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Ind. Eng. Chem. Res. 2003, 42, 5024-5030
Destruction of Chlorinated Phenols by Dioxygen Activation under Aqueous Room Temperature and Pressure Conditions Christina Noradoun,‡ Mark D. Engelmann,‡ Matthew McLaughlin,‡ Ryan Hutcheson,‡ Kevin Breen,‡ Andrzej Paszczynski,† and I. Francis Cheng*,‡ Environmental Biotechnology Institute, University of Idaho, Moscow, Idaho, 83844-1052, and Department of Chemistry, University of Idaho, Moscow, Idaho 83844-2343
The complete destruction of separate mixtures of 1.1 mM 4-chlorophenol (aqueous) and 0.61 mM pentachlorophenol (aqueous slurry) take place in the presence of 0.5 g of iron particles in 10 mL of 0.32 mM ethylenediaminetetraacetic acid (EDTA) under ambient air under room temperature conditions. Under this reaction condition, the time required to reach complete disappearance to the detection limit of GC-FID for each compound was 4 h for 4-chlorophenol and 70 h for pentachlorophenol. Electrospray ionization mass spectral (ESI-MS) analysis of the 4-chlorophenol reaction mixture after its complete disappearance indicated non-chlorinated, primarily low molecular weight products; however, Cl- from 4-chlorophenol was not detected due to adsorption onto the iron or its corrosion products. Radical trap and control experiments suggest that the mechanism for destruction initiates with dioxygen activation, leading to the formation of reactive oxygen species (ROS) and ultimately ring opening of the phenolic compounds. This is the first example of an abiotic system capable of the complete destruction of an organic pollutant under room temperature and pressure conditions through dioxygen activation chemistry. Introduction The disposal of chlorinated and brominated industrial waste is a matter of increasing concern. In general, there are three acknowledged methods for the disposal of highly contaminated waste, incineration, biological oxidation, and chemical oxidation. Incineration above 1300 °C is necessary to avoid the formation of chlorinated dioxins and furans and is therefore costly.1-4 Alternative methods to the incineration processes for the complete degradation of halogenated organic pollutants under mild reaction conditions have been highly sought. Several oxidative and dechlorination methods have been considered, including chemical, photoelectrochemical and electrochemical, microbiological, supercritical, and wet air oxidations.5-24 All of these systems require expensive reagents, catalysts, or apparatuses and have reaction conditions harsher than room temperature and pressure (RTP). In the search for an ideal destruction process, it is important to keep in mind certain features: (i) the use of inexpensive reagents, (ii) reaction conditions as mild as possible, (iii) the minimal use of any catalysts, and (iv) any spent reagents and the products of such process should be as environmentally innocuous as possible. Given these restrictions we have sought to use the most abundant oxidative agent possible, dioxygen from air, in the demonstrated process. Many investigators have explored exhaustive oxidation of organic pollutants by the Fenton reaction
FeII + H2O2 f FeIII + HO- + HO•
(1)
* To whom correspondence should be addressed. Tel.: 208885-6387. Fax: 208-885-6173. E-mail:
[email protected]. † Environmental Biotechnology Institute. ‡ Department of Chemistry.
where the hydroxyl radical (HO•) is a potent oxidizing agent (E° > 1.8 V vs standard hydrogen electrode (SHE)) capable of reacting with most organics at diffusionlimited kinetics.25 Investigators have examined the possibility of using this reaction for the mineralization of organic pollutants, that is, oxidation to inorganic carbon compounds.20,26-31 However, in most cases the specific procedures require one or more of the following conditions; the use of acidic pH (
