Porosimetry of zeolitic imidazolate frameworks using positron annihilation lifetime spectroscopy

Mor, Jaideep; Utpalla, P.; Bahadur, Jitendra; Sen, Debasis; Sharma, S.K.

doi:10.1016/j.micromeso.2022.112389

Cited by 12 publications

(18 citation statements)

References 75 publications

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“…With the increase in phase transformation time, the good-quality ZIF-8 phase continuously increases in the frameworks, leading to enhancement in the o -Ps intensity corresponding to pore aperture site and cavities inside the frameworks. In addition, the o -Ps intensity corresponding to inter-crystal voids is also observed to increase (Figure c) significantly after 24 h of phase transformation time due to o -Ps diffusion to these pores from interior bulk Figure d shows the relative open volume fraction ( f v , %) of the frameworks calculated using o -Ps annihilation parameters through eq f normalv .25em ( % ) = ∑ j = 1 k 4 3 π R j 3 ( I j , o ‐ P s ) where k represents the type of pore sites present within the framework and R j corresponds to the radius of the pore assuming spherical shape and determined from the corresponding o -Ps lifetime using the Extended Tao Eldrup model, , I j (%) is the o -Ps intensity corresponding to the j th pore site within the framework.…”

Section: Resultsmentioning

confidence: 92%

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Evolution of Local Structure and Pore Architecture during Zeolitic Imidazolate Framework-L to Zeolitic Imidazolate Framework-8 Phase Transformation Investigated Using Raman, Extended X-ray Absorption, and Positron Annihilation Lifetime Spectroscopy

et al. 2023

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Zeolitic imidazolate framework-leaf (ZIF-L) is transformed to ZIF-8 through a topotactic phase transformation. This phase transformation is driven by the removal of the hydrogen-bonded linker molecules from 2D galleries of ZIF-L, leading to distortion in the hydrogen-bonded structure. Investigation of crystallization kinetics of ZIF-L shows that crystalline particles are formed within the first minute, and the growth of leaf-type structures is finished in nearly 10 minutes. During ZIF-L to ZIF-8 transformation, leaf-like ZIF-L particles are cleaved and transformed to 3D ZIF-8 nanocrystals. The chemical bonding structure investigated through Fourier transform infrared and Raman spectroscopy shows shifting and narrowing of characteristic peaks of stretching modes corresponding to linker molecules and Zn–N during the transformation. It confirms that distortions occur in the hydrogen-bonded structure of the ZIF-L phase. X-ray absorption spectroscopy shows modifications in the local structure around the Zn atom due to the reorientation of the fully bridged linker without affecting the Zn–N bond distances in the basic ZnN4 tetrahedral unit of ZIF-L or ZIF-8. Pore architecture evolution during the phase transformation is investigated by positron annihilation lifetime spectroscopy. During the transformation, the pores of ZIF-L are initially expanded with the decrease in their number density due to the breakdown of walls formed by intercalated linker molecules. With the increase in the ZIF-8 phase, the channel network of ZIF-8 sodalite topology along with inter-crystalline voids is gradually produced. A significant pore tuning of ZIF-L and ZIF-8 is achieved depending on the phase transformation time, which can be utilized for the enhancement in the gas separation efficiency of ZIF-8- or ZIF-L-based membranes.

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Section: Resultsmentioning

confidence: 92%

“…Figure 2a shows the XRD patterns of the as-synthesized ZIF-L, i.e., ZIF-L(0), and after its phase transformation for different times (3,6,24,40, and 72 h) along with a pure ZIF-8 sample.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Evolution of Local Structure and Pore Architecture during Zeolitic Imidazolate Framework-L to Zeolitic Imidazolate Framework-8 Phase Transformation Investigated Using Raman, Extended X-ray Absorption, and Positron Annihilation Lifetime Spectroscopy

et al. 2023

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“…It has been shown that ZIFs have flexible framework and the flexibility is dependent on crystal size, metal nodes, synthesis method etc. ,, In view of this, the difference observed in the average pore size determined from PALS with the theoretical values is attributed to the crystal size induced variation in flexibility and lattice defects produced during synthesis of bulk powder samples. However, it should be noted that PALS provides realistic values for pore sizes of ZIFs efficiently wherein most of the conventional gas adsorption techniques are found incapable for the same. The gas adsorption based methods do not work well for ZIFs primarily due to their ultramicroporosity and gas pressure induced gate opening phenomenon. , …”

Section: Resultsmentioning

confidence: 99%

Gate Opening Induced High Pore Volume Expansion in Flexible Zeolitic Imidazole Frameworks during CO₂ Adsorption: A Direct Observation Using Positron Annihilation Spectroscopy

et al. 2023

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Although Zeolitic Imidazolate Frameworks (ZIFs) show a great promise in the field of molecular separation owing to their crystalline morphology of pores, the sieving performance of ZIFs remains limited due to their flexible frameworks leading to “gate opening” phenomenon under gas pressure. However, the pore size expansion due to gate opening may ensure the use of flexible ZIFs as an efficient gas storage material at high pressure. In the present study, we have investigated the pore volume expansion in three flexible ZIFs (ZIF-8, ZIF-67, and ZIF-7) during CO2 adsorption up to high pressure ∼60 kg cm–2 using positron annihilation lifetime spectroscopy. Our result provides first direct in situ observation of pore volume expansion due to the gate opening in ZIF frameworks under high CO2 gas pressure. The enhancement in pore volume at all the available gas adsorption sites in these frameworks is caused due to the linker rotation and phase transformations. ZIF-8 framework flexibility was observed to be much higher as compared to its cobalt-based analogue, i.e., ZIF-67. ZIF-7 is observed to show two step pore volume expansions first in low pressure range and second in high pressure range. The low pressure transition corresponds to well-known ZIF-7(np) to ZIF-7(lp) phase transformation. The second step is observed to be associated with much higher expansion of pore volume and must be associated with a crystal structural transformation in ZIF-7. All the phase transformations observed under CO2 pressure up to 60 kg cm–2 at 298 K in ZIF-8, ZIF-67, and ZIF-7 are observed to be fully reversible. The present study suggests that positronium is a powerful probe for the in situ investigation of the changes in pore architecture of ZIFs during gas adsorption, which plays an important role for the application of these frameworks in high level gas storage.

