MoS₂ Membranes for Organic Solvent Nanofiltration: Stability and Structural Control

This paper reveals the chemical, structural, and separation stability of stacked molybdenum disulfide (MoS₂) membranes and establishes a low-cost and facile approach to developing stable, selective membranes for efficient molecular separation in an organic solvent. MoS₂ nanoflakes that were dominant by monolayer MoS₂ sheets as prepared via direct chemical exfoliation (chem-MoS₂) were found to be chemically and structurally instable, with a sharp decrease in the level of solute rejection within a few days. Few-layer MoS₂ nanoflakes were then fabricated using a hydrothermal method (hydro-MoS₂). A "supportive" drying process involving glycerol pretreatment and drying in an oven was established to allow realignment of nanoflakes and adjustment of interflake spacing. We have shown that the hydro-MoS₂ membranes provide a mean interflake free spacing of ∼1 nm, which is ideal for the separation of a model solute (Rose Bengal, size of ∼1.45 nm) from the solvent isopropanol (size of 0.58 nm) with good long-term stability over a 7 day test.