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Int. J. Environ. Res. Public Health 2019, 16(2), 198; https://doi.org/10.3390/ijerph16020198

Photocatalytic Mechanisms for Peroxymonosulfate Activation through the Removal of Methylene Blue: A Case Study

1
Department of Industrial Chemical & Environmental Engineering, Escuela Técnica Superior de Ingenieros Industriales, Universidad Politécnica de Madrid, Calle José Gutiérrez Abascal 2, 28006 Madrid, Spain
2
Department of Civil Engineering, Indian Institute of Technology Bombay, Powai, Mumbai-400076, India
*
Author to whom correspondence should be addressed.
Received: 5 December 2018 / Revised: 4 January 2019 / Accepted: 8 January 2019 / Published: 11 January 2019
(This article belongs to the Collection Municipal Wastewater Treatment and Sludge Treatment and Disposal)
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Abstract

Industrial activity is one of the most important sources of water pollution. Yearly, tons of non-biodegradable organic pollutants are discharged, at the least, to wastewater treatment plants. However, biological conventional treatments are unable to degrade them. This research assesses the efficiency of photocatalytic activation of peroxymonosulfate (PMS) by two different iron species (FeSO4 and Fe3+-citrate) and TiO2. These substances accelerate methylene blue removal by the generation of hydroxyl and sulfate radicals. The required pH and molar ratios PMS:Fe are crucial variables in treatment optimization. The kinetic removal is reduced by the appearance of scavenger reactions in acidic and basic conditions, as well as by the excess of PMS or iron. The best performance is achieved using an Fe3+-citrate as an iron catalyst, reaching the total removal of methylene blue after 15 min of reaction, with a molar ratio of 3.25:1 (1.62 mM of PMS and 0.5 mM Fe3+-citrate). Fe3+-citrate reached higher methylene blue removal than Fe2+ as a consequence of the photolysis of Fe3+-citrate. This photolysis generates H2O2 and a superoxide radical, which together with hydroxyl and sulfate radicals from PMS activation attack methylene blue, degrading it twice as fast as Fe2+ (0.092 min−1 with Fe2+ and 0.188 min−1 with Fe3+-citrate). On the other hand, a synergistic effect between PMS and titanium dioxide (TiO2) was observed (SPMS/TiO2/UV-A = 1.79). This synergistic effect is a consequence of PMS activation by reaction with the free electron on the surface of TiO2. No differences were observed by changing the molar ratio (1.04:1; 0.26:1 and 0.064:1 PMS:TiO2), reaching total removal of methylene blue after 80 min of reaction. View Full-Text
Keywords: sulfate radicals; peroxymonosulfate; iron activation; TiO2 activation; dye; synergistic effect sulfate radicals; peroxymonosulfate; iron activation; TiO2 activation; dye; synergistic effect
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Rodríguez-Chueca, J.; Alonso, E.; Singh, D.N. Photocatalytic Mechanisms for Peroxymonosulfate Activation through the Removal of Methylene Blue: A Case Study. Int. J. Environ. Res. Public Health 2019, 16, 198.

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