Water-selective zeolite membranes: The yield of many gas-phase industrial reactions is limited by the formation of water as a by-product. Li et al. harnessed the water-sieving properties of NaA zeolite crystals by forming them into continuous defect-free membranes within tube reactors (see the Perspective by Carreon). These membranes can let water pass but reject gases such as hydrogen, carbon monoxide, and carbon dioxide (CO ₂ ). When these membranes were used in CO ₂ hydrogenation to form methanol with water as a by-product, substantial increases were observed in both the CO ₂ conversion and methanol yield. Science , this issue p. 667 ; see also p. 624

Among the current CO₂ capture technologies, membrane gas separation has many inherent advantages over other conventional techniques. However, fabricating gas separation membranes with both high CO₂ permeance and high CO₂/N₂ selectivity, especially under wet conditions, is a challenge. In this study, sub-20-nm thick, layered graphene oxide (GO)-based hollow fiber membranes with grafted, brush-like CO₂-philic agent alternating between GO layers are prepared by a facile coating process for highly efficient CO₂/N₂ separation under wet conditions. Piperazine, as an effective CO₂-philic agent, is introduced as a carrier-brush into the GO nanochannels with chemical bonding. The membrane exhibits excellent separation performance under simulated flue gas conditions with CO₂ permeance of 1,020 GPU and CO₂/N₂ selectivity as high as 680, demonstrating its potential for CO₂ capture from flue gas. We expect this GO-based membrane structure combined with the facile coating process to facilitate the development of ultrathin GO-based membranes for CO₂ capture.

We demonstrated for the first time that inkjet printing can be a low-cost, easy, fast, and scalable method for depositing ultrathin (7.5–60 nm) uniform graphene oxide (GO) nanofiltration membranes on polymeric supports for highly effective water purification. A large area (15 × 15 cm²) GO nanofiltration membrane was printed successfully on a modified polyacrylonitrile (M-PAN) support. Water permeance and rejection of small organic molecules (95%) of small organic molecules. Printed GO membranes also showed excellent performance in removing pharmaceutical contaminants, with ∼95% rejection and <10% water permeance decline over extended-period permeation testing. We believe that inkjet printing could be an effective method for preparing ultrathin GO membranes for effective water nanofiltration purification.

Crystalline materials with uniform molecular-sized pores are desirable for a broad range of applications, such as sensors, catalysis, and separations. However, it is challenging to tune the pore size of a single material continuously and to reversibly distinguish small molecules (below 4 angstroms). We synthesized a series of ionic covalent organic frameworks using a tetraphenoxyborate linkage that maintains meticulous synergy between structural rigidity and local flexibility to achieve continuous and reversible (100 thermal cycles) tunability of “dynamic pores” between 2.9 and 4.0 angstroms, with resolution below 0.2 angstroms. This results from temperature-regulated, gradual amplitude change of high-frequency linker oscillations. These thermoelastic apertures selectively block larger molecules over marginally smaller ones, demonstrating size-based molecular recognition and the potential for separating challenging gas mixtures such as oxygen/nitrogen and nitrogen/methane.

Membranes with molecular-sized, high-density nanopores, which are stable under industrially relevant conditions, are needed to decrease energy consumption for separations. Interfacial polymerization has demonstrated its potential for large-scale production of organic membranes, such as polyamide desalination membranes. We report an analogous ultrafast interfacial process to generate inorganic, nanoporous carbon-doped metal oxide (CDTO) nanofilms for precise molecular separation. For a given pore size, these nanofilms have 2 to 10 times higher pore density (assuming the same tortuosity) than reported and commercial organic solvent nanofiltration membranes, yielding ultra-high solvent permeance, even if they are thicker. Owing to exceptional mechanical, chemical, and thermal stabilities, CDTO nanofilms with designable, rigid nanopores exhibited long-term stable and efficient organic separation under harsh conditions.