Nanosheets of a Layered Metal-Organic Framework for Separation of CO2/CH4 using Mixed Matrix Membranes.

Mixed matrix membranes represent an important technology for gas separations. Nanosheets of metal-organic framework (MOF) materials of high aspect ratio and size-selective gas transport properties have the potential to promote the efficient mixing of components to form membranes for gas separation. Herein, we report a bottom-up synthesis of extended sheets of kagomé (kgm) topology, kgmt-Bu, via the linkage of [Cu2(O2CR)4] paddlewheels with 5-tert-butylisophthalic acid. The growth of the layered structure can be controlled by the choice of solvent and modulator. Nanosheets of kgmt-Bu of average thickness of 20 nm and aspect ratio of 40 to 50 can be obtained, and the sieving effect of the channels in kgmt-Bu boost the efficient separation of CO2 over CH4. A mixed matrix membrane comprising kgmt-Bu nanosheets with Matrimid shows a 32% enhancement in CO2/CH4 selectivity compared with the membrane incorporating the MOF in the particulate form.

Optimizing Thermoelectric Properties through Compositional Engineering in Ag-Deficient AgSbTe2 Synthesized by Arc Melting.

Thermoelectric materials offer a promising avenue for energy management, directly converting heat into electrical energy. Among them, AgSbTe2 has gained significant attention and continues to be a subject of research at further improving its thermoelectric performance and expanding its practical applications. This study focuses on Ag-deficient Ag0.7Sb1.12Te2 and Ag0.7Sb1.12Te1.95Se0.05 materials, examining the impact of compositional engineering within the AgSbTe2 thermoelectric system. These materials have been rapidly synthesized using an arc-melting technique, resulting in the production of dense nanostructured pellets. Detailed analysis through scanning electron microscopy (SEM) reveals the presence of a layered nanostructure, which significantly influences the thermoelectric properties of these materials. Synchrotron X-ray diffraction reveals significant changes in the lattice parameters and atomic displacement parameters (ADPs) that suggest a weakening of bond order in the structure. The thermoelectric characterization highlights the enhanced power factor of Ag-deficient materials that, combined with the low glass-like thermal conductivity, results in a significant improvement in the figure of merit, achieving zT values of 1.25 in Ag0.7Sb1.12Te2 and 1.01 in Ag0.7Sb1.12Te1.95Se0.05 at 750 K.

Multiscale Length Structural Investigation and Thermoelectric Performance of Double-Filled Sr0.2Yb0.2Co4Sb12: An Exceptional Thermal Conductivity Reduction by Filler Segregation to the Grain Boundaries.

Among thermoelectric materials, skutterudites are the most prominent candidates in the mid-temperature range applications. In the multiple-filled Sr0.2Yb0.2Co4Sb12 skutterudite, with Sr and Yb as fillers, we have enhanced the thermoelectric performance of CoSb3 through the reduction of lattice thermal conductivity and the optimization of carrier concentration and electrical conductivity. The high-pressure synthesis of the double-filled derivative promotes filling fraction fluctuation. This is observed by high angular resolution synchrotron X-ray diffraction, showing a phase segregation that corresponds to an inhomogeneous distribution of the filler atoms, located at the 2a positions of the cubic space group Im3̅. In addition, scanning transmission electron microscopy (STEM) combined with EELS spectroscopy clearly shows a segregation of Sr atoms from the surface of the grains, which is compatible with the synchrotron X-ray powder diffraction results. Mean square displacement parameters analysis results in Einstein temperatures of ∼94 and ∼67 K for Sr and Yb, respectively, and a Debye temperature of ∼250 K. The strong effect on resonant and disorder scattering yields a significantly lower lattice thermal conductivity of 2.5 W m-1 K-1 at 773 K. Still, good weighed-mobility values were obtained, with high filling fraction of the Yb and Sr elements. This drives a reduced electrical resistivity of 2.1 × 10-5 Ω m, which leads to a peak zT of 0.26 at 773 K. The analysis and results performed for the synthesized (Sr,Yb)-double filled CoSb3, shed light on skutterudites for potential waste-heat recovery applications.

Non-Destructive and Non-Invasive Approaches for the Identification of Hydroxy Lead-Calcium Phosphate Solid Solutions ((PbxCa1-x)5(PO4)3OH) in Cultural Heritage Materials.

