Crystalline Phase Regulates Microbial Methylation Potential of Mercury Bound to MoS2 Nanosheets: Implications for Safe Design of Mercury Removal Materials.

Abstract

Transition-metal dichalcogenides (TMDs) have shown great promise as selective and high-capacity sorbents for Hg(II) removal from water. Yet, their design should consider safe disposal of spent materials, particularly the subsequent formation of methylmercury (MeHg), a highly potent and bioaccumulative neurotoxin. Here, we show that microbial methylation of mercury bound to MoS₂ nanosheets (a representative TMD material) is significant under anoxic conditions commonly encountered in landfills. Notably, the methylation potential is highly dependent on the phase compositions of MoS₂. MeHg production was higher for 1T MoS₂, as mercury bound to this phase primarily exists as surface complexes that are available for ligand exchange. In comparison, mercury on 2H MoS₂ occurs largely in the form of precipitates, particularly monovalent mercury minerals (e.g., Hg₂MoO₄ and Hg₂SO₄) that are minimally bioavailable. Thus, even though 1T MoS₂ is more effective in Hg(II) removal from aqueous solution due to its higher adsorption affinity and reductive ability, it poses a higher risk of MeHg formation after landfill disposal. These findings highlight the critical role of nanoscale surfaces in enriching heavy metals and subsequently regulating their bioavailability and risks and shed light on the safe design of heavy metal sorbent materials through surface structural modulation.