Few-layer molybdenum disulfide nanosheets functionalized with L-cysteine for selective capture of Cd2+ ions

Water purification and sensing using nanostructured thin films as filtration membranes is attractive due to their high surface area, which leads to the potential for high impurity retention rate, and superior sensitivity to dilute contaminants. Molybdenum disulfide (MoS2) is a widely investigated layered material that can be exfoliated and suspended in water at high concentrations. It can also be conveniently oxidized and functionalized without significantly affecting its electrical properties. All these characteristics indicate that MoS2 has the potential to be competitive with graphene in water purification and sensing applications. Here is presented a new protocol for the fabrication of MoS2 membranes functionalized with L-cysteine, an amino acid with the capability of coordinating to divalent metal ions including Cd and Hg in water. MoS2 nanosheets were exfoliated and functionalized with L-cysteine using a one-pot aqueous amide cross-linking process. These membranes preferentially absorb Cd2+ ions from water at concentration up to 76 +/- 15 mg Cd per gram of functionalized MoS2. The selectivity for Cd2+ makes L-cysteine functionalized MoS2 an excellent candidate material for selective heavy metal capture and detection.