Lead-calcium phosphates are unusual compounds sometimes found in different kinds of cultural heritage objects. Structural and physicochemical properties of this family of materials, which fall into the hydroxypyromorphite-hydroxyapatite solid solution, or (PbxCa1-x)5(PO4)3OH, have received considerable attention during the last few decades for promising applications in different fields of environmental and material sciences, but their diagnostic implications in the cultural heritage context have been poorly explored. This paper aims to provide a clearer understanding of the relationship between compositional and structural properties of the peculiar series of (PbxCa1-x)5(PO4)3OH solid solutions and to determine key markers for their proper non-destructive and non-invasive identification in cultural heritage samples and objects. For this purpose, a systematic study of powders and paint mock-ups made up of commercial and in-house synthesized (PbxCa1-x)5(PO4)3OH compounds with a different Pb2+/Ca2+ ratio was carried out via a multi-technique approach based on scanning electron microscopy, synchrotron radiation-based X-ray techniques, i.e., X-ray powder diffraction and X-ray absorption near edge structure spectroscopy at the Ca K- and P K-edges, and vibrational spectroscopy methods, i.e., micro-Raman and Fourier transform infrared spectroscopy. The spectral modifications observed in the hydroxypyromorphite-hydroxyapatite solid solution series are discussed, by assessing the advantages and disadvantages of the proposed techniques and by providing reference data and optimized approaches for future non-destructive and non-invasive applications to study cultural heritage objects and samples.

Potassium-Promoted Limestone for Preferential Direct Hydrogenation of Carbonates in Integrated CO2 Capture and Utilization.

Integrated CO2 capture and utilization (ICCU) via the reverse water-gas shift (RWGS) reaction offers a particularly promising route for converting diluted CO2 into CO using renewable H2. Current ICCU-RWGS processes typically involve a gas-gas catalytic reaction whose efficiency is inherently limited by the Le Chatelier principle and side reactions. Here, we show a highly efficient ICCU process based on gas-solid carbonate hydrogenation using K promoted CaO (K-CaO) as a dual functional sorbent and catalyst. Importantly, this material allows ∼100% CO2 capture efficiency during carbonation and bypasses the thermodynamic limitations of conventional gas-phase catalytic processes in hydrogenation of ICCU, achieving >95% CO2-to-CO conversion with ∼100% selectivity. We showed that the excellent functionalities of the K-CaO materials arose from the formation of K2Ca(CO3)2 bicarbonates with septal K2CO3 and CaCO3 layers, which preferentially undergo a direct gas-solid phase carbonates hydrogenation leading to the formation of CO, K2CO3 CaO and H2O. This work highlights the immediate potential of K-CaO as a class of dual-functional material for highly efficient ICCU and provides a new rationale for designing functional materials that could benefit the real-life application of ICCU processes.

Hydrogen bonding patterns and C-H...π interactions in the structure of the antiparkinsonian drug (R)-rasagiline mesylate determined using laboratory and synchrotron X-ray powder diffraction data.

The structure of (R)-rasagiline mesylate [(R)-RasH+·Mes-], an active pharmaceutical ingredient used to treat Parkinson's disease, is presented. The structure was determined from laboratory and synchrotron powder diffraction data, refined using the Rietveld method, and validated and optimized using dispersion-corrected DFT calculations. The unit-cell parameters obtained in both experiments are in good agreement and the refinement with both datasets converged to good agreement factors. The final parameters obtained from laboratory data were a = 5.4905 (8), b = 6.536 (2), c = 38.953 (3) Å, V = 1398.0 (4) Å3 and from synchrotron powder data were a = 5.487530 (10) Å, b = 6.528939 (12) Å, c = 38.94313 (9) Å, V = 1395.245 (5) Å3 with Z = 4 and space group P212121. Preferred orientation was properly accounted for using the synchrotron radiation data, leading to a March-Dollase parameter of 1.140 (1) instead of the 0.642 (1) value obtained from laboratory data. In the structure, (R)-RasH+ moieties form layers parallel to the ab plane connected by mesylate ions through N-H...O and C-H...O hydrogen bonds. These layers stack along the c axis and are further connected by C-H...π interactions. Hirshfeld surface analysis and fingerprint plot calculations indicate that the main interactions are: H...H (50.9%), H...C/C...H (27.1%) and H...O/O...H (21.1%).

ID22 - the high-resolution powder-diffraction beamline at ESRF.

