On the Discoloration of Methylene Blue by Visible Light

The discoloration of methylene blue in aqueous solution was studied under illumination by a fluorescent lamp, LEDs of red, green, and blue light, and a UV-A black light bulb. Overall results showed that methylene blue was discolored with and without the presence of any photoactive semiconductor. Out...

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Bibliographic Details
Published in:Journal of fluorescence 2019-01, Vol.29 (1), p.15-25
Main Authors: Sáenz-Trevizo, A., Pizá-Ruiz, P., Chávez-Flores, D., Ogaz-Parada, J., Amézaga-Madrid, P., Vega-Ríos, A., Miki-Yoshida, M.
Format: Article
Language:English
Subjects:
Analytical Chemistry
Aqueous solutions
Biochemistry
Biological and Medical Physics
Biomedical and Life Sciences
Biomedicine
Biophysics
Biotechnology
Bleaching
Discoloration
Dyes
Fluorescence
Fluorescent lamps
High performance liquid chromatography
Leuco dyes
Light
Light emitting diodes
Light irradiation
Light sources
Luminaires
Methylene blue
Original Article
Substrates
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Summary:The discoloration of methylene blue in aqueous solution was studied under illumination by a fluorescent lamp, LEDs of red, green, and blue light, and a UV-A black light bulb. Overall results showed that methylene blue was discolored with and without the presence of any photoactive semiconductor. Outcomes depended on the combination substrate-light source employed. Photosensitization was assumed as the discoloration mechanism followed upon visible light irradiation. Fluorescence spectroscopy and high-performance liquid chromatography were used to investigate the possible intermediates formed in the irradiated solutions. The detailed nature of formed species was not stablished, but it was proved that the dye molecule photo-bleached and partially defragmented in several intermediates including leuco dyes, demethylated phenothiazine dyes, and probably humic substances. Since the fluorescence intermediates found were similar for most of the irradiated solutions, it was assumed that comparable reactive species were responsible for the discoloration of the molecule in solution. Results proved the misconception of discoloration experiments found in the literature when employing visible light near the absorption region of the dye.
ISSN:1053-0509
1573-4994
DOI:10.1007/s10895-018-2304-6