Xiang-Jing Kong

Atmospheric water harvesting (AWH) can be enabled by solid desiccants that exhibit S‐shaped adsorption isotherms with one or more steps at low relative humidity (RH, SIFSIX‐3‐Ni family of hybrid coordination networks (HCNs) and a new, related family of HCNs, reveals a shared cooperative chemisorption mechanism with markedly different RH thresholds and regeneration requirements. Whereas the SIFSIX‐3‐Ni family operates outside the RH and regeneration limits of ROSs, four M′FSIX‐25‐M analogues (M = Co ²⁺ , Ni ²⁺ ; M' = Si ⁴⁺ , Ti ⁴⁺ , 25 = 1,4‐bis(imidazol‐1‐yl)naphthalene) exhibit both low‐RH chemisorption and regeneration from 34‐44°C. The lead regeneration optimized chemisorbent, ROC‐1 ( TIFSIX‐25‐Ni ), has a projected water‐harvesting productivity of ca. 3.5 L _sorbent ⁻¹ d ⁻¹ . Density functional theory calculations provide insight into the energetics and mechanism of hydration/dehydration in these first‐generation ROCs. This work establishes ROCs as a new class of desiccants that offers reversible chemisorption within the low‐RH and mild‐regeneration conditions relevant to AWH in arid environments.

Atmospheric water harvesting (AWH) can be enabled by solid desiccants that exhibit S‐shaped adsorption isotherms with one or more steps at low relative humidity (RH, SIFSIX‐3‐Ni family of hybrid coordination networks (HCNs) and a new, related family of HCNs, reveals a shared cooperative chemisorption mechanism with markedly different RH thresholds and regeneration requirements. Whereas the SIFSIX‐3‐Ni family operates outside the RH and regeneration limits of ROSs, four M′FSIX‐25‐M analogues (M = Co ²⁺ , Ni ²⁺ ; M' = Si ⁴⁺ , Ti ⁴⁺ , 25 = 1,4‐bis(imidazol‐1‐yl)naphthalene) exhibit both low‐RH chemisorption and regeneration from 34‐44°C. The lead regeneration optimized chemisorbent, ROC‐1 ( TIFSIX‐25‐Ni ), has a projected water‐harvesting productivity of ca. 3.5 L _sorbent ⁻¹ d ⁻¹ . Density functional theory calculations provide insight into the energetics and mechanism of hydration/dehydration in these first‐generation ROCs. This work establishes ROCs as a new class of desiccants that offers reversible chemisorption within the low‐RH and mild‐regeneration conditions relevant to AWH in arid environments.

Reticular chemistry enables construction of metal–organic frameworks (MOFs) with predictable topologies by matching the connectivity and geometry of nodes and linkers. However, extending such design principles to pyrazolate systems remains challenging due to the fixed connectivity and geometric directionality of their metal nodes, which limits structural diversity. Herein, we report a building-unit connectivity transposition approach that bridges these two coordination regimes by transposing the connectivity roles of linkers and metal nodes. An octatopic porphyrin-based pyrazolate ligand, 5,10,15,20-tetrakis(3,5-di(1H-pyrazol-4-yl)phenyl)porphyrin (H8TDPP), was designed to mimic the geometry of a typical D4h-symmetric Zr6 node in carboxylate frameworks, which can match the Oh-type Co4OPz6 cluster, affording three-dimensional frameworks BUT-59(M) (M = Co, Mn or Fe, where M denotes the metal incorporated into the porphyrin center). Single-crystal X-ray diffraction reveals a cubic structure composed of geometrically encoded 8-connected linkers and 6-connected metal clusters, representing the first ocu-a network among azolate MOFs. BUT-59 exhibits permanent porosity and chemical stability, maintaining its crystallinity and pore structure under strongly basic conditions. Featuring abundant accessible porphyrin–Co sites within its pores, BUT-59(Co) acts as an efficient heterogeneous catalyst for the Markovnikov-selective Wacker-type oxidation of styrenes under mild conditions. Its catalytic performance is comparable to that of homogeneous cobalt catalysts, while maintaining high recyclability without structural degradation. These results highlight the strength of connectivity role transposition in unlocking specific topological access in systems with geometrically constrained building units, thereby expanding the structural diversity and functionality of robust MOFs.

