Qingshan Jason Niu

Aside from pore size distribution and surface charge, spatial charge plays a pivotal role in ion transport. Here, we report a mix-charged thin-film nanocomposite (m-TFN) membrane featuring a heterogeneous charge spatial distribution and uniform pore size for highly selective Li+/Mg2+ separation, engineered through incorporating imidazole-functionalized UiO-66-ID nanocrystals during the interfacial polymerization process. The addition of UiO-66-ID nanocrystals not only introduces additional positive charges into the polyamide network, creating heterogeneous spatial charge and reducing inner negative charges, but also modulates amine monomer diffusion and enrichment, promoting formation of a crumpled polyamide layer with a narrowed pore size distribution. The optimized m-TFN-0.06 membrane synergistically combines steric and Donnan effects, achieving exceptional Li+/Mg2+ selectivity (50-60) across simulated salt-lake brines with varying salinities (2000 ppm-5000 ppm) and Mg/Li ratios (10-50), and can even attain an unprecedented Li+/Mg2+ selectivity of 103.75 in ultrahigh-salt solutions (10500 ppm, Mg/Li=31.2). Solution-diffusion-electromigration analysis further demonstrates a better trade-off between Li purity and recovery, outperforming most commercial and reported benchmarks. This work establishes a new paradigm for mix-charged NF membrane design, integrating spatially engineered charge functionalities for advanced ionic separations.

Embedding inorganic nanoporous materials into thin-film nanocomposite membranes has emerged as a promising route to alleviate the inherent permeability–selectivity balance and durability constraints of polyamide reverse osmosis membranes.

Thin-film composite nanofiltration membranes face a trade-off phenomenon between ion selectivity and permeability due to the structural constraints of single monomers during interfacial polymerization (IP). Inspired by homogeneous precipitation, we decouple disorderly competitive reactions of comonomers through using in situ–generated H ⁺ during ultrafast IP processes as equilibrium-shifting inducers for the enamine reaction, thereby regulating the reaction sequence and relative amount of primary/secondary amine monomers. Combining the structural advantage of polyethyleneimine and piperazine monomers, the separation layer had a large free volume, high-density homogeneity, well-tuned nanopores, and tailored charge distribution. The staged-regulated membrane exhibited high water permeance and could even adapt to ion separation in ultrahigh-salt solutions (Mg/Li = 50, 20,000 parts per million), with a notable Mg ²⁺ /Li ⁺ selectivity improvement of more than 1600% over that of the control, directly mixed dual aqueous monomer-prepared membrane. This stage control strategy for precise nanofiltration membrane synthesis can provide extensive flexibility in modulating the IP process for application-specific membrane structure design.

Current research on emergent membrane materials with ordered and stable nanoporous structures often overlooks the vital facet of manufacturing scalability. We propose the preprocessed monomer interfacial polymerization (PMIP) strategy for the scalable fabrication of high-valent cluster-based metal-organic framework (MOF) membranes with robust structures. Using a roll-to-roll device on commercial polymer supports, Zr-fum-MOF membranes are continuously processed at room temperature through the PMIP approach. These large-area membranes demonstrate the preeminent hydrogen separation capabilities, boasting an order of magnitude of permeance and a thrice-enhanced selectivity when juxtaposed with conventional polymeric membranes. The obtained PMIP-Zr-fum-MOF membranes possess superior stability in water compared with interfacial polymerization (IP)-processed low-valent metal-ion-based ZIF-8 membranes. Moreover, we have implemented the PMIP strategy's universality to process the other four diverse MOF membranes. The proposal of PMIP significantly advances the scalable fabrication of water-stable high-valent cluster MOF membranes.

Interlayered thin-film composite (i-TFC) membranes based on 2D materials have been widely studied due to their high efficiency in mass transfer. However, the randomly stacked 2D nanosheets usually increase the fluid path length to some extent. Herein, in situ-grown quasi-vertically oriented 2D ZIF-L was introduced as an interlayer for preparing high-performance reverse osmosis (RO) membranes. Through the optimization of the crystal growth based on the inert polyethylene substrate, the novel i-TFC RO membrane via interfacial polymerization shows an outstanding water permeance (5.50 L m^-2 h^-1 bar^-1) and good NaCl rejection (96.3%). The membrane also shows promising potential in domestic water purification and organic solvent separation applications. Compared with the randomly stacked ZIF-L interlayer, the advantages of the vertically oriented one were ascribed to the excellent storage capacity of the amine monomers and the intensified gutter effect. This work will encourage more exploration on the interlayer architectures for high-performance i-TFC membranes.