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Phenols
Published in Brian D. Fath, Sven E. Jørgensen, Megan Cole, Managing Global Resources and Universal Processes, 2020
Leszek Wachowski, Robert Pietrzak
For example, the concentration of phenol dissolved in rainwater collected in Portland, United States, was 0.08–1.2 |µg/L, but the mean concentration was 0.26 µg/L.[67] In diluted water solutions, phenol undergoes conversion to dihydroxybenzenes, nitrophenols, nitrosophenols, and nitrochinone, probably according to the radical mechanism with nitrate(V) ions with the use of hydroxyl radicals and phenoxyl.[68,69] The compound of 2,4,6-trichlorophenol occurs in water of different types as a result of exposure to chlorine and its effect on organic precursors. The mean concentration of chlorophenols in posttreated water varies from 0.003 to 1 µg/dm3.[69–71] If chlorine is used as a water disinfectant, different chlorophenols are formed,[72] while if chlorine dioxide is used, a variety of p-benzoquinones are formed.[73]
Advanced Oxidation of Phenolic Pollutants in Wastewater
Published in Maulin P. Shah, Sweta Parimita Bera, Günay Yıldız Töre, Advanced Oxidation Processes for Wastewater Treatment, 2022
Oxidation of phenol starts with the hydroxylation of an aromatic ring by free hydroxyl radicals. Hydroxylation causes the formation of dihydroxybenzenes such as catechol, resorcinol and hydroquinone, depending on the position of the hydroxylation in the aromatic ring. Resorcinol and hydroquinone are the products of meta- and parahydroxylation respectively, while catechol is the primary orthohydroxylation product. This is followed by the aromatic ring opening of the hydroxylation products with the subsequent formation of organic acids. These organic acids, except acetic acid, are finally oxidized to CO2 and H2O [41].
Gallic acid influence on azo dyes oxidation by Fenton processes
Published in Environmental Technology, 2022
Carlos Henrique Borges Tabelini, Juan Pablo Pereira Lima, André Aguiar
It is worth mentioning that the addition of GA in Fenton processes is not something trivial, because its cost would make the treatment of effluents containing dyes impracticable. An alternative would be to evaluate the use of solutions containing such natural compound or other phenols, as suggested by Dong et al [19]. A previous study found that aqueous extracts of Pinus taeda wood containing phenols derived from lignin, besides dihydroxybenzenes, increased the discolouration of a thiazine dye by Fe3+/H2O2 and Cu2+/H2O2 [43]. In the study by Papoutsakis et al. [44], involving an actual effluent from cork processing, they found that a fraction of it increased degradation via Fenton processes of different organic pollutants (phenol, imidacloprid, methomyl) in synthetic solution. This increase was attributed by the authors to the phenols present in the cork effluent, being one of them the GA, which kept the iron ions in solution in pH values above 3, as well as regenerated Fe2+.
Effect of cysteine using Fenton processes on decolorizing different dyes: a kinetic study
Published in Environmental Technology, 2022
Márcio Daniel Nicodemos Ramos, Larissa Aquino Sousa, André Aguiar
One way to increase HO• generation using Fenton processes and in order to make it durable, regardless of the initial oxidation state of iron ions and the slow reduction of Fe3+ to Fe2+ by H2O2 (Equation (2)), is to add efficient Fe3+-reducing mediators [7,8]. Synthetic phenols such as dihydroxybenzenes have been the most widely tested mediators, especially catechol [9–13]. Phenols derived from lignin such as vanillin [14], fungal metabolite 3-hydroxyanthranilic acid [15] and polyphenol gallic acid [11,16–18] have been evaluated as natural mediators, which have promoted improvements in degrading different organic pollutants.