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Developing energy‐efficient alternatives for propylene (C3H6) and propane (C3H8) separation is of great significance and challenge in the petrochemical industry. Herein, we report the rational design of a new yttrium‐based ultramicroporous metal–organic framework (MOF) comprised of 12‐connected hexanuclear [Y6(OH)8(COO)12]2− cluster and 5‐(3,5‐dicarboxybenzoylamino)isophthalic acid (H4dbai) with ftw topology. It possesses a suitable pore window size and a relatively large pore volume for molecular sieving separation of C3H8 from C3H6 with a high C3H6 capacity. At 298 K and 100 kPa, the adsorption capacity of C3H6 was 2.57 mmol/g, which is the highest among the reported C3H6/C3H8 molecular sieving MOF adsorbents. The molecular simulation revealed that the steric hindrance effect together with the electrostatic interaction of the oxygen sites in the window resulted in the molecular sieving separation of C3H6/C3H8. The breakthrough experiments confirmed its excellent separation performance under dynamic conditions to produce high purity (97.1%) of C3H6 with a working adsorption capacity of 1.75 mmol/g. [ABSTRACT FROM AUTHOR]

Metal‐organic frameworks (MOFs) show great potential for adsorption separation. However, MOFs' flexibility may influence their adsorption behaviors. Here, for the first time we prepare ZIF‐8 powder dominated with stiffened ZIF‐8_Cm phase under an external E‐field. By comparison, we find that the flexibility of ZIF‐8 has little influence in equilibrium‐based separation behavior for C3H6/C3H8. However, the stiffened ZIF‐8 formed in E‐field presents an obviously decreased diffusion rate for C3H8, whose C3H6/C3H8 kinetic‐based separation factor is around 2.5 times higher than that of the traditional ZIF‐8 powder. [ABSTRACT FROM AUTHOR]

The developments of high‐performance adsorbents have attracted ever‐increasing attention in the separation of ethane/ethylene (C2H6/C2H4) mixtures. In this work, a series of ultra‐stable C2H6‐selective metal–organic frameworks (MOFs), PCN‐250, and its bimetal version PCN‐250(Fe2M2+, M2+ = Ni2+, Co2+, Zn2+, Mn2+), were synthesized to investigate the influence of metal compositions on the C2H6‐selective performance. Among the five materials, at 298 K and 100 kPa, PCN‐250(Fe2Co) showed the largest C2H6 uptake (6.21 mmol/g) while PCN‐250(Fe2Zn) exhibited the highest C2H6/C2H4 ideal adsorption solution theory (IAST) selectivity (1.70). The molecular simulation revealed that the introduced metal ions have different influences on the atomic partial charge within the framework which varied the framework adsorption affinities toward C2H6/C2H4 molecules. Moreover, the research on PCN‐250(Fe2Zn) suggested that the increased positive partial charge of metal sites together with a decreased charge density of benzene ring (BR) sites from the organic ligands will be beneficial to improve the desired C2H6 selectivity. [ABSTRACT FROM AUTHOR]

Selectively separating CH4 from N2 in coal‐mine methane is significantly important in the chemical industry, but challenging and energy‐intensive. Using porous materials as adsorbents can separate CH4/N2 mixtures with low energy consumption, but most adsorbents encounter the problem of poor separation selectivity. Here, we propose a strategy for improving CH4/N2 selectivity by controlling pore wall environment in two isomeric Al‐based metal–organic frameworks (MOFs) with four highly symmetric polar sites for strengthened adsorption affinity toward CH4 over N2. At 298 K and 100 kPa, CAU‐21‐BPDC with four highly symmetric polar sites in the pore walls exhibits 2.4 times higher CH4/N2 selectivity than CAU‐8‐BPDC without four highly symmetric polar sites. Gas adsorption isotherms, CH4/N2 selectivity calculations, Qst of CH4, interaction energy calculations, adsorption density distributions of CH4 and N2, and breakthrough curves reveal that CAU‐21‐BPDC is a potential candidate for selective capture coal‐mine methane. [ABSTRACT FROM AUTHOR]

Given the fact that solvothermal synthesis is the most common synthetic method to obtain metal–organic frameworks (MOFs) on a gram scale, it still remains a great challenge to produce MOFs in a scalable and sustainable synthetic process. In this work, we develop a facile and rapid synthesis of copper-based MOF-505 by the exploitation of layered (Zn,Cu) hydroxy double salt as the intermediate for efficient MOF-505 crystallization at room temperature, in which [(Zn,Cu)(OH)NO3] is synthesized by reacting ZnO with Cu(NO3)2. Under an optimized reaction time of 25 min, MOF-505-25 exhibits a Brunauer–Emmett–Teller (BET) surface area of 1076 m2 g−1 and the pore size is narrowly distributed at 5.9 and 8.0 Å. With respect to CO2 adsorption and separation performance, MOF-505-25 shows a moderate CO2 uptake of 3.51 mmol g−1 at 298 K and 100 kPa and high CO2/CH4 and CO2/N2 adsorption selectivities of 7 and 29. Particularly, the formation of MOF-505 can be completed within a short reaction time (less than 30 min) whilst maintaining high quality. This facile and rapid room temperature synthetic procedure would pave the way for promoting the development of MOF materials large-scale production with minimizing the energy input. [ABSTRACT FROM AUTHOR]

Developing metal-organic frameworks (MOFs) with moisture-resistant feature or moisture-enhanced adsorption is challenging for the practical CO 2 capture under humid conditions. In this work, under humid conditions, the CO 2 adsorption behaviors of two iron-based MOF materials, PCN-250(Fe 3 ) and PCN-250(Fe 2 Co), were investigated. An interesting phenomenon is observed that the two materials demonstrate an unusual moisture-enhanced adsorption of CO 2 . For PCN-250 frameworks, H 2 O molecule induces a remarkable increase in the CO 2 uptake for the dynamic CO 2 capture from CO 2 /N 2 (15:85) mixture. For PCN-250(Fe 3 ), its CO 2 adsorption capacity increases by 54.2% under the 50% RH humid condition, compared with that under dry conditions (from 1.18 to 1.82 mmol/g). Similarly, the CO 2 adsorption uptake of PCN-250(Fe 2 Co) increases from 1.32 to 2.23 mmol/g, exhibiting a 68.9% increase. Even up to 90% RH, for PCN-250(Fe 3 ) and PCN-250(Fe 2 Co), obvious increases of 43.7 and 70.2% in the CO 2 adsorption capacities are observed in comparison with those under dry conditions, respectively. Molecular simulations indicate that the hydroxo functional groups (μ 3 -O) within the framework play a crucial role in improving CO 2 uptake in the presence of water vapor. Besides, partial substitution of Fe 3+ by Co 2+ ions in the PCN-250 framework gives rise to a great improvement in CO 2 adsorption capacity and selectivity. The excellent moisture stability (stable even after exposure to 90% RH humid air for 30 days), superior recyclability, as well as moisture-enhanced feature make PCN-250 as an excellent MOF adsorbent for CO 2 capture under humid conditions. This study provides a new paradigm that PCN-250 frameworks can not only be moisture resistant but can also subtly convert the common negative effect of moisture to a positive impact on improving CO 2 capture performance.