Oxidation of several chlorophenolic derivatives by UV irradiation and hydroxyl radicals

Abstract

The oxidation of some chlorophenols: 4-chlorophenol, 2,4-dichlorophenol, 2,4,6-trichlorophenol, 2,3,4,6-tetrachlorophenol, tetrachlorocatechol (3,4,5,6-tetrachloro-2-hydroxy phenol) and 4-chloroguaiacol (4-chloro-2-methoxy phenol) has been studied via single photodecomposition produced by polychromatic UV irradiation, oxidation by hydroxyl radicals generated by Fenton's reagent (hydrogen peroxide plus ferrous ions), and degradation by hydroxyl radicals produced by combinations of UV irradiation plus hydrogen peroxide, and UV irradiation plus hydrogen peroxide and ferrous ions (photo-Fenton system). These organics have been selected as models of chlorophenolic derivative pollutants present in wastewaters and groundwaters. The degradation levels obtained in each process are reported. The quantum yields in the single photodecomposition reaction and the rate constants between the chlorophenols and the hydroxyl radicals in the reaction with Fenton's reagent are determined. Finally, the additional contributions to the photodecomposition promoted by the radical reaction in the combined UV/H 2 O 2 and photo-Fenton systems are also evaluated.

The activity and selectivity of catalytic peroxide oxidation of chlorophenols over Cu–Al hydrotalcite/clay composite

“…That is, the oxidation reactivity of CPs greatly decreased with increasing substitution of chorine on the aromatic ring. This was consistent with the results obtained by some previous researchers [17,29,30]. Furthermore, the position of chlorine atoms on the aromatic ring has different effects on the oxidation rates of CP isomers with the same chlorine content.…”

“…Benitez et al [17] showed that the degradation rate sequence of different CPs was 4-CP > 2,4-dichlorophenol (2,4-DCP) > 2,4,6-trichlorophenol (2,4,6-TCP) > 2,3,4,6-tetrachlorophenol (2,3,4, at constant values of initial CP, hydrogen peroxide and ferrous concentration, pH, and temperature. This means that the position and content of Cl substituent on the aromatic ring strongly affected the peroxide oxidation of CPs.…”

Triclosan breakdown by Fenton-like oxidation

“…The kinetic constants reported in the literature for Fenton oxidation of chlorophenols at 25°C are several orders of magnitude lower than that obtained in this work for triclosan: 5 Â 10 À4 min À1 for 2,4,6-TCP, 7 Â 10 À4 min À1 for 2,4-DCP and 7 Â 10 À3 min À1 for 4-CP [46]. These results are in good agreement with the reported by Zhang and Huang [34] who concluded that triclosan has comparable or higher reactivities than the related substituted phenols resulting from its oxidative transformation with manganese oxides (i.e.…”

Composition and color stability of anthocyanin-based extract from purple sweet potato

“…Afterwards, as a result of polymerization reactions between the byproducts themselves and between them and some other compositions in PSP extract, both UV and fluorescent exposure led to remarkable increase in absorbance. UV showed a more drastic effect in comparison, which may be attributed to its potential to induce the oxidation of phenolic hydroxyls in PSP anthocyanins (Benitez et al, 2001). At the end of storage, a little decrease in absorbance was observed in the case of fluorescent irradiation, which may result from the instability of some polymeric intermediates formed.…”