Molecular Sieving of Propyne/Propylene by a Scalable Nanoporous Crystal with Confined Rotational Shutters

Metal-organic framework with pore contraction and modification by diethylammonium cations for record SO2/CO2 separation

A robust MOF with diethylammonium cations in its pores, enhances pore partitioning and modifies the environment, enabling selective and dense SO2 packing through hydrogen bonds. It achieves a reversible SO2 uptake with a high adsorption enthalpy and record IAST selectivity of 1182 for SO2/CO2 at 298 K and 1 bar.

Systemic regulation of binding sites in porous coordination polymers for ethylene purification from ternary C2 hydrocarbons

The global demand for poly-grade ethylene (C2H4) is increasing annually. However, the energy-saving purification of this gas remains a major challenge due to the similarity in molecular properties among the ternary C2 hydrocarbons. To address this challenge, we report an approach of systematic tuning of the pore environment with organic sites (from -COOH to -CF3, then to -CH3) in porous coordination polymers (PCPs), of which NTU-73-CH3 shows remarkable capability for the direct production of poly-grade C2H4 from ternary C2 hydrocarbons under ambient conditions. In comparison, the precursor structure of NTU-73-COOH is unable to purify C2H4, while NTU-73-CF3 shows minimal ability to harvest C2H4. This is because the changed binding sites in the NTU-73-series not only eliminate the channel obstruction caused by the formation of gas clusters, but also enhance the interaction with acetylene (C2H2) and ethane (C2H6), as validated by in situ crystallographic and Raman analysis. Our findings, in particular the systematic tuning of the pore environment and the efficient C2H4 purification by NTU-73-CH3, provide a blueprint for the creation of advanced porous families that can handle desired tasks.

Relay Adsorption in Metal-Organic Frameworks for One-Step Helium Purification at Ambient Temperature

One-step He purification from natural gas represents a crucial solution for addressing the global He shortages. The prevailing method to produce high-grade He involves cryogenic distillation and ultralow temperature adsorption processes, which is highly cost- and energy-intensive. Separating and purifying He at ambient temperature is a great challenge because the fundamental limitation lies in the boiling point, polarizability, and kinetic diameters of CH4/N2/He gases. In this study, we seek to implement a relay adsorption strategy using Ni(ina)2 and MIL-100(Cr) metal-organic frameworks (MOFs) to produce high-purity He from ternary mixtures (CH4, N2, and He) at ambient temperature. The CH4/He selectivity in Ni(ina)2 and N2/He selectivity in MIL-100(Cr) both reach record 15.39 and 128.49, respectively, making the relay adsorption for helium purification highly efficient. The breakthrough experiments show that the two MOFs can sequentially adsorb CH4 and N2 in ternary mixtures, producing He with a purity of up to 99.99% in one step. The remarkable separation performance and stability of these MOFs underscore the industrial potential in purifying He at ambient temperature.

A Zeolitic Octahedral Metal Oxide with Ultrahigh Porosity for High-temperature and High-humidity Alkyne/Alkene Separation

Zeolitic octahedral metal oxide is a newly synthesized all-inorganic zeolitic material and has been used for adsorption, separation, and catalysis. Herein, a new zeolitic octahedral metal oxide was synthesized and characterized. The porous framework was established through the assembly of [P2Mo13O50] clusters with PO4 linkers. Guest molecules occupied the framework, which could be removed through heat treatment, thereby opening the micropores. The pore characteristics were controlled by the cations within the micropore, enabling the adjustment of the interactions with alkynes and alkenes. This resulted in good separation performance of ethylene/acetylene and propylene/propyne even under high temperature and humidity conditions. The high stability of the material enabled the efficient recovery and reuse without discernible loss in the separation performance. Due to the relatively weak interaction between the adsorbed alkyne and the framework, the adsorbent facilitated the recovery of a highly pure alkyne. This feature enhances the practical applicability of the material in various industrial processes.

Solvents regulate the packing porosity of a bilayer metal-organic cage

Metal-organic cages (MOCs) are an emerging class of porous materials with promising applications. However, controlling the configuration of the cage packing, which can influence the overall porosity of the materials, remains a difficulty, as many factors can influence the cage assembly and stacking. Herein, we report a solvent strategy to fine-tune the packing configuration of a bilayer MOC, a small triangular prism cage (six Cu ions act as vertices, three nitrate ions act as pillars, and six nitrate ions act as caps) incorporated into a large triangular prism cage (another six Cu ions act as vertices, a couple of oxygen atoms act as pillars and six ligands (L1: 3,5-bis(pyridine-3-yl)-4H-1,2,4-triazole) act as a jointed cap) by the coordination between the triazole nitrogen from L1 and the inner vertex Cu ions. The involved solvents water, acetonitrile (MeCN) and N,N'-dimethylformamide (DMF) form hydrogen bonds with this bilayer MOC, resulting in three different types of packing associated with systemically tuned porosity (NTU-93: 12.2%, NTU-94: 19.3%, and NTU-95: 42.1%). Gas adsorption and breakthrough tests demonstrate that NTU-95 has potential ability for C2H2/C2H4 separation. This work not only shows a case of finely tuned packing of coordination cages, but also provides a powerful tool that may be extended to other cage families.

