Finely Controlled Stepwise Engineering of Pore Environments and Mechanistic Elucidation of Water-Stable, Flexible 2D Porous Coordination Polymers

Highly Efficient CO2 Capture from Wet-Hot Flue Gas by a Robust Trap-and-Flow Crystal

Highly selective CO2 capture from flue gas based on adsorption technology is among the largest challenge on the horizon, due to its high temperature (>333 K), lower partial pressure (0.1-0.2 bar), and competition from water. Due to the designable and tunable pore system, porous coordination polymers (PCPs) have been considered as the most exciting discoveries in porous materials. However, the rational design and function-led preparation of the pore system that permits highly selective CO2 capture from flue gas (CO2/N2/O2/CO/H2O) remains a great challenge. Herein, we report a highly selective CO2 capture from wet-hot (363 K, RH = 40%) flue gas by a robust trap-and-flow crystal (NTU-67). Crystallographic analysis showed that the flow channel provides plausible CO2 traffic, while the confined trap works as an accommodation for captured gas molecules. Further, the hydrophobic pore surface endows the function of the channels that are not influenced by hot moisture, a major obstacle to overcome direct CO2 capture by PCPs. The integral nature of NTU-67, including good stability in SO2, meets the key prerequisites that are usually considered for practical applications. The molecular insight and highly efficient CO2 capture make us believe that different nanospace with their own duties may be extended into ingenious design of more advanced adsorbents for cost-effective and promising for CO2 capture from flue gas.

Rotation configuration control of the sp2 bond in the diimidazole-dicarboxylate linker for the isomerism of porous coordination polymers

Porous isomers constructed from the same building blocks but different topology break the general preferred coordination rule of organic linkers and metal nodes, representing an invaluable opportunity for enriching their pore chemistry. Herein, a new group of porous isomers (termed as NTU-69 and NTU-70) was prepared from a C_2v symmetric diimidazole-dicarboxylate ligand and mononuclear Cu ion. The structural differences arise from the different rotation configuration of the sp² bond in the ligand, leading them to exhibit completely different topologies of unc (NTU-69) and sod (NTU-70) as well as framework rigidness. This rotation configuration of the sp² bond can be controlled by the different acidity of the synthetic solution and the metal/ligand ratio. Gas adsorption and IAST selectivity show that NTU-70 features high potential for CH₄ purification from C₂H₄, C₂H₆, C₃H₆ and CO₂ mixtures at room temperature. The insight from this work establishes a new bridge between the ligand design and controlled construction of porous isomers.

The synthesis of metal-organic frameworks with template strategies

The synthesis of metal-organic frameworks (MOFs) with a template strategy is still fascinating and has received considerable attention from structural chemists. In this review, developments in tuning MOF hosts or pore structures with a template strategy in the past decades are summarized. By adding templates into MOF precursors, novel template@MOF materials can always be obtained, which cannot be accessed by traditional synthesis procedures. Template@MOF materials can be structurally characterized to help understand the interactions between host frameworks and guest templates. On the other hand, changing the species or amount of template may lead to a pore structure change that can be used as a molecular container to load functional guest molecules with matching sizes for specific applications. It is hoped that this review will provide future researchers with new insight into the design and synthesis of MOF materials by applying suitable templates.

Optimized nanospace of coordination isomers with selenium sites for acetylene separation

Assisted by functional Cu and Se sites, a new group of porous isomers demonstrated systematically tunable C₂H₂/CO₂ separation.

Functionalized Dynamic Metal-Organic Frameworks as Smart Switches for Sensing and Adsorption Applications

Over the past two decades, metal-organic frameworks (MOFs) with flexible structures or dynamic behavior have shown great potential as functional materials in many fields. This paper presents a review of these dynamic and functional MOFs, which can undergo controllable and reversible transformation, with regard to their application as smart switches. Trigger conditions, which include physical/chemical stimuli (e.g., guest molecules, light, temperature, pressure), are also discussed. Research methods for investigating the dynamic processes and mechanisms involving experimental characterization and computational modeling are briefly mentioned as well. The emphasis is on the aspects of the design and functionalization of dynamic MOFs. The pre-design of metal nodes, organic linkers, and topology, as well as post-modification of components, increases the possibility of obtaining functionalized dynamic materials. Recent advances with regard to potential applications for dynamic frameworks as smart switches for adsorption and sensing are also reviewed.

Chemically Robust, Cu-based Porous Coordination Polymer Nanosheets for Efficient Hydrogen Evolution: Experimental and Theoretical Studies

Due to the extremely high number of accessible active sites and short diffusion path, porous coordination polymer (PCP) nanosheets have demonstrated a variety of promising applications, especially for energy conversion and mass transfer. However, the development of chemically stable PCP nanosheets with dense active sites and large lateral size is a great challenge in terms of feasible considerations. Herein, we first designed and prepared a kind of chemically stable PCP nanosheets via a bottom-up and a top-down integral strategy. Featuring densely exposed and periodic Cu²⁺ active sites (2.1 × 10⁶ per μm²), as well as ultrathin nature (5 nm) and significant pores (18 Å), this nanosheet demonstrated remarkable performance of electrocatalytic hydrogen evolution. Furthermore, one plausible process and the effect of Cu²⁺ active sites were proposed and validated by density functional theory calculations.

Enhanced Breakthrough Efficiency by a Chemically Stable Porous Coordination Polymer with Optimized Nanochannel

High separation efficiency is very important for process of pressure swing adsorption (PSA) in the industry. Herein, we propose a fine design of chemically stable porous coordination polymers (PCPs) with optimized nanochannel by strategy of inserting and shifting shortest alkyl group on T-shaped ligand. Remarkably, the synergistic effect of optimized nanochannel, unique crystal morphology and fitted channel enable sharply enhanced breakthrough efficiency of C₂H_6/4/CH₄, 1.17 or 0.77 g of CH₄ can be separated from corresponding dual mixtures (2/8, v/v) by 1 g of NTU-25 at 273 K, which was further validated and understood by controlled experiments and density functional theory (DFT) computations.

Near-Perfect CO2/CH4 Selectivity Achieved through Reversible Guest Templating in the Flexible Metal-Organic Framework Co(bdp)

Metal-organic frameworks are among the most promising materials for industrial gas separations, including the removal of carbon dioxide from natural gas, although substantial improvements in adsorption selectivity are still sought. Herein, we use equilibrium adsorption experiments to demonstrate that the flexible metal-organic framework Co(bdp) (bdp^2- = 1,4-benzenedipyrazolate) exhibits a large CO₂ adsorption capacity and approaches complete exclusion of CH₄ under 50:50 mixtures of the two gases, leading to outstanding CO₂/CH₄ selectivity under these conditions. In situ powder X-ray diffraction data indicate that this selectivity arises from reversible guest templating, in which the framework expands to form a CO₂ clathrate and then collapses to the nontemplated phase upon desorption. Under an atmosphere dominated by CH₄, Co(bdp) adsorbs minor amounts of CH₄ along with CO₂, highlighting the importance of studying all relevant pressure and composition ranges via multicomponent measurements when examining mixed-gas selectivity in structurally flexible materials. Altogether, these results show that Co(bdp) may be a promising CO₂/CH₄ separation material and provide insights for the further study of flexible adsorbents for gas separations.

Controlled flexibility of porous coordination polymers by shifting the position of the –CH3 group around coordination sites and their highly efficient gas separation

By adjusting the position of the methyl group, we found significant changes in the structural flexibility of the obtained PCPs, which also showed good gas separation ability.