Surface polydopamine coating to boost molecular permeation of MoS2 lamellar membranes

The rigid MoS2 nanosheets are promising building blocks for establishing straight and regular two-dimensional (2D) channels to pursue high molecule permeances. However, the overtight stacking configuration of MoS2 laminates causes barriers for quick mass transports. In order to solve this issue, we propose the surface modification strategy using polydopamine (PDA) coating on MoS2 nanosheets for lamellar membrane assembly. This approach has the prominent merit of retaining the channel continuity, compared with the conventional intercalation route. Benefitting from the high hydrophilicity of PDA, the 2D PDA@MoS2 (PM) channels stacked by PDA decorated MoS2 sheets are easily solvated and the PM laminates deliver wide channels with d-spacings of up to 1.24 nm under wet states. The permeances of the solvated PM membranes are three times higher than the original MoS2 membranes and are superior to the existing nanofiltration membranes with comparable rejections as well. More interestingly, the PM membrane exhibits pH responsiveness and can achieve thorough sieving for a ternary system by using a single membrane. This study has identified a feasible route to expand the interlayer channels of 2D MoS2 membranes for boosting permeances.