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Microwave discharge electrodeless lamps (MDELs). VI. Performance evaluation of a novel microwave discharge granulated electrodeless lamp (MDGEL)—Photoassisted defluorination of perfluoroalkoxy acids in aqueous media

Paper ID Volume ID Publish Year Pages File Format Full-Text
27368 44018 2011 8 PDF Available
Title
Microwave discharge electrodeless lamps (MDELs). VI. Performance evaluation of a novel microwave discharge granulated electrodeless lamp (MDGEL)—Photoassisted defluorination of perfluoroalkoxy acids in aqueous media
Abstract

Novel microwave discharge granulated electrodeless lamps (MDGELs; 5 mm × 10 mm), fabricated using vacuum-UV (VUV) transparent quartz envelopes, have been examined for the treatment of model contaminated wastewaters. Evaluation of these MDGELs was performed through the self-ignition of the lamps at low microwave power levels and by the photoassisted decomposition and defluorination of trifluoroacetic acid (TFA), heptafluorobutyric acid (HFBA) and perfluorooctanoic acid (PFOA) in aqueous solutions in a flow-through microwave photoreactor (MW/Photo) containing 20 such MDGELs. A conventional single rod-shaped microwave discharge electrodeless lamp (MDEL) and a low-pressure electrode Hg lamp were also used to compare the performance of these novel MDGELs. The dominant performance of the MDGELs was established by the defluorination kinetics per surface area of the light source immersed in the solutions and by the applied electric power of the lamps. At pH 10, the kinetics correlated with the carbon chain length and with the number of C–F bonds in the three fluorinated acids. Microwave irradiation of the single rod-shaped MDEL device achieved a defluorination level of 51% (TFA), 67% (HFBA), and 37% (PFOA) for a 240-min VUV/UV irradiation of solutions at initial pHs = 4.7–5.2, whereas at pH = 10 defluorination of TFA and HFBA was 100% complete within 120–135 min of irradiation; defluorination of PFOA was ca. 80% complete after 200 min. With the 20 MDGEL system, 100% defluorination of TFA and HFBA was achieved after 105 min, whereas 100% defluorination of PFOA required ca. 400 min of irradiation. A decomposition/defluorination pathway is described for PFOA on the basis of intermediates identified by LC–MS techniques that involved initial VUV/UV irradiation (185 nm and 254 nm) of the PFOA contaminant followed by subsequent losses of CO2 and –CF2 units to complete defluorination and degradation.

► We report on novel microwave discharge granulated electrodeless lamps (MDGELs). ► They were fabricated using vacuum-UV transparent quartz envelopes. ► Their performance was examined and evaluated through self-ignition at low microwave power levels, and by the photoassisted defluorination of fluorinated acids. ► Quantitative defluorination of these acids to fluoride ions and carbon dioxide was achieved in relatively short time.

Keywords
Microwave discharge electrodeless lamps; MDELs; Microwaves; Perfluoroalkylated contaminants; Perfluorooctanoic acid; Heptafluorobutyric acid; Trifluoroacetic acid
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Microwave discharge electrodeless lamps (MDELs). VI. Performance evaluation of a novel microwave discharge granulated electrodeless lamp (MDGEL)—Photoassisted defluorination of perfluoroalkoxy acids in aqueous media
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Publisher
Database: Elsevier - ScienceDirect
Journal: Journal of Photochemistry and Photobiology A: Chemistry - Volume 222, Issue 1, 5 July 2011, Pages 97–104
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Bioengineering
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