Two-Dimensional Nanosheets and Layered Hybrids of MoS2 and WS2 through Exfoliation of Ammoniated MS2 (M = Mo,W)

Ammoniated MS2 (M = Mo,W) have been synthesized by reacting LixMS2 with a saturated solution of ammonium chloride. While, largely neutral NH3 is present in the interlayer of ammoniated MoS2 equal amounts of NH3 and NH4+ ions are present in the tungsten analog. The ammoniated MS2 exfoliate readily in a variety of polar solvents with exfoliation being best in water. Ammoniated WS2 forms a more stable colloidal dispersion compared to the Mo analog because the ammonium ions do not deintercalate easily from the layers even on exfoliation. The dispersions are comprised of large nanosheets of MS2 with lateral dimensions in the order of micrometers. The layers-could be restacked from the colloidal dispersions by evaporating the solvent. While the colloidal dispersions of ammoniated MoS2 yield NH3-free MoS2 on restacking, the dispersions of ammoniated WS2 yield WS2 intercalated with NH4+ ions. Co-stacking of MoS2 and WS2 nanosheets from a mixture of both the colloidal dispersions results in MoS2-WS2 hybrids in which the MoS2 and WS2 nanosheets are randomly stacked. Photoluminescence measurements of MS2 nanosheets and MoS2-WS2 hybrids indicate phase stability and existence of direct bandgap.