Search results for "photocatalysi"
showing 10 items of 626 documents
Enhancing Selectivity In Photocatalytic Formation Of P-Anisaldehyde In Aqueous Suspension Under Solar Light Irradiation Via Tio2 N-Doping
2012
The photocatalytic partial oxidation of 4-methoxybenzyl alcohol to the corresponding aldehyde (p-anisaldehyde) was performed under simulated solar irradiation by using home prepared N-doped TiO2 catalysts. The photocatalysts were prepared by a sol–gel method, using TiCl4 as TiO2 precursor and NH4Cl, urea or NH4OH as N-doping sources. A commercial TiO2 (Degussa P25) was also used for comparison aims. The prepared catalysts were characterized by BET specific surface area, XRD, ESEM and UV-vis spectroscopy. The reactivity results show that (i) the doped catalysts are predominantly amorphous, and they show selectivity values far higher than those of the corresponding undoped ones and of well cr…
Influence of hydrogen peroxide on the kinetics of phenol photodegradation in aqueous titanium dioxide dispersion
1990
Abstract The influence of hydrogen peroxide on the phenol photodegradation rate under near UV radiation was investigated in homogeneous and heterogeneous systems: the heterogeneous systems were aqueous dispersions of titanium dioxide (anatase). The hydrogen peroxide photodecomposition reaction was also investigated for all the systems used. The highest rate of phenol photodegradation was observed in the heterogeneous system for the contemporary presence of hydrogen peroxide and oxygen. The rate equations for phenol photodegradation and hydrogen peroxide photodecomposition for both systems were obtained. A mechanistic model able to explain the main experimental results is also proposed.
Photocatalytic oxidation of acetonitrile in aqueous suspension of titanium dioxide irradiated by sunlight
2004
The photocatalytic oxidation of acetonitrile (CH3CN) was carried out in aqueous suspensions of polycrystalline TiO2 P25 Degussa irradiated by sunlight. A plug flow photoreactor in a total recycle loop was used for carrying out reactivity experiments in which the concentrations of acetonitrile, of its intermediate oxidation products and of not-purgeable organic carbon (NPOC) were monitored. The influence of the presence of strong oxidant species (H2O2, S2O82−, ClO−) on the process rate was studied. The dependence of acetonitrile photo-oxidation rate on the substrate concentration and on the catalyst amount was also investigated. The photodegradation rate of substrate and NPOC followed first …
ChemInform Abstract: Elemental Bromine Production by TiO2Photocatalysis and/or Ozonation.
2016
Significant production of elemental bromine (Br2 ) was observed for the first time when treating bromide containing solutions at acidic pH, with TiO2 photocatalyst, ozone, or a combination thereof. Br2 selectivities up to approximately 85 % were obtained and the corresponding bromine mass balance values satisfied. The process is general and may be applied at a laboratory scale for green bromination reactions, or industrially as a cheap, safe, and environmentally sustainable alternative to the currently applied bromine production methods.
Photocatalytic oxidation of cyanide in aqueous TiO2 suspensions irradiated by sunlight in mild and strong oxidant conditions
1999
Abstract The photocatalytic oxidation of free cyanide ions was carried out in aqueous aerated suspensions containing polycrystalline TiO2 (anatase) irradiated by sunlight. The influence of the presence of an organic compound (phenol) or of a strong oxidant (H2O2) on the photoprocess was also studied. The dependence of cyanide photo-oxidation rate on the following parameters: (1) cyanide concentration; (2) catalyst amount; and (3) phenol concentration was investigated. At the used experimental conditions, the kinetics of cyanide photo-oxidation is independent of the initial cyanide concentration and of the catalyst amount while it is affected by the phenol concentration and by the presence o…
TiO2-Based Photocatalysis for Organic Synthesis
2010
A major aim of the contemporary chemistry is to replace old environmentally hazardous processes with new, energy efficient routes allowing to reduce or totally avoid the use and production of harmful chemicals and to maximise the quantity of raw material that ends up in the final product. This chapter gives an account of TiO2-based selective photocatalysis as a green synthetic tool for the production of organics. Some case studies of the most common transformations carried out by means of photocatalytic reactions are illustrated in a midway perspective between photochemistry and organic chemistry.
Sunlight-induced reactions of some heterocyclic bases with ethers in the presence of TiO2
2005
The reactions between various heterocyclic bases and ethers induced by sunlight are reported. In several cases the photoreaction occurred with higher yields in liquid–solid heterogeneous system in the presence of polycrystalline TiO2 than in homogeneous system. The derivatives obtained with trioxane may give an easy entry to heterocyclic aldehydes.
An approach to polymer-supported triplet benzophenone photocatalysts. Application to sustainable photocatalysis of an α-diazocarbonyl compound
2013
Covalent immobilization of 4-hydroxybenzophenone on Merrifield resins affords new heterogeneous polymeric triplet photocatalysts. Their successful application in the intramolecular triplet-sensitized photolysis of a α-diazo β-keto ester has been achieved under sustainable criteria. Remarkably, the simple recovery and reuse for up to five sequential applications have been performed, although resulting in a slightly decreasing activity.
The Photocatalytic Activity of Novel, Substituted Porphyrin/TiO2-Based Composites
2010
Four novel porphyrins, 5-[3-(3-phenoxy)-propoxy]phenyl porphyrin, 5,15-di-[3-(3-phenoxy)-propoxy] phenyl porphyrin, 5,10,15-tri-[3-(3-phenoxy)-propoxy]phenyl porphyrin, 5,10,15,20-tetra-[3-(3-phenoxy)- propoxy]phenyl porphyrin, and their corresponding Cu(II) porphyrins, were synthesized and characterized spectroscopically. The photodegradation of 4-nitrophenol in aq. suspension was used to determine the photocatalytic activity of polycrystalline TiO2 samples which had been impregnated with the Cu(II) porphyrins, as sensitizers. The photocatalytic activity of the composite depends mainly on the amount of sensitizer on the TiO2 surface rather than the nature of the substituted porphyrins.
Selective C-H Activation of Methoxy Groups in a Three-Component Photoreaction.
2015
Surprisingly, the photocatalytic activation of ethers by H-abstraction and addition of the generated radicals to iminium ions formed in situ from aldehydes and anilines predominantly yielded the products of methoxy activation for dimethoxymethane and 1,2-dimethoxyethane. Various anilines and aromatic as well as aliphatic aldehydes are suitable reaction partners for this three-component photoreaction (Porta-type process) which also provides a simple access to 1,2-aminoalcohols.