The Role of Hydrozyl Radicals in Advanced Ozidation Processes
The hydroxyl radical (HO°) is one of the most powerful oxidizing agent capable to react unselectively and instantaneously with other surrounding molecules. Since the discovery by Haber and Weiss in 1934 of its implication in the Fenton’s reaction, considerable studies have been devoted to this reactive oxygenated species. Hydroxyl radicals are omnipresent in the environment (natural water, atmosphere…) including human biological systems where the HO° has an important role during the immunity metabolism. Concerning the environmental issue, the HO° radicals have been the subject of increasing interest, particularly in the wastewater treatment field. European regulatory demands have become more stringent consecutively to the identification of the toxic effects on the biological organisms of numerous xenobiotics when released in the environment. Hazardous and toxic organics compounds present in industrial wastewater effluents are pollutants that need to be transform into harmless materials. Advanced oxidation processes (AOPs) are adequate techniques permitting to oxidize a broad range of organics pollutants and to achieve their in situ mineralization. These processes are based on the generation of HO° from chemical and/or physical systems. The chemicals are oxidizing agents: H2O2/FeII (Fenton), H2O2/FeIII (Fenton like), H2O2/catalyst, O3 (ozonation), and H2O2/O3 (peroxone) which are often associated with an irradiation technique (VUV, UV, pulse radiolysis, ultrasound). The contact of the organic compounds with the HO° initiates a radical-chain reactions leading to the mineralization of the organic compounds. The rate constant of HO° with organics is comprises between 107-109 M-1.s-1 range indicating a reaction rate near the diffusion control. The HO° is highly reactive and non-selective and for this reason it reacts with all surrounding chemicals, organic pollutants and inhibitors as well. The direct identification of transient radicals in aqueous media is very difficult and requires sophisticated techniques like pulse methods or electron spin resonance (ESR) associated with the spin trapping technique. Alternatively, the indirect detection of the HO° may be applied by adding probes or scavengers and by analysing the resulting adducts. Although the complete reaction mechanisms involving the HO° are complexes and still in general a puzzled issue, the role of HO° is known: it is involved in addition on unsaturated bonds, H abstraction and electron transfers. The kinetic models describing the oxidation mechanisms of AOPs are in good agreement with the experimental results, but unfortunately only for specific molecules in well defined conditions. Then, efforts still needed to try to establish a general model and particularly to unify the kinetics between aliphatic hydrocarbons and aromatics compounds by taking into account the role of inorganic ions.
Stéphane BARBATI
Laboratoire de chimie & Environnement,Université de Provence,3,Place Victor Hugo-case 29,F-13331 Marseille cedex 3,France
国际会议
2009 International Symposium on Environmental Science and Technology(2009环境科学与技术国际会议)
上海
英文
2493
2009-06-02（万方平台首次上网日期，不代表论文的发表时间）