Identifying UiO‐67 Metal‐Organic Framework Defects and Binding Sites through Ammonia Adsorption

Devulapalli, Venkata Swaroopa Datta; McDonnell, Ryan P; Ruffley, Jonathan P.; Shukla, Priyanka B.; Luo, Tian‐Yi; Souza, Mattheus De; Das, Prasenjit; Rosi, Nathaniel L.; Johnson, J. Karl; Borguet, Eric

doi:10.1002/cssc.202102217

Cited by 10 publications

(9 citation statements)

References 95 publications

(84 reference statements)

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“…The C–H···N hydrogen bonds are formed by electrostatic attractions between the lone pair electrons of the nitrogen atom and the H atoms of acetylene molecules. Similarly, electrostatic attractions between the H atoms of ammonia and the electron-rich π-system of a neighboring acetylene molecule give rise to N–H···π hydrogen bonds. − These C–H···N and N–H···π interactions play a crucial role in determining the structure and dynamics of the acetylene:ammonia (1:1) co-crystal.…”

Section: Resultsmentioning

confidence: 99%

Molecular Structure, Dynamics, and Vibrational Spectroscopy of the Acetylene:Ammonia (1:1) Plastic Co-Crystal at Titan Conditions

Thakur

Remsing

2023

ACS Earth Space Chem.

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The Saturnian moon Titan has a thick, organic-rich atmosphere, and condensed phases of small organic molecules are anticipated to be stable on its surface. Of particular importance are crystalline phases of organics, known as cryominerals, which can play important roles in surface chemistry and geological processes on Titan. Many of these cryominerals could exhibit rich phase behavior, especially multicomponent cryominerals whose component molecules have multiple solid phases. One such cryomineral is the acetylene:ammonia (1:1) co-crystal, and here we use density functional theory-based ab initio molecular dynamics simulations to quantify its structure and dynamics at Titan conditions. We show that the acetylene:ammonia (1:1) co-crystal is a plastic co-crystal (or rotator phase) at Titan conditions because the ammonia molecules are orientationally disordered. Moreover, the ammonia molecules within this co-crystal rotate on picosecond time scales, and this rotation is accompanied by the breakage and reformation of hydrogen bonds between the ammonia hydrogens and the π-system of acetylene. The robustness of our predictions is supported by comparing the predictions of two density functional approximations at different levels of theory, as well as through the prediction of infrared and Raman spectra that agree well with experimental measurements. We anticipate that these results will aid in understanding geochemistry on the surface of Titan.

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Section: Resultsmentioning

confidence: 99%

Molecular Structure, Dynamics, and Vibrational Spectroscopy of the Acetylene:Ammonia (1:1) Plastic Co-Crystal at Titan Conditions

Thakur

Remsing

2023

ACS Earth Space Chem.

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“…82 To determine if this process occurs, we compare the line shape of ν(OH) free before, during, and after CD 3 CN exposure (Figure S18). The ν(OH) free line shape, reported to be a combination of both μ 3 -OH and isolated H 2 O species, 22,30 is initially symmetric and becomes slightly asymmetric following CD 3 CN desorption (blue trace, Figure S18). The induced asymmetry suggests that CD 3 CN successfully displacing a small fraction of H 2 O ligands.…”

Section: ■ Experimental Sectionmentioning

confidence: 99%

“…700 K. 25 Dehydroxylation occurs by heating UiO-67 between ca. 500 and 600 K. 22,25 It has additionally been reported that under ambient conditions, thermally activated UiO-66 MOFs have a higher density of defect sites. 26,27 Since UiO-66 and UiO-67 share identical nodal structures and differ primarily by the identity of the linker molecule, 28 thermal activation of UiO-67 should show a similar response.…”

Section: ■ Introductionmentioning

confidence: 99%

“…The chemistry of defective UiO-67 is well reported. − The most common type of defect in UiO-67 is the loss of BPDC linkers, which may yield coordinatively unsaturated Zr 4+ Lewis acid sites depending on the capping groups. , Defect concentration is typically engineered via manipulating the temperature of MOF synthesis, modulator choice, and concentrations . Defects are unavoidable even in the most optimized MOF synthetic process and are suggested to be the locus of catalytic activity in MOFs. ,,,− This catalytic activity is generally assigned to the increase in density of catalytic sites in a MOF and porosity, which enables the diffusion of reactants (and products) toward (and away from) active sites.…”

Section: Introductionmentioning

confidence: 99%

“…Defect concentrations in UiO MOFs are typically quantified via thermogravimetric analysis (TGA) (Figure S1). , Defects can also be characterized via a variety of methods, including X-ray diffraction, temperature-programmed desorption mass spectrometry (TPD-MS), in situ Fourier transform infrared (FT-IR) spectroscopy, temperature-programmed FT-IR (TP-IR). ,,,, While defects and active sites are present on a MOF exterior, catalysis is largely dependent on internal sites and hence internal defects . Thus, characterization of the internal sites in porous MOFs is essential to obtain an understanding of the MOF defect concentration.…”

Section: Introductionmentioning

confidence: 99%

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Anomalous Infrared Intensity Behavior of Acetonitrile Diffused into UiO-67

McDonnell,

Devulapalli,

Choi

et al. 2023

Chem. Mater.

