Photocatalytic degradation of aromatic and alicyclic pollutants in water: by-products, pathways and mechanisms

1997 ◽  
Vol 35 (4) ◽  
pp. 73-78 ◽  
Author(s):  
Pierre Pichat
Keyword(s):  
Superoxide Dismutase ◽  
Active Species ◽  
Oh Radicals ◽  
Coupling Reactions ◽  
Fenton Process ◽  
Cation Radicals ◽  
Primary Products ◽  
Cl Atom ◽  
Fe Ions ◽  
By Products

Pyridine, 1-2-dimethoxybenzene, morpholine and lindane are mineralized by the TiO2-UV process. In the studies briefly reviewed here, their intermediate products, in particular the aliphatics, were identified both to determine what are the compounds that may be left in the treated water and to increase our understanding of the photocatalytic pathways. In addition to the oxidation and cleavage of the bonds, H(Cl) atom addition (or transfer) and coupling reactions were found to occur, which illustrates the complexity of photocatalytic degradations. Moreover, a comparison of the primary products of quinoline degraded either by photocatalysis or by the photo-Fenton process (Fe ions-H2O2-UV) showed that OH° radicals are not the only active species involved in photocatalytic degradations. From the effects of adding superoxide dismutase, it was inferred thatin situ formed O2−o anion-radicals intervene chemically, possibly by reacting with quinoline cation-radicals generated via electron transfer from quinoline to TiO2.

Die Reaktionen chlorierter Äthylene mit hydratisierten Elektronen und OH-Radikalen in wäßriger Lösung / The Reaction of Chlorinated Ethylenes with Hydrated Electrons and OH-Radicals in Aqueous Solution

1971 ◽  
Vol 26 (11) ◽  
pp. 1108-1116 ◽  
Author(s):  
R. Köster ◽  
K.-D. Asmus
Keyword(s):  
Rate Constant ◽  
Oh Radicals ◽  
Capture Process ◽  
Chlorinated Ethylenes ◽  
Diffusion Controlled ◽  
Hydrated Electrons ◽  
Cl Atoms ◽  
Type Radical ◽  
Cl Atom ◽  
Steric Hinderance

The reactions of chlorinated ethylenes with hydrated electrons and OH radicals have been investigated by using the method of pulse radiolysis. In addition γ-ray experiments were carried out. The reduction of the solutes occurs via a dissoziation electron capture process. The rate constant for the reaction of eaq⊖ with the more chlorinated compounds is essentially diffusion controlled (k= (1 - 2×1010 l-mole-1 sec-1). Vinylchloride and 1,2-trans-dichloroethylene react more slowly. This can be related to the higher stability of the C-Cl bond in these compounds.Hydroxyl radicals add to the C=C double bond of the chlorinated ethylenes. The rate constant for the reaction with vinylchloride was determined to 7.1 × 109 1 · mole-1 sec-1, and decreases with increasing degree of chlorination of the ethylenes. This effect is explained by the decreasing electron density on the C-atoms and steric hinderance. The hydroxyl radical always adds to the C-atom carrying the smallest number of Cl-atoms. In its reaction with 1,2-dichloro-, trichloro- and tetrachloroethylene a radical is produced with an OH group and a Cl-atom on the same C-atom. It eliminates HCl to form a C=O bond with k>7 × 105 sec-1. The type radical produced in this reaction has an optical absorption in the near UV (ε265 nm = (1-3)×103 1 · mole-1 cm-1).The OH radical addition products of vinylchloride and 1,1-dichloroethylene do not eliminate HCl and have no absorption in the visible and near UV.

scholarly journals Photocatalytic degradation of volatile chlorinated organic compounds with ozone addition

2017 ◽  
Vol 43 (1) ◽  
pp. 65-72 ◽  
Author(s):  
Hossein Ebrahimi ◽  
Farshid Ghorbani Shahna ◽  
Abdulrahman Bahrami ◽  
Babak Jaleh ◽  
Kamal ad-Din Abedi
Keyword(s):  
Removal Efficiency ◽  
Residence Time ◽  
Ozone Concentration ◽  
Photocatalytic Oxidation ◽  
Synergetic Effect ◽  
Expanded Graphite ◽  
Active Species ◽  
Oh Radicals ◽  
Chlorinated Organic Compounds ◽  
Combined System

