Poly(ionic liquid)-Armored MXene Membrane: Interlayer Engineering for Facilitated Water Transport

Two-dimensional (2D) MXene-based lamellar membranes bearing interlayers of tunable hydrophilicity are promising for high-performance water purification. The current challenge lies in how to engineer the pore wall's surface properties in the subnano-confinement environment while ensuring its high selectivity. Herein, poly(ionic liquid)s, equipped with readily exchangeable counter anions, succeeded as a hydrophilicity modifier in addressing this issue. Lamellar membranes bearing nanochannels of tailorable hydrophilicity are constructed via assembly of poly(ionic liquid)-armored MXene nanosheets. By shifting the interlayer galleries from being hydrophilic to more hydrophobic via simple anion exchange, the MXene membrane performs drastically better for both the permeance (by two-fold improvement) and rejection (≈99 %). This facile method opens up a new avenue for building 2D material-based membranes of enhancing molecular transport and sieving effect.

Porous Liquid Crystalline Networks with Hydrogel-Like Actuation and Reconfigurable Function

A porous liquid crystalline network (LCN), prepared using a template method, was found to exhibit peculiar actuation functions. The creation of porosity makes the initially hydrophobic LCN behave like a hydrogel, capable of absorbing a large volume of water (up to ten times the sample size of LCN). When the amount of absorbed water is relatively small (about 100% swelling ratio), the porous LCN displays anisotropic swelling in water and, in the same time, the retained uniaxial alignment of mesogens ensures thermally induced shape change associated with LC-isotropic phase transition. Combining the characteristic actuation mechanisms of LCN (order-disorder transition of mesogens) and hydrogel (water absorption), such porous LCN can be explored for versatile stimuli-triggered shape transformations. Moreover, the porosity enables loading/removal/reloading of functional fillers such as ionic liquid, photothermal dye and fluorophore, which imparts a same porous LCN actuator with reconfigurable functions such as ionic conductivity, light-driven locomotion, and emissive color.

Molecular Bridges Stabilize Graphene Oxide Membranes in Water

Recent innovations highlight the great potential of two-dimensional graphene oxide (GO) films in water-related applications. However, undesirable water-induced effects, such as the redispersion and peeling of stacked GO laminates, greatly limit their performance and impact their practical application. It remains a great challenge to stabilize GO membranes in water. A molecular bridge strategy is reported in which an interlaminar short-chain molecular bridge generates a robust GO laminate that resists the tendency to swell. Furthermore, an interfacial long-chain molecular bridge adheres the GO laminate to a porous substrate to increase the mechanical strength of the membrane. By rationally creating and tuning the molecular bridges, the stabilized GO membranes can exhibit outstanding durability in harsh operating conditions, such as cross-flow, high-pressure, and long-term filtration. This general and scalable stabilizing approach for GO membranes provides new opportunities for reliable two-dimensional laminar films used in aqueous environments.