Reductive Dehalogenation of Trichloroethylene with Zero-Valent Iron:  Surface Profiling Microscopy and Rate Enhancement Studies

Abstract

Mechanistic aspects of the reductive dehalogenation of trichloroethylene using zerovalent iron are studied with three different surface characterization techniques. These include scanning electron microscopy, surface profilometry, and atomic force microscopy. It was found that the pretreatment of an iron surface by chloride ions causes enhancement in the initial degradation rates. This enhancement was attributed to the increased roughness of the iron surface due to crevice corrosion obtained by pretreatment. The results indicate that the “fractional active site concentration” for the reactive sorption of trichloroethylene is related to the number of defects/abnormalities present on the surface of the iron. This was elucidated with the help of atomic force microscopy. Two possible mechanisms include (1) a direct hydrogenation in the presence of defects acting as catalyst and (2) an enhancement due to the two electrochemical cells operating in proximity to each other. The result of this study has potential for further research to achieve an increase in the reaction rates by surface modifications in a practical scenario.

Rapid and complete destruction of perchlorate in water and ion-exchange brine using stabilized zero-valent iron nanoparticles

“…, respectively, a 22% and 50% increase compared with that when Cl À was absent. On the other hand, Gotpagar et al (1999) reported that pretreatment of the iron surface by chloride ions was able to enhance the initial degradation rate of trichloroethylene with ZVI. Johnson et al (1998) observed that addition of chloride ions increased the rate of CCl 4 dechlorination with ZVI by as much as four times.…”

“…First, the addition of chloride ions can enforce the breakdown of the thin film of iron (hydr)oxides on ZVI surface. Hard Lewis base ions (such as Cl À , Br À , and I À ) were reported to be especially aggressive toward the passivating oxide layers to form strong complexes with iron centers (Gotpagar et al, 1999;Johnson et al, 1998). As the oxide layers are broken down by these diffusing anions, more ZVI surface becomes available for perchlorate reduction, resulting in improved perchlorate degradation.…”

“…As the oxide layers are broken down by these diffusing anions, more ZVI surface becomes available for perchlorate reduction, resulting in improved perchlorate degradation. Second, chloride can promote localized corrosion on iron with irregular pit shapes, and pitting on the iron surface provides added reactive sites for perchlorate reduction (Gotpagar et al, 1999;Prinz and Strehblow, 1998).…”

H<sub>2</sub> Gas Charging of Zero-Valent Iron and TCE Degradation

“…The first step in the reaction of Fe 0 and a TCE solution is TCE sorption onto the iron surface [11]. From the XRD analysis of the surface coatings, the iron surfaces are covered by iron oxides, Fe 3 O 4 (magnetite)/Fe 2 O 3 (maghemite).…”

Degradation of DCE and TCE by Fe–Ni nanoparticles immobilised polysulphone matrix

“…Later studies indicate that the introduction of a second, catalytic metal, results in increasing the half-life of Fe 0 [14][15][16][17]. Bimetallic combination of iron with metals such as nickel (Ni), copper (Cu), zinc (Zn), palladium (Pd) and silver (Ag) can degrade halogenated hydrocarbons in water much better than ZVI nanoparticles as electron transfer from Fe 0 is catalysed by the secondary metal and the rate of electron transfer is maintained constant [15,16,18,19].…”