Electrocatalytic hydrogenation (e -H) provides a sustainable route for converting unsaturated organic substrates under mild conditions using renewable electricity as the driving force. Here, we report an MOF-derived cobalt catalyst for the e -H of acetone and pyridine. A new two-dimensional cobalt metal–organic framework, Co-L0-NS, composed of Co(II) nodes and polyaromatic carboxylate linkers, was synthesized as nanosheets and used as a precursor to generate the active catalyst under cathodic bias. Electrochemical pretreatment induces controlled framework reconstruction to form MD-Cat, a highly dispersed, structurally disordered, Co(OH)2-rich nanocluster material. MD-Cat catalyzes the e -H of acetone to isopropanol with nearly quantitative Faradaic efficiency at optimized potentials and promotes pyridine hydrogenation to piperidine with up to 50% Faradaic efficiency. Comparative studies with electrodeposited cobalt, commercial cobalt nanoparticles, and bulk Co(OH)2 show that the MOF-derived catalyst exhibits superior current densities and product selectivity, which we attribute to its nanoscale morphology and hydroxylated cobalt environment. In situ Co K-edge XAS, XPS, PXRD, ATR-SEIRAS, and STEM analyses indicate that Co remains predominantly in the +2 oxidation state during catalysis while undergoing structural reorganization. Tafel analysis supports a PCET-type mechanism for acetone hydrogenation; while DFT calculations suggest that the Co/Co(OH)2 interface suppresses HER by weakening H* binding while preserving organic-substrate activation. These results highlight MOF-templated electrochemical reconstruction as a promising approach for designing selective e -H catalysts, not only by increasing catalyst accessibility through nanostructuring but also by enabling the formation of unique catalytic motifs that would otherwise be difficult to access using traditional methods.

Conspectus: The development of adsorbents acting as “molecule traps” for advanced adsorption and separations on specific molecular recognition has garnered increasing attention over the past decade. Molecule trapping can be understood as strong confinement of guest molecules within well-defined local environments inside adsorbents, where adsorption is governed by geometric matching and multiple host–guest interactions rather than nonspecific van der Waals interactions alone. This site-specific trapping strategy enables precise discrimination between molecules with similar physicochemical properties under complex separation conditions. In particular, metal–organic frameworks (MOFs) provide an ideal platform for constructing molecule traps because their modular, designable, and crystalline structures enable the precise spatial organization of binding sites and confined pore environments. This Account highlights our recent advances in MOF-based molecule-trap adsorbents, from the foundational concept of the single-molecule trap to diverse trapping modes, including aromatic, localized, dynamic, and reactive trapping. These trapping modes enable selective recognition and capture/separation of hydrocarbons, greenhouse gases, and air pollutants through distinct confined interaction environments. Beyond empirical design, molecule trapping is also increasingly being guided by data-driven approaches, including large language model-assisted extraction of structure–function relationships and mechanism-based analysis. Furthermore, advances in scalable synthesis, material shaping, and continuous operation have moved MOF-based molecule-trap adsorbents closer to practical separation processes. These studies suggest that molecule trapping can serve as a useful design strategy for adsorption and separation media, providing a conceptual framework for the development of next-generation porous materials.

Achieving high crystallinity and controlled framework flexibility in covalent organic frameworks (COFs) remains a significant challenge for dynamic gas adsorption. Here we report a three-dimensional COF obtained through a single-crystal-to-single-crystal imine-to-amine linkage transformation that exhibits flexible yet robust adsorption behavior. A rigid imine-linked single-crystal COF (39-i) was converted into its amine-linked analogue (39-a) by postsynthetic Leuckart-Wallach reduction with formic acid, while preserving single crystallinity. Despite their identical topologies, 39-i and 39-a exhibit distinct structural responses during guest adsorption-desorption processes: 39-i retains its framework rigidity, whereas polar molecules (e.g., SO₂, H₂O, MeOH) induce pore-opening behavior in 39-a. PXRD indicates that 39-a undergoes a reversible transformation from a guest-stabilized crystalline phase to a distorted phase with reduced long-range order upon guest removal. Notably, 39-a achieves an exceptionally high SO₂ uptake of 10.4 mmol g^-1 at 298 K and 1 bar, representing one of the highest values reported for COFs under ambient conditions, despite exhibiting negligible N₂ uptake at 77 K. Experimental and computational analyses reveal that activation induces a folded state in 39-a, retaining guest-accessible volume prior to further pore expansion, with framework compression accommodated through cooperative folding and torsional distortion. In addition, the secondary amine linkages reduce the energetic penalty for framework deformation, allowing strong host-guest interactions with SO₂ to drive pore adaptation while preserving structural integrity during the reversible disorder-order-disorder transformation observed in SO₂ sorption. These findings establish linkage-controlled structural adaptation as a design strategy for dynamic gas adsorption in chemically aggressive environments.

