No abstract

The interfacial design is critical in preparing high-performance mixed matrix membranes (MMMs), especially for the separation of larger sized components from mixtures. Herein, a facile and novel strategy was employed to design covalently linked zeolitic imidazolate framework-8-polydimethylsiloxane (ZIF-8@PDMS) MMMs without interfacial defects by a one-step synthesis route for ethanol recovery from ethanol aqueous solution. In this strategy, 3-glycidyloxypropyltrimethoxysilane (GOPTS) worked as the covalent linker of PDMS and amine-functionalized ZIF-8 nanoparticles (AZIF-8) simultaneously. The chemical structures and morphologies of AZIF-8 and AZIF-8@PDMS MMMs were demonstrated by various characterization techniques. The results exhibited that AZIF-8 and the MMMs were successfully prepared and AZIF-8 as the filler displayed better dispersion in the PDMS matrix and compatibility with the PDMS matrix as compared to ZIF-8 or GOPTS-modified ZIF-8 (GZIF-8). Therefore, AZIF-8@PDMS MMMs showed more excellent separation performance than ZIF-8 or GZIF-8-filled MMMs. In particular, AZIF-8@PDMS MMM with 7 wt % AZIF-8 loading exhibited the highest separation factor of 17.7 and a comparable total flux of 585.6 g/m2 h at 40 °C with 5 wt % ethanol aqueous solution, which were improved by 176.6 and 34.5%, respectively, in comparison with the pristine PDMS membrane, breaking the “trade-off” effect between the flux and separation factor. This study might provide some new insights into the fabrication of high-performance MMMs for pervaporation recovery of various organic systems.

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.

Cross‐linked polydimethylsiloxane (PDMS) is simultaneously water‐repellent and highly permeable to water vapor. Unfilled and silica‐free cross‐linked PDMS films of variable thickness (8–160 µm) are prepared and their water vapor transmission rates and permeability values are determined. Vapor transmission rate increases as membrane thickness decreased from 160 to 15 µm, but does not increase further when the film thickness is decreased to 8 µm. Rate‐limiting sorption is implicated as the cause of this effect and substantiated by a surface modification to enhance adsorption rate. Water vapor does not macroscopically condense on films thin enough to operate in this kinetic regime, and vapor transmission rates as high as 60% of the transmission rates through air are measured. A mechanism for water permeation is offered based on those proposed for nanoscopically confined water in carbon nanotubes and aquaporins.

Thin-film composite membranes formed by conventional interfacial polymerization generally suffer from the depth heterogeneity of the polyamide layer, i.e., nonuniformly distributed free volume pores, leading to the inefficient permselectivity. Here, we demonstrate a facile and versatile approach to tune the nanoscale homogeneity of polyamide-based thin-film composite membranes via inorganic salt-mediated interfacial polymerization process. Molecular dynamics simulations and various characterization techniques elucidate in detail the underlying molecular mechanism by which the salt addition confines and regulates the diffusion of amine monomers to the water-oil interface and thus tunes the nanoscale homogeneity of the polyamide layer. The resulting thin-film composite membranes with thin, smooth, dense, and structurally homogeneous polyamide layers demonstrate a permeance increment of ~20–435% and/or solute rejection enhancement of ~10–170% as well as improved antifouling property for efficient reverse/forward osmosis and nanofiltration separations. This work sheds light on the tunability of the polyamide layer homogeneity via salt-regulated interfacial polymerization process.