Radiolytic oxidation and degradation of 2,4-dichlorophenol in aqueous solutions

Environ Sci Pollut Res Int. 2019 Jun;26(17):17055-17065. doi: 10.1007/s11356-019-04845-4. Epub 2019 Apr 17.

Abstract

Radiolytic oxidation of 2,4-dichlorophenol (2,4-DClP) in aqueous solutions demonstrated that ·OH predominantly adds to the unsubstituted positions of the aromatic ring and that elimination of chloride at the 4 position is important because the -OH group enhances the electron density at this position, which is favorable for the electrophilic reactions. The total yield obtained was 0.540 μmol/J. Radiation-induced degradation of 2,4-DClP was conducted in oxygen-free aqueous solutions (0.1, 0.25, 0.50, and 0.7 mmol/dm3), saturated with N2O, and aerated and under irradiation at low and high doses. The results demonstrate that the largest degradation occurred in oxygen-free solutions due to oxidation (·OH) and reduction reactions (H· and [Formula: see text]) and attack of the [Formula: see text] at the ipso position of -Cl, producing HCl. The degradation was affected to a large extent by the concentration and to a lesser extent by the presence or absence of oxygen in which the 2,4-DClP solution was irradiated. At concentrations less than 1 mmol/dm3, 2,4-DClP was degraded in the solution at an absorbed dose level of 1 kGy. At higher doses, the product concentrations increased to up to 30% of the dose required for the total degradation of 2,4-DClP; then, they decreased. A graph plotting the logarithm of the relative concentration as a function of the dose shows a linear correlation, which indicates that the radiolytic degradation followed pseudo-first-order reaction kinetics. The oxidation was followed by the chemical oxygen demand (COD). COD decreases when the solute concentration increases. This fact has a dependence on the presence or absence of oxygen too.

Keywords: 2,4-Dichlorophenol; Chemical oxygen demand; Hydroxyl radical; Radiation-induce degradation; Radiolytic oxidation; Radiolytical yield.

MeSH terms

  • Biological Oxygen Demand Analysis
  • Chlorophenols / analysis*
  • Chlorophenols / radiation effects
  • Gamma Rays*
  • Kinetics
  • Oxidation-Reduction
  • Solutions
  • Water Pollutants, Chemical / analysis*
  • Water Pollutants, Chemical / radiation effects
  • Water Purification / methods*

Substances

  • Chlorophenols
  • Solutions
  • Water Pollutants, Chemical
  • 2,4-dichlorophenol