Adsorbed natural gas storage using porous materials at ambient temperature and relatively low pressure promises to address safety and cost concerns of conventional natural gas storage technologies (liquefaction and compression), but its utility is hindered by low deliverable capacity. Flexible porous materials such as metal–organic frameworks can exhibit isotherms with the potential to afford enhanced deliverable capacity. However, prototypal flexible adsorbed natural gas sorbents, exemplified by the metal–organic framework cobalt benzenedipyrazolate, Co(bdp), suffer from hydrolytic instability and are unsuitable for pelletization. Here we report a family of metal–bipyrazolate frameworks, including hydrophobic sorbents, Zn(dpt) and Co(dpt) (H₂dpt = 2,5-di(1H-pyrazol-4-yl)thiophene), that exhibit methane-induced reversible transformations between narrow-pore and large-pore phases. Zn(dpt) shows exceptionally high methane deliverable capacities for 5–35 and 5–65 bar, that is, 173 cm³ (STP) cm⁻³ and 225 cm³ (STP) cm⁻³, respectively, but, unlike Co(bdp), is hydrolytically stable. In situ structural characterization, high-pressure gas sorption and modelling provide an insight into the narrow-pore–large-pore transformations, whereas testing with 250-ml tanks reveals that Zn(dpt) retains high deliverable capacity over multiple cycles. We demonstrate a practical alternative to pelletization through a formulation approach that is probably generally suitable for flexible sorbents.

Water vapor sorption in metal–organic frameworks (MOFs) is governed by a delicate interplay between framework topology, pore dimension, and distribution of water-binding sites. Isoreticular MOFs provide a powerful platform to disentangle these factors, yet direct comparisons that isolate the role of the metal node remain rare. Herein, we report a systematic study of water vapor adsorption in a family of fcu-type Ni₈-dipyrazolate frameworks, BUT-191–BUT-194 (BUT = Beijing University of Technology), constructed from a series of dipyrazolate ligands incorporating various heteroaromatic cores, including pyridyl, pyrimidyl, pyrazinyl, and pyridazinyl. All four Ni₈ frameworks exhibit exceptional chemical stability under harsh aqueous conditions. Water vapor sorption measurements at 298 K reveal pronounced S-shaped isotherms with steep uptake below ∼32% relative humidity (RH), with a maximum water uptake of up to 0.59 g g^–1. In contrast to previously reported isoreticular Co₈-dipyrazolate frameworks, no detectable redox transformation of the metal node is observed in the Ni₈ analogues during water sorption, enabling fully reversible adsorption–desorption behavior with excellent cycling stability. Particle size control experiments further reveal that hysteresis can be effectively suppressed without sacrificing the adsorption capacity, highlighting the role of mass transport in tuning water sorption reversibility. These findings provide fundamental insights into metal-node-dependent water sorption mechanisms in robust azolate MOFs, offering practical guidelines for the rational design of recyclable water vapor sorbents.

Zirconium-based metal-organic frameworks (Zr-MOFs) exhibit remarkable structural diversity and functionality. However, uncovering new topological types within this family remains a considerable challenge today. Herein, we report two new hexa-topic ligands designed through the introduction of torsional flexibility, which enable the construction of two Zr-MOFs featuring rare network topologies. The (4,4',4″,4‴,4‴',4‴''-((2-carboxybenzene-1,3,5-triyl)tris(9H-carbazole-9,3,6-triyl))hexabenzoic acid ligand (BTCH)) was obtained by replacing the rigid triptycene core in the H₆PET-1 ligand (4,4',4″,4‴,4‴',4‴''-(9,10-dihydro-9,10-[1,2]benzenoanthracene-2,3,6,7,14,15-hexayl)hexabenzoic acid) with a benzene-tricarbazole unit. Owing to its torsionally flexible core that allows rotational freedom to the arms, this ligand directs the construction of NU-2620 (NU represents Northwestern University), a Zr-MOF with 8-connected Zr₆ clusters and the rare nuh topology. Further flexibilization of the carbazole units to benzene rings yielded the even more torsionally flexible 5',5‴-bis(4-carboxyphenyl)-5″-(4,4″-dicarboxy-[1,1':3',1″-terphenyl]-5'-yl)-[1,1':3',1″:3″,1‴:3‴,1‴'-quinquephenyl]-4,4‴'-dicarboxylic acid ligand (CCTT), which forms NU-2630 featuring 6-connected clusters and the pcu topology. Both frameworks exhibit good chemical stability, prompting evaluation of their performance in CO₂ photoreduction catalysis. Under low-concentration CO₂ conditions, NU-2620 displays markedly higher catalytic activity than its benzene-based analogue, NU-2630, thanks to the abundance of photoactive carbazole units within its structure. These results demonstrate that introducing torsional flexibility in high-connected linkers can unlock access to new topologies and accelerates the reticular expansion of Zr-MOFs.