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UiO-67 metal–organic frameworks (MOFs) show promise for use in a variety of areas, especially in industrial chemistry, as stable and customizable catalyst materials often driven by catalytically active defects (coordinatively unsaturated metal sites) present within the MOF crystallite. Thermal activation, or postsynthetic thermal treatment, of MOFs is a seldom used method to induce catalytically active defects. To investigate the effect of thermal activation on defect concentration in UiO-67, we performed Fourier transform infrared (FT-IR) spectroscopy studies of adsorbed CD3CN, a versatile infrared active probe molecule. Our results suggest that, under cryogenic, ultrahigh-vacuum conditions, CD3CN must be thermally diffused into UiO-67 to successfully detect binding sites and defects. Below dehydroxylation temperatures, blueshifted ν(CN) modes of diffused CD3CN indicate multiple avenues of hydrogen bonding within UiO-67, as well as binding to Lewis acid sites, assigned to be coordinately undersaturated Zr4+, consistent with in situ FT-IR of adsorbed CO. FT-IR of CD3CN diffused into UiO-67 activated to 623 K shows that while thermal activation eliminates hydrogen-bonding moieties, it also induces stronger Lewis acid sites, identified by a blueshifted ν(CN) doublet. Through density functional theory (DFT) calculations, we demonstrate that the ν(CN) doublet is a result of CD3CN interacting with two distinct nodal defect sites present in dehydroxylated UiO-67. Additionally, the infrared cross sections of CD3CN's ν(CN), ν(CD)s and ν(CD)as modes change, primarily due to hydrogen bonding, when diffused into UiO-67, as confirmed through DFT calculations. The nonlinear IR cross section behavior suggests that the Beer–Lambert law cannot trivially extrapolate the concentration of an analyte diffused into a MOF. These studies reveal the impact of postsynthetic thermal treatment on the concentration and type of Lewis acid defects in UiO-67 and caution the simple use of integrated infrared absorbance as a metric of analyte concentration within a MOF.

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Fine‐Tuning Porous Structure of Zirconium‐Based Metal–Organic Frameworks for Efficient Separation and Purification of Astaxanthin by Defect Engineering

Na,

Xing,

Tan

et al. 2024

Advanced Science

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Efficient separation of bioactive compounds from nature source, particularly that of astaxanthin (AXT), remains challenging due to their low content in complicated matrix and readily degradable structure. Herein, a modulator‐induced defect engineering is presented on the stable zirconium‐based metal–organic frameworks (Zr‐MOFs) to optimize pore size and pore chemistry for the efficient separation and purification of AXT for the first time. High adsorption capacity of 26.21 mg g−1 is achieved on the best‐performing defect Zr‐MOF (d‐UiO‐67‐4), superior over the other reported adsorbent for AXT. Meanwhile, d‐UiO‐67‐4 exhibits the selective adsorption of AXT over other carotenoids analogues with similar structure and properties. This is attributed to the preferential non‐covalent interactions between defect framework and AXT revealed by the spectroscopy analysis and density functional theory (DFT) calculations. High purity of AXT with 89.0% ± 2.3% extraction efficiency can be realized after the purification of AXT by d‐UiO‐67‐4. The practical separation performance of d‐UiO‐67‐4 for AXT extracted from Haematococcus pluvialis is demonstrated by fixed‐bed column‐based dynamic adsorption and desorption experiments. This work broadens the preparation methods for thermosensitive active substances and provided new research ideas for the controlled adsorption of functional food factors.

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Identifying UiO‐67 Metal‐Organic Framework Defects and Binding Sites through Ammonia Adsorption

Cited by 10 publications

References 95 publications

Molecular Structure, Dynamics, and Vibrational Spectroscopy of the Acetylene:Ammonia (1:1) Plastic Co-Crystal at Titan Conditions

Molecular Structure, Dynamics, and Vibrational Spectroscopy of the Acetylene:Ammonia (1:1) Plastic Co-Crystal at Titan Conditions

Anomalous Infrared Intensity Behavior of Acetonitrile Diffused into UiO-67

Fine‐Tuning Porous Structure of Zirconium‐Based Metal–Organic Frameworks for Efficient Separation and Purification of Astaxanthin by Defect Engineering

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