Reductive dechlorination of hexachloroethane by sulfide in aqueous solutions mediated by graphene oxide and carbon nanotubes

The main objective of this study was to test the capability of CNMs to mediate the reductive dechlorination of chlorinated aliphatic hydrocarbons. We herein investigated the mediation effects of graphene oxide (GO) and multi-walled carbon nanotubes (CNT) on the reductive dechlorination of hexachloroethane by sodium sulfide in aqueous solutions (pH buffered). The presence of 10 mg/L CNT or GO enhanced the observed pseudo-first-order rate constant (k(obs)) of the reaction by a factor of 2 and 4, respectively; the enhancement effects were significantly greater than that of a soil humic acid (20 mg C/L). The strong enhancement effects of the test CNMs were attributable to the facilitated electron transfer by the graphitic surfaces and particularly to the activation of C-Cl bonds of hexachloroethane by the zigzag carbon atoms at the edges and defects of the carbon nanomaterials. Additionally, changes of pH and the presence of dissolved humic acid could significantly affect the CNT- and GO-mediated reactions. The reaction rate was markedly accelerated by the increase of pH, but was suppressed by the coexisting dissolved humic acid. The findings imply that CNMs have the potential to enhance reductive dechlorination of relatively recalcitrant contaminants, such as chlorinated aliphatic hydrocarbons, in natural aquatic environments. (C) 2014 Elsevier Ltd. All rights reserved.