Following Phase 2 of the upgrade of the ESRF in which the storage ring was replaced by a new low-emittance ring along with many other facility upgrades, the status of ID22, the high-resolution powder-diffraction beamline, is described. The beamline has an in-vacuum undulator as source providing X-rays in the range 6-75 keV. ID22's principle characteristics include very high angular resolution as a result of the highly collimated and monochromatic beam, coupled with a 13-channel Si 111 multi-analyser stage between the sample and a Dectris Eiger2 X 2M-W CdTe pixel detector. The detector's axial resolution allows recorded 2θ values to be automatically corrected for the effects of axial divergence, resulting in narrower and more-symmetric peaks compared with the previous fixed-axial-slit arrangement. The axial acceptance can also be increased with increasing diffraction angle, thus simultaneously improving the statistical quality of high-angle data. A complementary Perkin Elmer XRD1611 medical-imaging detector is available for faster, lower-resolution data, often used at photon energies of 60-70 keV for pair-distribution function analysis, although this is also possible in high-resolution mode by scanning up to 120°â€…2θ at 35 keV. There are various sample environments, allowing sample temperatures from 4 K to 1600°C, a capillary cell for non-corrosive gas atmospheres in the range 0-100 bar, and a sample-changing robot that can accommodate 75 capillary samples compatible with the temperature range 80 K to 950°C.

EIGER2 hybrid-photon-counting X-ray detectors for advanced synchrotron diffraction experiments.

The ability to utilize a hybrid-photon-counting detector to its full potential can significantly influence data quality, data collection speed, as well as development of elaborate data acquisition schemes. This paper facilitates the optimal use of EIGER2 detectors by providing theory and practical advice on (i) the relation between detector design, technical specifications and operating modes, (ii) the use of corrections and calibrations, and (iii) new acquisition features: a double-gating mode, 8-bit readout mode for increasing temporal resolution, and lines region-of-interest readout mode for frame rates up to 98 kHz. Examples of the implementation and application of EIGER2 at several synchrotron sources (ESRF, PETRA III/DESY, ELETTRA, AS/ANSTO) are presented: high accuracy of high-throughput data in serial crystallography using hard X-rays; suppressing higher harmonics of undulator radiation, improving peak shapes, increasing data collection speed in powder X-ray diffraction; faster ptychography scans; and cleaner and faster pump-and-probe experiments.

Temperature-dependent rearrangement of gas molecules in ultramicroporous materials for tunable adsorption of CO2 and C2H2.

The interactions between adsorbed gas molecules within porous metal-organic frameworks are crucial to gas selectivity but remain poorly explored. Here, we report the modulation of packing geometries of CO2 and C2H2 clusters within the ultramicroporous CUK-1 material as a function of temperature. In-situ synchrotron X-ray diffraction reveals a unique temperature-dependent reversal of CO2 and C2H2 adsorption affinities on CUK-1, which is validated by gas sorption and dynamic breakthrough experiments, affording high-purity C2H2 (99.95%) from the equimolar mixture of C2H2/CO2 via a one-step purification process. At low temperatures (<253 K), CUK-1 preferentially adsorbs CO2 with both high selectivity (>10) and capacity (170 cm3 g-1) owing to the formation of CO2 tetramers that simultaneously maximize the guest-guest and host-guest interactions. At room temperature, conventionally selective adsorption of C2H2 is observed. The selectivity reversal, structural robustness, and facile regeneration of CUK-1 suggest its potential for producing high-purity C2H2 by temperature-swing sorption.

Illustrating papyrus in Ancient Egypt.

Illustrated papyruses from Ancient Egypt have survived across millennia, depicting with vivid colors numerous stories and practices from a distant past. We have investigated a series of illustrated papyruses from Champollion's private collection showing scenes from the Book of the Dead, a document essential to prepare for the afterlife. The nature of the different pigments and their distribution are revealed by combining optical microscopy, Raman spectroscopy, and synchrotron X-ray powder diffraction and fluorescence. The standardized three-step process from the New Kingdom period was used, comprising a preparatory drawing made of red hematite, a coloring step using pigments from the Egyptian palette, and a final black contour drawn with a carbon-based ink. Interestingly, specific pigment mixes were deliberately chosen to obtain different shades. In some parts, the final contour significantly differs from the preliminary drawing, revealing the artist's creativity. These results enhance our knowledge of illustrative practices in Ancient Egypt.

Effects of aluminum incorporation on the schwertmannite structure and surface properties.

