SUMMARY
- The invention is a method to fabricate membranes made from exfoliated molybdenum disulfide (MoS2) for improved separation performance and membrane stability. Reverse osmosis (RO) membranes are undergoing widespread adoption in desalination applications as global water supplies are becoming increasingly stressed, forcing consumers to turn to more challenged water sources—brackish- and seawaters, for example—to meet demand. RO membranes require significant energy inputs to remove the salt entrained in these source waters, however, rendering the technology economical unattractive in some applications.
- This technology reduces the input energy required to remove dissolved solids from source water, extending the attractiveness of RO membrane separations to applications or regions that may have been previously economically unviable.
- By increasing membrane water permeability to near thermodynamic entitlement limits while keeping the salt rejection constant, the energy requirements for filtration of seawater and brackish water decrease by approximately 15% and 50%, respectively. The membrane further exhibits increased selectivity, especially towards smaller components such as boron, which would obviate the need for the multi-pass RO systems that are necessary for wastewater treatment and desalination of water for irrigation.
- Membranes are fabricated using by stacking exfoliated two-dimensional samples with precise, uniform, and optimal interlayer spacing through a novel drying and rewetting method enabled by covalent surface functionalization. Membranes fabricated using this approach demonstrate high separation performance without having to store the material in a hydrated condition, which contrasts starkly to existing fabrication methods, requiring precise control over the degree of hydration of the membrane (which must be stored in water for the entirety of their lifetime, limiting commercial viability).
Schematic of the hydration dependent structure of MoS2 membranes. Initially the hydrated membrane is disordered with mesoporous scale voids between layers. When partially dried, the large voids close but parts of the membrane restack to the bulk, decreasing the overall porosity of the membrane. When completely dried, the membrane is impermeable.