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Visible-light promoted photoprocesses on aqueous gallic acid in the presence of riboflavin. Kinetics and mechanism

Paper ID Volume ID Publish Year Pages File Format Full-Text
27146 44005 2010 6 PDF Available
Title
Visible-light promoted photoprocesses on aqueous gallic acid in the presence of riboflavin. Kinetics and mechanism
Abstract

Within the frame of possible precursory photoreactions in the generation of humic substances, the visible-light promoted interaction between riboflavin (Rf), a native photosensitizer in aqueous systems, and gallic acid (GA), a polyphenol naturally formed after lignin degradation, was investigated. A systematic kinetic and mechanistic study was conducted under aerobic conditions in aqueous media, through visible-light continuous photolysis, polarographic detection of oxygen uptake, stationary and time resolved fluorescence spectroscopy, time resolved near-IR phosphorescence detection and laser flash photolysis techniques. GA is degraded relatively fast in pH 7 aqueous solutions, where singlet molecular oxygen (O2(1Δg)), superoxide radical anion (O2−) and hydrogen peroxide (H2O2) – all three species photogenerated from triplet excited Rf – participate in the photoprocess. The general conclusion is that in natural waters GA can undergo spontaneous phototodegradation under environmental conditions. Radical species generated in the presence of Rf can participate in condensation or polymerization reactions promoting the natural synthesis of humic products.

Keywords
Gallic acid; Hydrogen peroxide; Photodegradation; Riboflavin; Singlet molecular oxygen; Superoxide radical anion
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Visible-light promoted photoprocesses on aqueous gallic acid in the presence of riboflavin. Kinetics and mechanism
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Publisher
Database: Elsevier - ScienceDirect
Journal: Journal of Photochemistry and Photobiology A: Chemistry - Volume 209, Issues 2–3, 25 January 2010, Pages 89–94
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
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Price after discount Only $4.95
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