Reductive dechlorination of activated carbon-adsorbed trichloroethylene by zero-valent iron: carbon as electron shuttle.

Sequestration of organic contaminants in carbonaceous materials can significantly affect contaminant fate and transport. We investigated the reductive dechlorination of granular-activated carbon (GAC)-adsorbed trichloroethylene (TCE) by nanoscale zero-valent iron (nZVI) to understand the effect of sequestration on abiotic reactivity of organic contaminants. Significant reduction of TCE sequestered in GAC micropores was observed, even though direct contact with nZVI was unlikely. Reduction of sequestered TCE by reactive Fe(II) species or molecular hydrogen was ruled out as the reaction mechanisms. We propose that GAC served as the conductor for the transfer of electrons or atomic hydrogen from nZVI to the micropores, wherein adsorbed TCE molecules were reduced. An important implication for environmental remediation is that carbonaceous adsorbents not only function as a superb sink for organic contaminants but also allow them to be slowly degraded while being trapped.