Photoeffects on the Reduction of Carbon Tetrachloride by Zero-Valent Iron

Abstract

While reduction of chlorinated hydrocarbons by zero-valent iron in water is strongly influenced by the oxide layer at the metal−water interface, the role of the oxide in the dechlorination mechanism has not been fully characterized. In this paper, we investigate the semiconducting properties of the oxide layer on granular iron and show how the electronic properties of the oxide affect electron transfer to aqueous CCl4. Specifically, we determine whether conduction-band electrons contribute to the reduction of CCl4 by using light to increase the number of conduction-band electrons at the oxide surface and measuring how this treatment affects the rate and products of CCl4 degradation. We find that photogenerated conduction-band electrons do degrade CCl4 and, more importantly, shift the product distribution to more completely dechlorinated products that are indicative of two-electron transfer with a dichlorocarbene intermediate. Since the photogenerated electrons give different reduction products than the dark reducers, we conclude that the latter must not be conduction-band electrons. Further investigation of the reduction with photogenerated electrons is carried out by adding hole scavengers to the system. Isopropyl alcohol reacts with photogenerated holes to yield the α-hydroxyalkyl radical, which is known to reduce CCl4. With isopropyl alcohol present, we observe faster degradation of CCl4 with higher light intensity. Since no such increase is seen without isopropyl alcohol, the rate of CCl4 degradation by conduction-band electrons in water must not be limited by the number of photogenerated electron−hole pairs but rather by electron transfer from the oxide conduction band to CCl4.

Alkyl Bromides as Mechanistic Probes of Reductive Dehalogenation: Reactions of Vicinal Dibromide Stereoisomers with Zerovalent Metals

“…Zero-valent metals have been the focus of much recent attention in the environmental 27 community because they offer great promise in treating contaminated groundwater through their 28 ability to promote abiotic reductive dehalogenation (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12). Nevertheless, many basic questions 29 about the mechanism of these reactions remain unanswered.…”

Overcoming Barriers to the Remediation of Carbon Tetrachloride through Manipulation of Competing Reaction Mechanisms-Final Technical Report

“…• was confirmed by d8-isopropanol experiments, and radical trapping experiments using dimethylbutene (DMB) respectively (Danielsen and Hayes 2004;Elsner et al 2004 (Balko and Tratnyek 1998). However studies on goethite/Fe 2+ systems have shown that this does not occur (Elsner et al 2004), and we do not consider cleavage of 2 C-Cl bonds to be likely.…”

Role of pH in the Aqueous Phase Reactivity of Zerovalent Iron Nanoparticles with Acid Orange 7, a Model Molecule of Azo Dyes

“…With Fe_fresh-HCl after reaction, also peaks due to lepidocrocite ( -FeO(OH)) are observed ( Figure 1 [59,67].…”