Yining Huang

Water scarcity remains a critical global challenge, driving the need for efficient technologies that can capture water directly from the atmosphere. Among various adsorbents, metal-organic frameworks (MOFs) have shown great promise for water capture owing to their tunable pore structures and chemical functionalities. In this work, a linker functionalization strategy incorporating embedded hydrophilic atoms was employed to design a new MOF, LMRC-2 (LMRC = Lanzhou Magnetic Resonance Center). LMRC-2 exhibits over a 10-fold increase in water uptake at low relative humidity (RH) compared to that of its hydrophobic parent MOF, while maintaining a comparable total capacity at high RH. Solid-state NMR spectroscopy provided direct evidence that the pyrrolic nitrogen atoms in the linker act as strong water adsorption sites. These results highlight the effectiveness of rational linker modification for tuning the hydrophilicity of MOFs and demonstrate that solid-state NMR can be a powerful probe for elucidating water adsorption mechanisms in porous materials.

The hydrogenation of carbon dioxide to formic acid has attracted considerable interest for carbon utilization and hydrogen storage. Metal–organic frameworks (MOFs), featuring open coordination sites and tunable pore structures, offer unique advantages for heterogeneous catalysis. Herein, we report the catalytic performance of a series of defect-engineered Ru-MOF catalysts for the hydrogenation of CO₂ to formate. The catalysts were synthesized by partially substituting the organic linker with 3,5-pyridinedicarboxylic acid (PYDC) to introduce controllable defect sites. Among the series, the defective Ru-MOF prepared with an optimal PYDC ratio of 30% used during synthesis (D3-Ru-MOF) exhibits enhanced catalytic performance for CO₂ hydrogenation to formate compared with its nondefective counterpart. After hydrogen pretreatment, D3-Ru-MOF achieves a turnover number (TON) of 1258 at 120 °C over 24 h while maintaining good structural stability. A clear structure–activity relationship was observed with catalytic performance dependent on defect density within the framework. This study demonstrates the effectiveness of defect-engineering in Ru-MOFs for improving CO₂ hydrogenation performance.

Understanding how mechanical stress reshapes flexible metal–organic frameworks (MOFs) is important for designing robust, stimuli-responsive CO ₂ sorbents.

This study investigates the molecular-level-induced-fit adsorption of acetylene (C₂H₂) and carbon dioxide (CO₂) in sql-SIFSIX-bpe-Zn, a flexible, anion-pillared ultramicroporous metal–organic framework (MOF). Sql-SIFSIX-bpe-Zn undergoes distinct pressure-dependent phase transitions, enabling a high selectivity for C₂H₂ over CO₂ and ethylene (C₂H₄). However, the unclear thermodynamic and kinetic mechanisms underlying this behavior, as well as limitations in models derived from single-crystal X-ray diffraction (SCXRD), necessitate further investigation. Using in situ multinuclear solid-state NMR (SSNMR) spectroscopy with isotopically enriched C₂D₂ and ¹³CO₂, we directly probed gas adsorption, framework dynamics, and competitive uptake in sql-SIFSIX-bpe-Zn across 153–298 K. Variable-temperature ²H SSNMR revealed a C₂D₂-induced pore opening between 253 and 233 K, marking a cooperative structural transformation process that maximizes acetylene adsorption. Complementary ¹³C and ¹⁹F SSNMR spectra show that both the SiF₆^2– pillars and bpe linkers participate in host–guest interactions through C–D···F hydrogen bonding and linker reorientation, while CO₂ remains bound near the linker region. In mixed-gas systems, CO₂ assists pore activation, but acetylene dominates adsorption, confirming its stronger affinity and selective uptake. These results provide a molecular-level mechanism for induced-fit adsorption and competitive selectivity in flexible hybrid ultramicroporous materials, guiding the design of next-generation adaptive MOF sorbents.

Defect engineering in metal-organic frameworks (MOFs) offers a promising approach to modify material properties by introducing controlled structural imperfections. Zr-based MOFs, particularly the well-known UiO-66, hold significant potential for diverse applications. Defects in UiO-66 can be generated using monocarboxylic acids as modulators, among other methods. However, resolving the atomic-level local structures of these defects remains a considerable challenge. In this study, the local structures of these defects are carefully characterized by multinuclear solid-state NMR spectroscopy (SSNMR) in combination with X-ray absorption fine structure (XAFS). In situ heating XAFS analyses at Zr K-edge reveal critical changes in the local structure of Zr during the removal of trifluoroacetic acid (TFA), including the decreased Zr-O coordination numbers and alterations in Zr-Zr bond distances. Multinuclear ¹H, ¹³C, ¹⁹F, ^35/37Cl, ¹⁷O solid-state NMR methods are used to identify capping species and defect-associated species. Subsequently, the engineered defects are found to significantly improve the catalytic performance of Pt nanoparticles (NPs) integrated into the defective UiO-66 framework. Pt-UiO-66 with defects exhibits much improved hydrogen evolution reaction (HER) activity and stability compared to the Pt-UiO-66 without defects.

Efficient separation and storage of radioactive noble gas isotopes [krypton-85 ( ⁸⁵ Kr) and xenon-131m/133/135 ( ^131m/133/135 Xe)] from off-gas during spent nuclear fuel reprocessing are vital for environmental protection and noble gas recovery. Metal-organic frameworks (MOFs) are promising adsorbents, yet atomic-level insights into Xe and Kr adsorption remain limited. Here, we report the first application of high-field solid-state ⁸³ Kr nuclear magnetic resonance (NMR), alongside extensive ¹²⁹ Xe NMR, to investigate gas adsorption in eight MOFs representing three design strategies: ultramicroporous one-dimensional–channel MOFs with pore sizes matching noble gas diameters, functionalized MOFs, and MOFs with open metal sites. Single-gas and coadsorption studies reveal distinct adsorption sites, guest-host interactions, and gas dynamics in each MOF. Most MOFs retain crystallinity after exposure to 60-kilogray γ radiation. Several radiation-sensitive MOFs exhibit enhanced stability in the presence of Xe, suggesting that Xe adsorption enhances framework stability and may broaden the range of MOFs usable under γ radiation in nuclear off-gas separation. These findings offer valuable molecular-level design insights.