytic activities of the systems were determined by investigation of the decolorization of Methylene Blue (MB) in aqueous solution, …
Oxidation of oxalate ion in aqueous suspensions of TiO2 by photocatalysis and ozonation
2005
Abstract Oxalate anion has been oxidized in aqueous alkaline solution by using ozonation and photocatalysis in the presence of TiO 2 . A batch annular reactor has been used for carrying out reactivity runs in the presence of air/ozone, air/ozone/near UV irradiation, air/ozone/TiO 2 , air/near UV-irradiated TiO 2 and air/ozone/near UV-irradiated TiO 2 . The Langmuir–Hinshelwood kinetic model adequately describes the photocatalytic results obtained at different reaction conditions and allows determining the values of the kinetic and equilibrium adsorption constants. The contemporary presence of photocatalysis and ozonation shows a significant improvement of the process performance as the oxid…
Photocatalytic green synthesis of piperonal in aqueous TiO2 suspension
2014
Abstract Piperonal (heliotropine or 3,4-methylenedioxybenzaldehyde) has been synthesized by oxidizing piperonyl alcohol in aqueous UV-irradiated TiO2 suspensions. This compound was identified by GC–MS chromatography, 1H NMR and melting point determination. The other products of the photoprocess were 1,3-bis(3,4-(methylenedioxy)benzyl) ether (found in traces) and CO2, derived from the parallel pathway of photo-mineralization. Commercial and home-prepared TiO2 samples have been tested and the best selectivity (ca. 35%) was obtained by using the home-prepared ones. The reported green process allows to obtain an added value product (piperonal), upon partial oxidation of a cheap reagent.
ZrO2SiO2 mixed oxides: surface aspects, photophysical properties and photoreactivity for 4-nitrophenol oxidation in aqueous phase
1996
Abstract Mixed oxides of ZrO2 and SiO2 were synthesized by a sol-gel technique by using zirconyl chloride and commercial silica gel as starting materials. The paper reports some surface features of the powders and the photoreactivity results obtained in the oxidation of 4-nitrophenol in aqueous suspensions of powdered photocatalyst. The optical characterization of the suspension was also performed by measuring the photon flows reflected and absorbed by the reacting system. The photoactivity exhibited by the ZrO2SiO2 samples is very scarce especially if compared with that shown by a TiO2 sample tested at equal experimental conditions. The low photoreactivity can be justified on the basis of…
Removal of drugs in aqueous systens by photoassisted degradation
2005
Aqueous solutions of tetracycline, lincomycin and ranitidine were irradiated with UV light in homogeneous and heterogeneous systems. Two commercial polycrystalline TiO2 powders (Degussa P25 and Merck) were used as photocatalysts. After 5A h, an appreciable photolytic degradation of tetracycline and ranitidine was observed while the degradation of lincomycin was noticeably lower. As far as the mineralization is concerned, a small decrease of the TOC values was measured in the case of tetracycline whereas negligible variations were found for lincomycin or ranitidine. The presence of the photocatalysts greatly enhanced the degradation rates of the drugs with respect to those observed during th…
Some working principles of heterogeneous photocatalysis by semiconductors
1993
The present paper outlines some of the principles which are the working base for the photocatalytic processes: we refer to those photocatalytic processes performed using irradiated semiconductors. The steps related to the photoproduction of electron-hole pairs and their separation are discussed. It is also shown how the step of pair separation induces the formation of various chemical species, some of which are useful for the oxidation reactions. It is also shown that in order to reach a detailed description of photocatalytic processes it is necessary to have the knowledge of both the electronic and the physicochemical features of the semiconductors. The paper finally reports a case study r…
Multi-doped Brookite-Prevalent TiO2 Photocatalyst with Enhanced Activity in the Visible Light
2018
© 2018 Springer Science+Business Media, LLC, part of Springer Nature Abstract: Enabling solar and/or visible light-driven photocatalysis is a crucial step to access innovative applications in environmental science and sustainable energy. Titanium dioxide is the most used photocatalyst because of its low cost and toxicity, however it is also limitedly active under visible light irradiation due to its wide band gap. Among its polymorphs, brookite holds promising optoelectronic properties for visible light photocatalysis, which have to the best of our knowledge been limitedly exploited. Here, a C,S,N-doped brookite-based TiO2has been prepared via a rapid one-pot sol–gel synthesis. Besides subs…
Effect of linker distribution in the photocatalytic activity of multivariate mesoporous crystals
2021
The use of Metal-Organic Frameworks as crystalline matrices for the synthesis of multiple component or multivariate solids by the combination of different linkers into a single material has emerged as a versatile route to tailor the properties of single-component phases or even access new functions. This approach is particularly relevant for Zr6-MOFs due to the synthetic flexibility of this inorganic node. However, the majority of materials are isolated as polycrystalline solids, which are not ideal to decipher the spatial arrangement of parent and exchanged linkers for the formation of homogeneous structures or heterogeneous domains across the solid. Here we use high-throughput methodologi…
Photocatalytic oxidation of gaseous toluene on polycrystalline TiO2: FT-IR investigation of surface reactivity of different types of catalysts
2000
Commercial TiO 2 Merck and TiO 2 Degussa P25 powders were employed as the catalysts for the photo-oxidation of toluene. By using TiO 2 Merck benzaldehyde was found in gas phase as the main product of the toluene partial oxidation. After an initial transient period, this catalyst exhibited a high stability in the presence of water vapour in the gaseous mixture, whereas the photoproduction of benzaldehyde sharply decreases after removal of H 2 O from the feed IR spectra of the used catalyst revealed that in the absence of water vapour benzaldehyde is molecularly held on the catalyst surface. This feature was confirmed by co-adsorbing benzaldehyde and water on the fresh catalyst. By contrast, …
VOC's abatement: Photocatalytic oxidation of toluene in vapour phase on anatase TiO2 catalyst
1997
Publisher Summary The photocatalytic oxidation of toluene in the presence of water was performed in the gas–solid regime at room temperature by using TiO2. It has been found that the presence of water was beneficial to achieve the almost complete photo-oxidation of toluene to CO2 and H2O, in fact, only very small amounts of benzaldehyde vapor that is the main product of toluene partial oxidation, were detected. Volatile organic compounds, VOC's, are an important class of air pollutants usually found in the atmosphere of all urban and industrial areas. Toluene is one of these compounds, and because of its noxious nature several strategies have been identified to reduce its presence in indoor…