Efficient remediation of mercury-contaminated groundwater using MoS₂ nanosheets in an in situ reactive zone

Mercury contamination in groundwater is a serious global environmental issue that poses threats to human and environmental health. While MoS₂ nanosheets have been proven promising in removing Hg from groundwater, an effective tool for in situ groundwater remediation is still needed. In this study, we investigated the transport and retention behavior of MoS₂ nanosheets in sand column, and employed the formed MoS₂in situ reactive zone (IRZ) for the remediation of Hg-contaminated groundwater. Breakthrough test revealed that high flow velocity and MoS₂ initial concentration promoted the transport of MoS₂ in sand column, while the addition of Ca ions increased the retention of MoS₂. In Hg removal experiments, the groundwater flow velocity did not influence the Hg removal capacity due to the fast reaction rate between MoS₂ and Hg. With an optimized MoS₂ loading, MoS₂IRZ effectively reduced the Hg effluent concentration down to <1 μg/L without apparent Hg remobilization. Additionally, flake-like MoS₂ employed in this study showed much better Hg removal performance than flower-like and bulk MoS₂, as well as other reported materials, with the Hg removal capacity a few to tens of times higher than those materials. These results suggest that MoS₂ nanosheets have the potential to be an efficient IRZ reactive material for in situ remediation of Hg in contaminated groundwater.