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“…28−32 Figure S2 shows the typical PALS spectra of silica−PEI microspheres showing the long o-Ps lifetime components, confirming the porosity within the microspheres. All the spectra were fitted to the sum of four decaying exponentials using PALSfit, 27 out of which the first two are attributed to the intrinsic annihilation of p-Ps and free positron annihilation which do not carry any information about the pore network of the microspheres. The last two exponential decays are attributed to o-Ps annihilation from two different annihilation (pore) sites.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…PALS measurement for bulk PEI has also been carried out using the same spectrometer and positron source. The PALS spectra of all the microspheres were analyzed using PALSFit . According to the PALSFit algorithm, the PALS spectrum is fitted to the combination of decaying exponentials convoluted with the Gaussian resolution function of the spectrometer.…”

Section: Experimental Methodsmentioning

confidence: 99%

Interplay between the Pore Network Modifications and Dynamics of Confined Polyethyleneimine in Self-Assembled Polyethyleneimine–Silica Nanoparticle Microspheres

et al. 2023

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The CO2 adsorption performance of porous materials loaded with an amine-bearing functionality is determined by the pore network of porous adsorbents and the dynamics of the adsorbed polymeric chains bearing the amine functionality. Herein, we report the modifications in the pore network of evaporation-induced self-assembled microspheres of silica nanoparticles with varying loadings of polyethyleneimine (PEI) using positron annihilation lifetime spectroscopy (PALS) and small-angle X-ray scattering (SAXS). The dynamics of the loaded PEI in the pore network of microspheres have been investigated using temperature-dependent broadband dielectric spectroscopy. PALS investigation confirms microporosity at two different length scales available at the interparticle regions in pristine silica nanoparticle-based microspheres. With PEI loading through the self-assembly process, the pore size and pore volume accessed by PALS are observed to increase up to 20 wt % loading, followed by a decrease due to modification in the clustering behavior of nanoparticles and filling of pores with excess PEI. These variations are highly consistent with the nonmonotonic jamming of silica nanoparticles, as observed from SAXS analysis, arising due to complex interactions between silica nanoparticles and PEI. Both the segmental and localized relaxations of the adsorbed PEI are observed to slow down compared to bulk PEI due to the interactions with silica nanoparticles akin to polymer nanocomposites. The slowing down of the relaxations is consistent with the free-volume variations of the confined PEI determined using PALS. The segmental relaxation time of the loaded PEI in the microspheres varies nonmonotonically with the PEI content. The observations from complementary investigations unequivocally confirm that the packing behavior of silica nanoparticles in the evaporation-induced self-assembled microspheres is controlled by the PEI content. On the other hand, the dynamics of PEI confined within the pore network of the microsphere are determined by the clustering behavior of silica nanoparticles.

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Porosimetry of zeolitic imidazolate frameworks using positron annihilation lifetime spectroscopy

Cited by 12 publications

References 75 publications

Evolution of Local Structure and Pore Architecture during Zeolitic Imidazolate Framework-L to Zeolitic Imidazolate Framework-8 Phase Transformation Investigated Using Raman, Extended X-ray Absorption, and Positron Annihilation Lifetime Spectroscopy

Evolution of Local Structure and Pore Architecture during Zeolitic Imidazolate Framework-L to Zeolitic Imidazolate Framework-8 Phase Transformation Investigated Using Raman, Extended X-ray Absorption, and Positron Annihilation Lifetime Spectroscopy

Gate Opening Induced High Pore Volume Expansion in Flexible Zeolitic Imidazole Frameworks during CO₂ Adsorption: A Direct Observation Using Positron Annihilation Spectroscopy

Interplay between the Pore Network Modifications and Dynamics of Confined Polyethyleneimine in Self-Assembled Polyethyleneimine–Silica Nanoparticle Microspheres

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Porosimetry of zeolitic imidazolate frameworks using positron annihilation lifetime spectroscopy

Cited by 12 publications

References 75 publications

Evolution of Local Structure and Pore Architecture during Zeolitic Imidazolate Framework-L to Zeolitic Imidazolate Framework-8 Phase Transformation Investigated Using Raman, Extended X-ray Absorption, and Positron Annihilation Lifetime Spectroscopy

Evolution of Local Structure and Pore Architecture during Zeolitic Imidazolate Framework-L to Zeolitic Imidazolate Framework-8 Phase Transformation Investigated Using Raman, Extended X-ray Absorption, and Positron Annihilation Lifetime Spectroscopy

Gate Opening Induced High Pore Volume Expansion in Flexible Zeolitic Imidazole Frameworks during CO2 Adsorption: A Direct Observation Using Positron Annihilation Spectroscopy

Interplay between the Pore Network Modifications and Dynamics of Confined Polyethyleneimine in Self-Assembled Polyethyleneimine–Silica Nanoparticle Microspheres

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Gate Opening Induced High Pore Volume Expansion in Flexible Zeolitic Imidazole Frameworks during CO₂ Adsorption: A Direct Observation Using Positron Annihilation Spectroscopy