A Redox-Active Molybdenum Disulfide Filter Capable of Meeting Stringent Hexavalent Chromium Drinking Water Guidelines

Recognition of the risks associated with exposure to low levels of hexavalent chromium (Cr[VI]) coupled with the high costs and complexity of conventional treatment methods necessitates the development of inexpensive, reliable technologies for removing Cr[VI] from drinking water sources. In response to this need, we created a filter medium consisting of molybdenum disulfide (MoS₂) nanoparticles attached to cotton wool. Under conditions relevant to drinking water, Cr[VI] was reduced to less toxic Cr[III] and sequestered on the filter medium. Under air-saturated solutions, competition by dissolved oxygen for reductive sites lowered the capacity of the medium for Cr[VI] removal and resulted in the release of appreciable amounts of molybdenum. Removing oxygen from water prior to treatment increased the capacity of the MoS₂-cotton by over an order of magnitude and decreased the mass of molybdenum released by over 80%. After Cr[VI] breakthrough, the activity of the MoS₂-cotton could be restored by storing the column for 24 h a dilute hydrochloric acid solution. The MoS₂-cotton filter media is attractive relative to existing Cr[VI]-removal technologies due to its low cost, lack of a need for pH adjustment and its ability to convert Cr[VI] into Cr[III]. In the absence of oxygen, the medium exhibits a treatment capacity that is similar or better than commercially available strong base anion exchange resins.