Gating effect for gas adsorption in microporous materials—mechanisms and applications

Chen, Kaifei; Mousavi, Seyed Hesam; Singh, Ranjeet; Snurr, Randall Q.; Li, Gang; Webley, Paul A.

doi:10.1039/d1cs00822f

Cited by 46 publications

(30 citation statements)

References 188 publications

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“…Based on the obtained rate constants of 8.2 × 10 −1 , 9.3 × 10 −2 , and 4.4 × 10 −2 g mmol −1 min −1 for pX, mX, and oX, respectively, the kinetic selectivity was calculated as k pX /k mX / k oX = 18.6/2.1/1 (Figure S14 and Table S2). The adsorption of the xylene mixtures achieved over 90% capacity of the equilibrium amount within 15 min, which was similar with [39]that of single-component pX (Figure 2c and Figure S12), indicating high kinetic selectivity for pX under mixture conditions. It is worth to note that the pX adsorption equilibrium time of MAF-89 (near room temperature) is one of the shortest among MOFs, zeolites and activated carbons [4,48], just longer than those of a handful of MOFs and PMCs [20,21], such as MAF-36 with small particle size of 0.5 μm × 0.5 μm × 1 μm [22].…”

Section: Resultssupporting

confidence: 71%

“…While many thermodynamic, kinetic, and even molecularsieving separation mechanisms have been reported [23][24][25][26], only ultramicropores with sizes similar to that of pX achieved high pX selectivity over 10 [2,3,21,22,27-34]. The size/shape-matched pores can achieve better guest recognition, while the ultra-small pore apertures enlarge the difference of guest adsorption/diffusion rates through the gating mechanism (transisent opening/closing of relatively small pore apertures), although these structural responses are often ignored due to the difficulty of characterization [22,23,[35][36][37][38][39]. However, such adsorbents generally possess discrete (0D) or one-dimensional (1D) pores with low porosities (void ratio < 20%) and high gating barriers (relatively rigid), giving low adsorption capacities (< 2.0 mmol g −1…”

Section: Introductionmentioning

confidence: 99%

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A gating ultramicroporous metal-organic framework showing high adsorption selectivity, capacity and rate for xylene separation

Zhang

Liu

et al. 2022

Sci. China Chem.

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Adsorptive separation of p-xylene (pX) from xylene isomers is a key process in chemical industry, but known adsorbents cannot simultaneously achieve high adsorption selectivity, capacity, and rate. Here, we demonstrate gating ultramicropore as a solution for this challenge. Slight modification of the synthetic condition gives rise to isomeric metal-organic frameworks α-[Zn(pba)] (MAF-88, H 2 pba = 4-(1H-pyrazol-4-yl)benzoic acid) and β-[Zn(pba)] (MAF-89) possessing similar pillared-column structures, porosities, and high pX capacities of 2.0 mmol g −1 , but very different framework/pore topologies, pore sizes, and pX selectivities. For binary and ternary mixtures of liquid xylene isomers, MAF-88 with narrow one-dimensional (1D) channels shows pX selectivity of 11 and 1.6, while MAF-89 with 3D-connected quasi-discrete pores shows pX selectivity up to 221 and 46, respectively. Thermogravimetry, differential scanning calorimetry, and time-dependent separation experiments reveal that the kinetic effects of the gating pores play more important roles than the thermodynamic effects, which is further confirmed by single-crystal X-ray diffraction and computational simulations.

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Section: Resultssupporting

confidence: 71%

Section: Introductionmentioning

confidence: 99%

A gating ultramicroporous metal-organic framework showing high adsorption selectivity, capacity and rate for xylene separation

Zhang

Liu

et al. 2022

Sci. China Chem.

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“…32,52,169,255,256 These structure changes can affect the adsorption properties of a material, in which case they are generally referred to as gating effects. 257 In the case of zeolites, two types of gating effects have been reported to be especially relevant, i.e., trapdoor phenomena and guest-induced framework deformation. "Trapdoor" zeolites involve a specific case of cation relocation in which the interaction of a specific molecule with an initially pore-blocking cation leads to a displacement of the cation and subsequent penetration of the molecule inside the pores.…”

Section: Chemical Reviewsmentioning

confidence: 99%

Zeolites in Adsorption Processes: State of the Art and Future Prospects

2022

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Zeolites have been widely used as catalysts, ion exchangers, and adsorbents since their industrial breakthrough in the 1950s and continue to be state-of the-art adsorbents in many separation processes. Furthermore, their properties make them materials of choice for developing and emerging separation applications. The aim of this review is to put into context the relevance of zeolites and their use and prospects in adsorption technology. It has been divided into three different sections, i.e., zeolites, adsorption on nanoporous materials, and chemical separations by zeolites. In the first section, zeolites are explained in terms of their structure, composition, preparation, and properties, and a brief review of their applications is given. In the second section, the fundamentals of adsorption science are presented, with special attention to its industrial application and our case of interest, which is adsorption on zeolites. Finally, the state-of-the-art relevant separations related to chemical and energy production, in which zeolites have a practical or potential applicability, are presented. The replacement of some of the current separation methods by optimized adsorption processes using zeolites could mean an improvement in terms of sustainability and energy savings. Different separation mechanisms and the underlying adsorption properties that make zeolites interesting for these applications are discussed.

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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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Gating effect for gas adsorption in microporous materials—mechanisms and applications

Abstract: External stimuli or host–guest interactions induce structural changes, producing a gating effect in which an adsorbent suddenly becomes accessible to guest molecules. This effect greatly facilitates gas separation, storage, and molecular detection.

Cited by 46 publications

References 188 publications

A gating ultramicroporous metal-organic framework showing high adsorption selectivity, capacity and rate for xylene separation

A gating ultramicroporous metal-organic framework showing high adsorption selectivity, capacity and rate for xylene separation

Zeolites in Adsorption Processes: State of the Art and Future Prospects

On the Role of Flexibility for Adsorptive Separation

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