(167h) Two-Dimensional Molybdenum Disulphide Membrane Separation: Stability, Structural Manipulation and Separation Performances | AIChE

(167h) Two-Dimensional Molybdenum Disulphide Membrane Separation: Stability, Structural Manipulation and Separation Performances

Authors 

Zhang, S. - Presenter, National University of Singapore
Jiang, S., National University of Singapore
Guo, B., National University of Singapore
Two-dimensional (2D) materials such as molybdenum disulfide (MoS2) present tremendous opportunities in membrane-based molecular separation. Compared to graphene oxide, MXene and other 2D inorganic materials, MoS2 show exceptional stability in organic solvents. A few studies have reported the preparation of MoS2 membranes for separation in aqueous solutions. However, there have been no investigations on the application of MoS2 membranes for organic solvent separation. In addition, multi-layer and mono-layer MoS2 nanosheets may be prepared by different approaches and have both been used for membrane preparation. Though studies have revealed that monolayer MoS2 structure is unstable in the ambient conditions, there have been no reports on the stability of MoS2 membranes.

This presentation covers our recent progress in 2D MoS2 membranes for organic solvent separation. In the first part, we prepared both multi-layer and mono-layer MoS2 nanosheets using different methods, and compared their structure, stability and performances after made into membranes. It’s found that multi-layer MoS2 membranes are looser in structure, and hence result in higher permeability to isopropanol and lower rejection to dyes. On the other hand, though mono-layer MoS2 membranes show better rejection to dyes in the short tests (within 3 hours), the rejection keeps decreasing over a 5-day tests, which is attributed to the limited stability of such nanosheets that lead to aggregation and breakage. To achieve high rejection and good stability, a ‘bridging’ agent is employed to regulate the interlayer spacing and nanosheet alignment of multi-layer MoS2 membranes, leading to improved rejection and stable performances over one week.

In the second part, mixed matrix membranes containing MoS2 nanosheets based on a 3-step layer-by-layer (LbL) method have been prepared, which provides a more cost-effective and scalable way to fabricate 2D membranes. Very interestingly, while the original LbL polyelectrolyte layer is impermeable to organic solvents, mixed matric membranes containing MoS2 nanosheets open the pathways to solvents while rejecting solutes whose molecular weight is around 300 Dalton. The phemonena is attributed to the lower of surface energy by MoS2 and its bridging effects. With a thin layer of < 50 nm, the mixed matrix membrane can achieve ethanol permeance –selectivity that surpasses the hypothetical upper bound, e.g., 92.9 % rejection for Victoria blue B (VBB, MW 506.08) with an ethanol flux of 11.4 L m-2 h-1 bar-1.