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Water and other small molecules frequently coordinate within metal‐organic frameworks (MOFs). These coordinated molecules may actively engage in mass transfer, moving together with the transport molecules, but this phenomenon has yet to be examined. In this study, we explore a unique water transfer mechanism in UTSA‐280, where an incoming water molecule can displace a coordinated molecule for mass transfer. We refer to this process as the "knock‐off" mechanism. Despite UTSA‐280 possessing one‐dimensional channels, the knock‐off transport enables water movement along the other two axes, effectively simulating a pseudo‐three‐dimensional mass transfer. Even with a relatively narrow pore width, the knock‐off mechanism enables a high water flux in the UTSA‐280 membrane. The knock‐off mechanism also renders UTSA‐280 superior water/ethanol diffusion selectivity for pervaporation. To validate this unique mechanism, we conducted 1H and 2H solid‐state NMR on UTSA‐280 after the adsorption of deuterated water. We also derived potential energy diagrams from the density functional theory to gain atomic‐level insight into the knock‐off and the direct‐hopping mechanisms. The simulation findings reveal that the energy barrier of the knock‐off mechanism is marginally lower than the direct‐hopping pathway, implying its potential role in enhancing water diffusion in UTSA‐280. [ABSTRACT FROM AUTHOR]

Structural flexibility is a critical issue that limits the application of metal-organic framework (MOF) membranes for gas separation. Herein we propose a mixed-linker approach to suppress the structural flexibility of the CAU-10-based (CAU = Christian-Albrechts-University) membranes. Specifically, pure CAU-10-PDC membranes display high separation performance but at the same time are highly unstable for the separation of CO2/CH4. A partial substitution (30 mol.%) of the linker PDC with BDC significantly improves its stability. Such an approach also allows for decreasing the aperture size of MOFs. The optimized CAU-10-PDC-H (70/30) membrane possesses a high separation performance for CO2/CH4 (separation factor of 74.2 and CO2 permeability of 1,111.1 Barrer under 2 bar of feed pressure at 35°C). A combination of in situ characterization with X-ray diffraction (XRD) and diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, as well as periodic density functional theory (DFT) calculations, unveils the origin of the mixed-linker approach to enhancing the structural stability of the mixed-linker CAU-10-based membranes during the gas permeation tests. Metal–organic frameworks have demonstrated great promise for gas separation membranes, but their structural flexibility hinders their stability and hence sieving performance. Here, the authors systematically tune the ratio of mixed linkers in CAU-10-based MOF membranes, finding the optimal ratio that suppresses structural flexibility and enhances CO2/CH4 separation performance. [ABSTRACT FROM AUTHOR]

Abstract: Single‐walled aluminosilicate nanotubes (AlSiNTs) are expected to possess mechanical strength comparable to that of single‐walled carbon nanotubes (SWCNTs). Most existing theoretical studies on the mechanical properties of AlSiNTs are based on defect‐free models, despite the fact that experimental results have revealed a variety of defects in AlSiNTs. Herein we developed a method for the modeling of defective AlSiNTs to enable the quantitative investigation of relationships among defect structures, structural stability, and mechanical properties of AlSiNTs. The defect structures dealt with in the proposed models are based on experimental findings. Our assessment of the stability and mechanical strength of nanotubes is based on multiscale computational tools, including density functional theory, molecular modeling, and nanoscale continuum modeling. Our study also identified the defect structure with the most pronounced impact on the stability and mechanical properties of AlSiNTs. [ABSTRACT FROM AUTHOR]

Gas permeation in metal-organic framework-based (MOF-based) membranes is often elucidated through the solution-diffusion model, where the adsorption and diffusion of gases play equally vital roles. This study draws attention to a unique phenomenon known as single-file diffusion (SFD) occurring within MOF membranes that possess ultramicropores with dimensions comparable to the gas molecules themselves. When SFD takes place, the separation performance becomes solely reliant on the adsorption quantities on the feed side of the membrane. As a proof of concept, we fabricated a UTSA-280 membrane and subjected it to testing using gas mixtures of CO 2 /N 2 and CO 2 /CH 4. Two crucial observations substantiate the occurrence of single-file diffusion. Firstly, in the gas mixtures, the diffusion coefficients of N 2 or CH 4 were observed to align closely with that of CO 2 , despite the intrinsic diffusion coefficients of CO 2 , N 2 , and CH 4 , as determined from single-gas permeation experiments, exhibiting differences. Secondly, the CO 2 mole fractions within the adsorption phase closely mirrored those in the gas phase on the permeate side. Given the high adsorption selectivity of UTSA-280 for CO 2 , the UTSA-280 membrane delivers outstanding permeation selectivity for CO 2 /N 2 (611) and CO 2 /CH 4 (80.7). Our experimental findings are supported by mesoscale kinetic Monte Carlo simulations, which confirmed the relation between the CO 2 compositions in the adsorption phase on the feed side and in the gas phase on the permeate side. Furthermore, density functional theory calculations revealed high energy barriers associated with CO 2 surpassing its counterparts, rendering such processes unfavorable, thereby reinforcing our experimental findings regarding single-file diffusion. [Display omitted] • The UTSA-280 membrane is fabricated through interfacial growth. • The UTSA-280 membrane exhibits high CO 2 /N 2 selectivity (611) • The UTSA-280 membrane exhibits high CO 2 /CH 4 selectivity (80.7). • Single-file diffusion within the UTSA-280 membrane is investigated. • Single-file diffusion could make permeation selectivity governed by adsorption. [ABSTRACT FROM AUTHOR]