Carbon Nanotubes-Mediated Reduction of Hematite by Shewanella oneidensis MR-1

Abstract:

The worldwide carbon nanotubes (CNTs) industry is rapidly expanding with production capacity exceeding several thousand tons per year. After the service lives, CNTs will be ultimately released into the environment with their concentrations in soils increasing by 0.4-147 ng/kg/year and the consequent environmental impacts have received more and more attentions. Effects of CNTs on the redox reactions of Fe have not been studied, although the CNT-bound quinone functional groups can potentially act as an electron shuttle. In this study, we investigated the impact of multi-walled carbon nanotubes (MWCNTs) on the reduction of hematite by metal-respiring bacterium Shewanella oneidensis MR-1. Our results showed that the presence of MWCNT with concentration ranging from 0.05 to 1 g/L inhibited the reduction of hematite (Fe₂O₃) by up to 35%, likely due to the toxicity effects of MWCNTs. However, the microbially-reduced MWCNTs (0.1 g/L) stimulated the reduction of Fe(III) by 3.6 times, indicating the potential role of MWCNTs as an electron shuttle. These results suggest MWCNTs play a dual role in regulating the microbial reduction of hematite through both toxicity effects and electron shuttle. We plan to further explore the mechanism for the impact of MWCNTs on the redox reactions of iron by studying the influences of carboxyl functionalized MWCNTs, analyzing the impact of MWCNTs on bacterial growth and characterizing the quinone functional groups in MWCNTs. Potential results will provide a novel perception for the impact of CNTs on the biogeochemical cycles of iron.The worldwide carbon nanotubes (CNTs) industry is rapidly expanding with production capacity exceeding several thousand tons per year. After the service lives, CNTs will be ultimately released into the environment with their concentrations in soils increasing by 0.4-147 ng/kg/year and the consequent environmental impacts have received more and more attentions. Effects of CNTs on the redox reactions of Fe have not been studied, although the CNT-bound quinone functional groups can potentially act as an electron shuttle. In this study, we investigated the impact of multi-walled carbon nanotubes (MWCNTs) on the reduction of hematite by metal-respiring bacterium Shewanella oneidensis MR-1. Our results showed that the presence of MWCNT with concentration ranging from 0.05 to 1 g/L inhibited the reduction of hematite (Fe₂O₃) by up to 35%, likely due to the toxicity effects of MWCNTs. However, the microbially-reduced MWCNTs (0.1 g/L) stimulated the reduction of Fe(III) by 3.6 times, indicating the potential role of MWCNTs as an electron shuttle. These results suggest MWCNTs play a dual role in regulating the microbial reduction of hematite through both toxicity effects and electron shuttle. We plan to further explore the mechanism for the impact of MWCNTs on the redox reactions of iron by studying the influences of carboxyl functionalized MWCNTs, analyzing the impact of MWCNTs on bacterial growth and characterizing the quinone functional groups in MWCNTs. Potential results will provide a novel perception for the impact of CNTs on the biogeochemical cycles of iron.