Flexible metal–organic frameworks for gas storage and separation

Li, Yue; Wang, Yu-Tong; Fan, Weidong; Sun, Daofeng

doi:10.1039/d1dt03842g

Cited by 93 publications

(53 citation statements)

References 102 publications

(106 reference statements)

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“…While flexible MOFs have caught more and more attention, − there is still a lack of comprehensive understanding of the thermodynamic/kinetic bases and roles (especially the advantages and disadvantages) for adsorptive separation. In the following sections, we will discuss these topics, focusing on guest-driven flexibility and gating flexibility, which are the most relevant types of TCF and KCF associated with adsorptive separation, respectively.…”

Section: Introductionmentioning

confidence: 99%

On the Role of Flexibility for Adsorptive Separation

Zhou

Zhang

2022

Acc. Chem. Res.

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Conspectus Chemical separations, mostly based on heat-driven techniques such as distillation, account for a large portion of the world’s energy consumption. In principle, differential adsorption is a more energy-efficient separation method, but conventional adsorbent materials are still not effective for many industry-relevant mixtures. Porous coordination polymers (PCPs), or metal–organic frameworks (MOFs), are attractive for their well-defined, designable, modifiable, and flexible structures connecting to various potential applications. While the importance of the structural flexibility of MOFs in adsorption-based functions has been demonstrated, the understanding of this special feature is still in its infancy and mostly stays at the periodic structural transformation at the equilibrium state and the special shapes of single-component adsorption isotherms. There are many confusions about the categorization and roles of various types of flexibility. This Account discusses the role of flexibility of MOFs for adsorptive separation, mainly from the thermodynamic and kinetic points of view. As the classic type of framework flexibility, guest-driven structural transformations and the corresponding adsorption isotherms can be thermodynamically described by the energies of the host–guest system. The highly guest-specific pore-opening action showing contrasting single-component adsorption isotherms is regarded as a strategy for achieving molecular sieving without the need for aperture size control, but its effect and role for mixture separation are still controversial. Quantitative mixture adsorption/separation experiments showed that the common periodic (cooperative) pore-opening action leads to coadsorption of molecules smaller than the opened aperture, while the aperiodic (noncooperative) one can achieve inversed molecular sieving under a thermodynamic mechanism. The energy barrier and structure in the nonequilibrium state are also important for flexibility and adsorption/separation. With suitable energy barriers between metastable structures, new types of framework flexibility such as aperture gating can be realized. While kinetically controlled gating flexibility is usually ignored because of the difficulty of characterization or considered as disadvantageous for separation because of the variable aperture size, it plays a critical role in most kinetic separation systems, including adsorbents conventionally regarded as rigid. With the concept of gating flexibility, the meanings of aperture and guest sizes for judging molecular sieving need to be reconsidered. Gating flexibility depends on not only the host itself but also the guest, the host–guest interaction, and the external environment such as temperature, which can be rationally tuned to achieve special adsorption/separation behaviors such as inversed temperature dependence, molecular sieving, and even inversed thermodynamic selectivity. The comprehensive understanding of the thermodynamic and kinetic bases of flexibility will give a new horizon for next-gener...

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Section: Introductionmentioning

confidence: 99%

On the Role of Flexibility for Adsorptive Separation

Zhou

Zhang

2022

Acc. Chem. Res.

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“…15–17 MOFs are emerging as a new type of porous crystalline hybrid materials for applications including gas storage, catalysis, drug delivery, and smart sensing. 18–21 Over the past few years, MOF-based fluorescence sensors have been widely used to detect ionic species, 22–25 small molecules, 26 volatile organic compounds (VOCs), 27 explosives, 28 and biologically relevant molecules and so on. 29–34…”

Section: Introductionmentioning

confidence: 99%

“…[15][16][17] MOFs are emerging as a new type of porous crystalline hybrid materials for applications including gas storage, catalysis, drug delivery, and smart sensing. [18][19][20][21] Over the past few years, MOF-based fluorescence sensors have been widely used to detect ionic species, [22][23][24][25] small molecules, 26 volatile organic compounds (VOCs), 27 explosives, 28 and biologically relevant molecules and so on. [29][30][31][32][33][34] The reaction of lanthanide ions and luminescent organic molecule ligands is an effective method to construct excellent MOF fluorescence sensors.…”

Section: Introductionmentioning

confidence: 99%

Stable terbium metal–organic framework with turn-on and blue-shift fluorescence sensing for acidic amino acids (l-aspartate and l-glutamine) and cations (Al³⁺ and Ga³⁺)

Ren

Zhang

et al. 2022

Dalton Trans.

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“…8,9 As a new class of metal-organic materials, coordination polymers (CPs), especially metal-organic frameworks (MOFs) are well-known for their high designability and porous structures, which play important roles in numerous applications, such as gas storage, adsorption, separation, fluorescence sensing, etc. [10][11][12][13] Photochromic CPs/MOFs can be assembled by introducing functional photochromic components (organic ligands, such as viologen, naphthalimides, and their derivatives). [14][15][16][17][18] Compared with conventional photochromic materials, three-dimensional (3D) extended networks prevent the accumulation of photoactive organic groups to some extent, effectively prolonging the retention time of photo-generated radicals.…”

Section: Introductionmentioning

confidence: 99%