Abstract The decomposition of hydrocarbons using combined advanced oxidation methods is largely considered owing to abundant production of OH radicals and the potential economic advantages. In this study, the synergetic effect of ozonation on photocatalytic oxidation of chloroform and chlorobenzene over expanded graphite-TiO2&ZnO Nano composite was investigated. The effect of introduced ozone concentration and residence time was also examined on removal efficiency. The results showed that the removal efficiency was significantly enhanced by the combined system resulting from the additional oxidation process causing active species to be increased. Increasing the introduced ozone concentration which generates more reactive compounds had a greater effect on the removal efficiency than that of residence time. However, from the mineralization point of view, the residence time had a dominant effect, and the selectivity towards CO2 was dramatically declined when the flow rate increased. Based on these results, the combined system is preferred due to higher removal efficiency and complete mineralization.

scholarly journals Tropospheric OH and Cl levels deduced from non-methane hydrocarbon measurements in a marine site

2007 ◽  
Vol 7 (17) ◽  
pp. 4661-4673 ◽  
Author(s):  
C. Arsene ◽  
A. Bougiatioti ◽  
M. Kanakidou ◽  
B. Bonsang ◽  
N. Mihalopoulos
Keyword(s):  
Eastern Mediterranean ◽  
Regional Scale ◽  
Oh Radicals ◽  
Atom Concentration ◽  
Diel Variations ◽  
Marine Site ◽  
Cl Atoms ◽  
Cl Atom ◽  
Good Agreement

Abstract. In situ continuous hourly measurements of C2–C8 non-methane hydrocarbons (NMHCS) have been performed from March to October 2006 at two coastal locations (natural and rural) on the island of Crete, in the Eastern Mediterranean. Well defined diel variations were observed for several short lived NMHCS (including ethene, propene, n-butane, n-pentane, n-hexane, 2-methyl-pentane). The daytime concentration of hydroxyl (OH) radicals estimated from these experimental data varied from 1.3×106 to ~4.0×106 radical cm−3, in good agreement with box-model simulations. In addition the relative variability of various hydrocarbon pairs (at least 7) was used to derive the tropospheric levels of Cl atoms. The Cl atom concentration has been estimated to range between 0.6×104 and 4.7×104 atom cm−3, in good agreement with gaseous hydrochloric acid (HCl) observations in the area. Such levels of Cl atoms can be of considerable importance for the oxidation capacity of the troposphere on a regional scale.

scholarly journals Tropospheric OH and Cl levels deduced from non-methane hydrocarbon measurements in a marine site

2007 ◽  
Vol 7 (3) ◽  
pp. 6329-6356 ◽  
Author(s):  
C. Arsene ◽  
A. Bougiatioti ◽  
M. Kanakidou ◽  
B. Bonsang ◽  
N. Mihalopoulos
Keyword(s):  
Eastern Mediterranean ◽  
Regional Scale ◽  
Diurnal Variations ◽  
Oh Radicals ◽  
Atom Concentration ◽  
Marine Site ◽  
Cl Atoms ◽  
Cl Atom ◽  
Good Agreement

Abstract. In situ continuous hourly measurements of C2-C8 non-methane hydrocarbons (NMHCS) have been performed from March to October 2006 at two coastal locations on the island of Crete, in the Eastern Mediterranean. Well defined diurnal variations were observed for several short lived NMHCS (including ethene, propene, n-butane, n-pentane, n-hexane, 2-methyl-pentane). The daytime concentration of hydroxyl (OH) radicals estimated from these experimental data varied from 1.3×106 to ~4.0×106 radical cm−3, in good agreement with box-model simulations. In addition the relative variability of various hydrocarbon pairs (at least 7) was used to derive the tropospheric levels of Cl atoms. The Cl atom concentration has been estimated to range between 0.6×104 and 4.7×104 atom cm−3, in good agreement with gaseous hydrochloric acid (HCl) observations in the area. Such levels of Cl atoms can be of considerable importance for the oxidation capacity of the troposphere on a regional scale.

Kinetic study and effect of water on methane oxidation to methanol over copper-exchanged mordenite

2020 ◽  
Vol 10 (2) ◽  
pp. 382-390 ◽  
Author(s):  
Vitaly L. Sushkevich ◽  
Jeroen A. van Bokhoven
Keyword(s):  
Carbon Monoxide ◽  
Water Molecule ◽  
Kinetic Study ◽  
Methane Oxidation ◽  
Active Species ◽  
Effect Of Water ◽  
Primary Products

Kinetic experiments show that both methoxy species and carbon monoxide are primary products. Adsorption of one water molecule reversibly blocks at least two copper atoms in active species.

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