2D transition metal dichalcogenide membranes for efficient oil-water separation

Surfactant-stabilized oil-in-water (O/W) emulsions are challenging to separate due to their low interfacial tension and high stability. This study presents a strategy for addressing this challenge by developing polyethersulfone (PES) membranes modified with polydopamine (PDA)-functionalized layered chalcogenides – specifically germanium sulfide (GeS) and titanium disulfide (TiS₂). While TiS₂ is a classical transition metal dichalcogenide (TMD), GeS shares a similar two-dimensional layered structure and interfacial behavior, and is discussed here in the same context for functional comparison. Structural analyses using TEM, SEM, and AFM confirmed that PDA functionalization enhanced the hydrophilicity, surface roughness, and chemical stability of both materials while preserving their 2D morphology. The modified membranes exhibited outstanding oil rejection – 99.9 % for GeS@PES and 99.1 % for TiS₂@PES – compared to 95 % for pristine PES. GeS@PES also achieved a high pure water flux of 7200 LMH/bar and a flux recovery ratio (FRR) of 94.8 % over 10 filtration cycles, indicating strong antifouling behavior. In contrast, TiS₂@PES and pristine PES showed lower FRRs of 46.9 % and 45.2 %, respectively. These improvements are attributed to the synergistic effects of PDA-induced hydrophilicity and the high surface area and tunable interfacial properties of the layered chalcogenides, offering a promising solution for efficient O/W emulsion separation in wastewater treatment and oil spill remediation.