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1. Adsorption separation of heavier isotope gases in subnanometer carbon pores

   https://doi.org/10.1038/s41467-020-20744-6  

   Ujjain, Sanjeev Kumar; Bagusetty, Abhishek; Matsuda, Yuki; Tanaka, Hideki; Ahuja, Preety; de Tomas, Carla; Sakai, Motomu; Vallejos-Burgos, Fernando; Futamura, Ryusuke; Suarez-Martinez, Irene; et al (December 2021, Nature Communications)

   null (Ed.)

   Abstract Isotopes of heavier gases including carbon ( 13 C/ 14 C), nitrogen ( 13 N), and oxygen ( 18 O) are highly important because they can be substituted for naturally occurring atoms without significantly perturbing the biochemical properties of the radiolabelled parent molecules. These labelled molecules are employed in clinical radiopharmaceuticals, in studies of brain disease and as imaging probes for advanced medical imaging techniques such as positron-emission tomography (PET). Established distillation-based isotope gas separation methods have a separation factor ( S ) below 1.05 and incur very high operating costs due to high energy consumption and long processing times, highlighting the need for new separation technologies. Here, we show a rapid and highly selective adsorption-based separation of 18 O 2 from 16 O 2 with S above 60 using nanoporous adsorbents operating near the boiling point of methane (112 K), which is accessible through cryogenic liquefied-natural-gas technology. A collective-nuclear-quantum effect difference between the ordered 18 O 2 and 16 O 2 molecular assemblies confined in subnanometer pores can explain the observed equilibrium separation and is applicable to other isotopic gases. 

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2. High‐Performance Hemofiltration via Molecular Sieving and Ultra‐Low Friction in Carbon Nanotube Capillary Membranes

   https://doi.org/10.1002/adfm.202304672  

   Cheng, Peifu; Ferrell, Nicholas; Öberg, Carl M.; Buchsbaum, Steven F.; Jue, Melinda L.; Park, Sei Jin; Wang, Dan; Roy, Shuvo; Fornasiero, Francesco; Fissell, William H.; et al (August 2023, Advanced Functional Materials)

   Abstract Conventional dialyzer membranes typically comprise of unevenly distributed polydisperse, tortuous, rough pores, embedded in relatively thick ≈20–50 µm polymer layers wherein separation occurs via size exclusion as well as differences in diffusivity of the permeating species. However, transport in such polymeric pores is increasingly hindered as the molecule size approaches the pore dimension, resulting in significant retention of undesirable middle molecules (≥15–60 kDa) and uremic toxins. Enhanced removal of middle molecules is usually accompanied by high albumin loss (≈66 kDa) causing hypoalbuminemia. Here, the scalable bottom‐up fabrication of wafer‐scale carbon nanotube (CNT) membranes with highly aligned, low‐friction, straight‐channels/capillaries and narrow pore‐diameter distributions (≈0.5–4.5 nm) is demonstrated, to overcome persistent challenges in hemofiltration/hemodialysis. Using fluorescein isothiocyanate (FITC)‐Ficoll 70 and albumin in phosphate buffered saline (PBS) as well as in bovine blood plasma, it is shown that CNT membranes can allow for significantly higher hydraulic permeability (more than an order of magnitude when normalized to pore area) than commercial high‐flux hemofiltration/hemodialysis membranes (HF 400), as well as greatly enhance removal of middle molecules while maintaining comparable albumin retention. These findings are rationalized via an N‐pore transport model that highlights the critical role of molecular flexing and deformation during size‐selective transport within nanoscale confinements of the CNTs. The unique transport characteristics of CNTs coupled with size‐exclusion and wafer‐scale fabrication offer transformative advances for hemofiltration, and the obtained insight into molecular transport can aid advancements in several other bio‐systems/applications beyond hemofiltration/hemodialysis. 

