Kinetic and mechanistic aspects of the oxidation of chlorophenols by ozone

Abstract

In Advanced oxidation processes (AOPs) radicals are considered to play an important role. Organic contaminations can in AOPs generally be converted to carbon dioxide, water, etc. The most important limitation to the application of AOPs, however, is their high costs, especially when complete mineralisation of the pollutants is pursued. The costs can be reduced by using the oxidant more efficiently, which can be achieved by introducing selectivity. Kinetic and mechanistic data are the basic requirements for optimization of the process. In this work, the influence of several different parameters (temperature, pH, UV irradiation and carbonate concentration) on the kinetics of the degradation ofortho -chlorophenol and para-chlorophenol by ozone was investigated. The pH is the most important parameter. Strongly related to the pH is the degree of ionisation of the phenol, which might be of importance since the shift from a slow to a fast reaction occurs at a higher pH in the case of para-chlorophenol as compared to the case with the more acidic ortho-chlorophenol. A strong indication for a radical mechanism is found in the decrease of the reaction rate in the presence of carbonate, a well known radical scavenger. A further indication is seen in the first step of the reaction, which is dechlorination of the aromatic compound.

The formation and influence of hydrogen peroxide during ozonation of para-chlorophenol

“…Most of the studies concerning the ozonation of CPs are focused on the degradation levels or the identification of some reaction by-products [5][6][7]. And in some cases, kinetic and mechanistic aspects of the ozonation of chlorophenols are proposed [1,8,9]. Hydrogen peroxide was detected during the ozonation of para-chlorophenol in our study.…”

Rapid photocatalytic destruction of pentachlorophenol in F–Si-comodified TiO2 suspensions under microwave irradiation

“…It can be seen that the Cl − amount increased obviously along with the degradation of PCP. It indicated that the chlorine atom was first removed, because the breaking of C-Cl bond is energetically more favorable than that of C-OH bond (the bond dissociated energy for a C-Cl bond is approximately 10 kcal/mol less than that for a C-OH bond) [33].…”

Assessment of degradation of eight commercial reactive azo dyes individually and in mixture in aqueous solution by ozonation

“…1. Boncz et al [20] indicated that pH value is the most important factor in the ozonation of chlorophenol, since pH determines the dissociation of organic compounds. Hsu et al [21] reported that increase in COD removal with increase in pH might be due to the self-decomposition of ozone to generate hydroxyl free radicals which can oxidize the organic compounds more efficiently.…”