Immobilization of Amino-site into a Pore-Partitioned Metal-Organic Framework for Highly Efficient Separation of Propyne/Propylene

Adsorptive separation of propyne/propylene (C3H4/C3H6) is a crucial yet complex process, however, it remains a great difficulty in developing porous materials that can meet the requirements for practical applications, particularly with an exceptional ability to bind and store trace amounts of C3H4. Functionalization of pore-partitioned metal-organic frameworks (ppMOFs) is methodically suited for this challenge owing to the possibility of dramatically increasing binding sites on highly porous and confined domains. We here immobilized Lewis-basic (-NH2) and Lewis-acidic (-NO2) sites on this platform. Along with an integrated nature of high uptake of C3H4 at 1 kPa, high uptake difference of C3H4-C3H6, moderated binding strength, promoted kinetic selectivity, trapping effect and high stability, the NH2-decorated ppMOF (NTU-100-NH2) can efficiently produce polymer-grade C3H6 (99.95 %, 8.3 mmol ⋅ g-1) at room temperature, which is six times more than the NO2-decorated crystal (NTU-100-NO2). The in situ infrared spectroscopy, crystallographic analysis, and sequential blowing tests showed that the densely packed amino group in this highly porous system has a unique ability to recognize and stabilize C3H4 molecules. Moving forward, the strategy of organic functionalization can be extended to other porous systems, making it a powerful tool to customize advanced materials for challenging tasks.

Fine-regulation of gradient gate-opening in nanoporous crystals for sieving separation of ternary C3 hydrocarbons

The adsorptive separation of ternary propyne (C3H4)/propylene (C3H6)/propane (C3H8) mixtures is of significant importance due to its energy efficiency. However, achieving this process using an adsorbent has not yet been accomplished. To tackle such a challenge, herein, we present a novel approach of fine-regulation of the gradient of gate-opening in soft nanoporous crystals. Through node substitution, an exclusive gate-opening to C3H4 (17.1 kPa) in NTU-65-FeZr has been tailored into a sequential response of C3H4 (1.6 kPa), C3H6 (19.4 kPa), and finally C3H8 (57.2 kPa) in NTU-65-CoTi, of which the gradient framework changes have been validated by in situ powder X-ray diffractions and modeling calculations. Such a significant breakthrough enables NTU-65-CoTi to sieve the ternary mixtures of C3H4/C3H6/C3H8 under ambient conditions, particularly, highly pure C3H8 (99.9%) and C3H6 (99.5%) can be obtained from the vacuum PSA scheme. In addition, the fully reversible structural change ensures no loss in performance during the cycling dynamic separations. Moving forward, regulating gradient gate-opening can be conveniently extended to other families of soft nanoporous crystals, making it a powerful tool to optimize these materials for more complex applications.

Microporous Coordination Polymers for Efficient Recovery of Chloromethane from Organic Silicon Industrial Exhaust Gas

Removal and recovery of methyl chloride (CH3Cl) from exhaust gas of organic silicon industry is highly important from the perspective of environment and economy. For the first time, a tailor-made microporous coordination polymer (Mn-BDC-TPA) was synthesized and applied to the efficient capture and recovery of CH3Cl from related gas mixtures. The high adsorption capacity of CH3Cl (163.4 cm3/g) and high adsorption selectivity of CH3Cl over other impurity gases (1965 for N2, 65 for CH4, and 16 for C2H6) were achieved at 298 K and 100 kPa due to the dual-cage pore system and larger polarizability of CH3Cl. Dynamic breakthrough experiments demonstrate the excellent CH3Cl recovery performance (capacity of >98 cm3/g and purity of >95%) in one adsorption-desorption cycle from the CH3Cl-involved binary, ternary, or quaternary gas mixture.

Tuning Multiple Counter-Anions in Porous Coordination Polymers with Topology for Acetylene/Ethylene Separation

The efficient separation of acetylene (C2H2) and ethylene (C2H4) is an important and complex process in the industry. Herein, we report a new family of lcy-topologic coordination frameworks (termed NTU-90 to NTU-92) with Cu3MF6 (M = Si, Ti, and Zr) nodes. These charged frameworks are compensated by different counterbalanced ions (MF62-, BF4-, and Cl-), yielding changes in the size of the window apertures. Among these frameworks, NTU-92-a (activated NTU-92) shows good adsorption selectivity of C2H2/C2H4 and also significant ability in recovering both highly pure C2H4 (99.95%) and C2H2 (99.98%). Our work not only presents a potential alternative for energy-saving purification of C2 hydrocarbons but also provides a new approach for tuning the function of charged porous materials.