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3. Polyamide nanofiltration membrane with highly uniform sub-nanometre pores for sub-1 Å precision separation

   https://doi.org/10.1038/s41467-020-15771-2  

   Liang, Yuanzhe; Zhu, Yuzhang; Liu, Cheng; Lee, Kueir-Rarn; Hung, Wei-Song; Wang, Zhenyi; Li, Youyong; Elimelech, Menachem; Jin, Jian; Lin, Shihong (April 2020, Nature Communications)

   Abstract Separating molecules or ions with sub-Angstrom scale precision is important but technically challenging. Achieving such a precise separation using membranes requires Angstrom scale pores with a high level of pore size uniformity. Herein, we demonstrate that precise solute-solute separation can be achieved using polyamide membranes formed via surfactant-assembly regulated interfacial polymerization (SARIP). The dynamic, self-assembled network of surfactants facilitates faster and more homogeneous diffusion of amine monomers across the water/hexane interface during interfacial polymerization, thereby forming a polyamide active layer with more uniform sub-nanometre pores compared to those formed via conventional interfacial polymerization. The polyamide membrane formed by SARIP exhibits highly size-dependent sieving of solutes, yielding a step-wise transition from low rejection to near-perfect rejection over a solute size range smaller than half Angstrom. SARIP represents an approach for the scalable fabrication of ultra-selective membranes with uniform nanopores for precise separation of ions and small solutes. 

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4. Structures and Dynamics of Complex Guest Molecules in Confinement, Revealed by Solid-State NMR, Molecular Dynamics, and Calorimetry

   https://doi.org/10.3390/molecules29071669  

   Haro_Mares, Nadia B; Döller, Sonja C; Wissel, Till; Hoffmann, Markus; Vogel, Michael; Buntkowsky, Gerd (April 2024, Molecules)

   This review gives an overview of current trends in the investigation of confined molecules such as water, small and higher alcohols, carbonic acids, ethylene glycol, and non-ionic surfactants, such as polyethylene glycol or Triton-X, as guest molecules in neat and functionalized mesoporous silica materials employing solid-state NMR spectroscopy, supported by calorimetry and molecular dynamics simulations. The combination of steric interactions, hydrogen bonds, and hydrophobic and hydrophilic interactions results in a fascinating phase behavior in the confinement. Combining solid-state NMR and relaxometry, DNP hyperpolarization, molecular dynamics simulations, and general physicochemical techniques, it is possible to monitor these confined molecules and gain deep insights into this phase behavior and the underlying molecular arrangements. In many cases, the competition between hydrogen bonding and electrostatic interactions between polar and non-polar moieties of the guests and the host leads to the formation of ordered structures, despite the cramped surroundings inside the pores. 

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5. Molecular driving forces for water adsorption in MOF-808: A comparative analysis with UiO-66

   https://doi.org/10.1063/5.0189569  

   Frank, Hilliary O; Paesani, Francesco (March 2024, The Journal of Chemical Physics)

   Metal–organic frameworks (MOFs), with their unique porous structures and versatile functionality, have emerged as promising materials for the adsorption, separation, and storage of diverse molecular species. In this study, we investigate water adsorption in MOF-808, a prototypical MOF that shares the same secondary building unit (SBU) as UiO-66, and elucidate how differences in topology and connectivity between the two MOFs influence the adsorption mechanism. To this end, molecular dynamics simulations were performed to calculate several thermodynamic and dynamical properties of water in MOF-808 as a function of relative humidity (RH), from the initial adsorption step to full pore filling. At low RH, the μ3-OH groups of the SBUs form hydrogen bonds with the initial water molecules entering the pores, which triggers the filling of these pores before the μ3-OH groups in other pores become engaged in hydrogen bonding with water molecules. Our analyses indicate that the pores of MOF-808 become filled by water sequentially as the RH increases. A similar mechanism has been reported for water adsorption in UiO-66. Despite this similarity, our study highlights distinct thermodynamic properties and framework characteristics that influence the adsorption process differently in MOF-808 and UiO-66. 

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