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Photoassisted mineralization of aromatic and aliphatic N-heterocycles in aqueous titanium dioxide suspensions and the fate of the nitrogen heteroatoms

Paper ID Volume ID Publish Year Pages File Format Full-Text
48531 46511 2008 12 PDF Available
Title
Photoassisted mineralization of aromatic and aliphatic N-heterocycles in aqueous titanium dioxide suspensions and the fate of the nitrogen heteroatoms
Abstract

The photoassisted degradation of aromatic heterocycles (pyrrole, imidazole, pyrazole, isoxazole, oxazole and thiazole) and N-containing alicycles (aliphatic heterocycles: pyrrolidine, 4-butanelactam and 5-pentanelactam) was examined in liquid–solid dispersions. Complete mineralization (TOC) of the aromatic heterocycles was attained within ca. 1 h of UV irradiation of the TiO2/heterocycle system in acidic (pH 3), near-neutral (pH 6.0–7.6) and alkaline (pH 11) media. Mineralization kinetics were, in general, not appreciably influenced by the presence of acid but tended to be somewhat slower in alkaline media. N-alicycles were photomineralized more slowly than were the aromatics. The former could be mineralized in acidic and near-neutral media in less than 2 h, but not in alkaline media in which pyrrolidine, 4-butanelactam and 5-pentanelactam (and for comparison 4-butanelactone) were not mineralized even after 3 h of UV irradiation. Final products were, in all cases, CO2, NH4+ and NO3− ions and SO42− ions in the case of thiazole. Nitrogen (N2) gas was detected only during the photooxidation of pyrazole (contains two adjacent N heteroatoms) but not imidazole in which the N atom are separated by a C atom. The molar ratio NH4+/NO3− depended closely on the chemical structure of the substrates at the longer irradiation times. The site and mode of adsorption of these heterocycles onto the TiO2 particle surface were inferred from point charge calculations and the point of zero charge of the TiO2 (pHpzc ∼6.7); the position of elecrophilic attack by the photogenerated OH radicals was deduced from calculated frontier electron densities.

Keywords
Photomineralization; Titanium dioxide; Photodegradation; N-bearing compounds; Aliphatic heterocycles; Aromatic heterocycles; Alicycles
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Photoassisted mineralization of aromatic and aliphatic N-heterocycles in aqueous titanium dioxide suspensions and the fate of the nitrogen heteroatoms
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Publisher
Database: Elsevier - ScienceDirect
Journal: Applied Catalysis B: Environmental - Volume 78, Issues 1–2, 17 January 2008, Pages 139–150
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Catalysis
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
100% Money Back Guarantee
Full-text PDF Download
Online Support
Any Questions? feel free to contact us