Schwertmannite is a common nanomineral in acid sulfate environments such as Acid Mine Drainage (AMD) and Acid Sulfate Soils (ASS). Its high surface area and positively charged surface result in a strong affinity towards toxic oxyanions such as arsenate in solution. However, natural precipitation of schwertmannite also involves the accumulation of other impurities, in particular aluminum, an element that is often incorporated into the structure of Fe-oxide minerals, such as goethite and ferrihydrite, affecting their structural and surface properties. However, little is known about the effect of Al incorporation in schwertmannite on the removal capacity of toxic oxyanions found in AMD and ASS (e.g. arsenate). In this paper, schwertmannite samples with variable Al concentration were synthetized and employed in arsenate adsorption isotherm experiments at a constant pH of 3.5. Solid samples before and after arsenate adsorption were characterized using high energy X-ray diffraction and pair distribution function analyses in order to identify structural differences correlated with the Al content as well as variations in the coordination of arsenate adsorbed on the mineral surface. These analyses showed limited Al accumulation on schwertmannite (up to 5%) with a low effect on its structure. The maximum arsenate sorption capacity (258 mmolH2AsO4 molFe-1) was in the range of that with pure schwertmannite, but a higher proportion of inner-sphere coordination was observed. Finally, Al was found to desorb from schwertmannite, with adsorbed arsenate preventing this effect and increasing the stability of the mineral. These results are useful to interpret observations from the field, in particular from river water affected by AMD and ASS, where similar conditions are observed, and where aluminum incorporation is expected.

Tuning the Magnetization of Manganese (II) Carbonate by Intracrystalline Amino Acids.

Incorporation of organic molecules into the lattice of inorganic crystalline hosts is a common phenomenon in biomineralization and is shown to alter various properties of the crystalline host. Taking this phenomenon as a source of inspiration, it is shown herein that incorporation of specific single amino acids into the lattice of manganese (II) carbonate strongly alters its inherent magnetic properties. At room temperature, the magnetic susceptibility of the amino-acid-incorporating paramagnetic MnCO3 decreases, following a simple rule of mixtures. When cooled below the Néel temperature, however, the opposite trend is observed, namely an increase in magnetic susceptibility measured in a high magnetic field. Such an increase, accompanied by a drastic change in the Néel phase transformation temperature, results from a decrease in MnCO3 orbital overlapping and the weakening of superexchange interactions. It may be that this is the first time that the magnetic properties of a host crystal are tuned via the incorporation of amino acids.

Chemistry, Local Molybdenum Clustering, and Electrochemistry in the Li2+xMo1-xO3 Solid Solutions.

A broad range of cationic nonstoichiometry has been demonstrated for the Li-rich layered rock-salt-type oxide Li2MoO3, which has generally been considered as a phase with a well-defined chemical composition. Li2+xMo1-xO3 (-0.037 ≤ x ≤ 0.124) solid solutions were synthesized via hydrogen reduction of Li2MoO4 in the temperature range of 650-1100 °C, with x decreasing with the increase of the reduction temperature. The solid solutions adopt a monoclinically distorted O3-type layered average structure and demonstrate a robust local ordering of the Li cations and Mo3 triangular clusters within the mixed Li/Mo cationic layers. The local structure was scrutinized in detail by electron diffraction and aberration-corrected scanning transmission electron microcopy (STEM), resulting in an ordering model comprising a uniform distribution of the Mo3 clusters compatible with local electroneutrality and chemical composition. The geometry of the triangular clusters with their oxygen environment (Mo3O13 groups) has been directly visualized using differential phase contrast STEM imaging. The established local structure was used as input for density functional theory (DFT)-based calculations; they support the proposed atomic arrangement and provide a plausible explanation for the staircase galvanostatic charge profiles upon electrochemical Li+ extraction from Li2+xMo1-xO3 in Li cells. According to DFT, all electrochemical capacity in Li2+xMo1-xO3 solely originates from the cationic Mo redox process, which proceeds via oxidation of the Mo3 triangular clusters into bent Mo3 chains where the electronic capacity of the clusters depends on the initial chemical composition and Mo oxidation state defining the width of the first charge low-voltage plateau. Further oxidation at the high-voltage plateau proceeds through decomposition of the Mo3 chains into Mo2 dimers and further into individual Mo6+ cations.

High-Mg calcite nanoparticles within a low-Mg calcite matrix: A widespread phenomenon in biomineralization.

During the process of biomineralization, organisms utilize various biostrategies to enhance the mechanical durability of their skeletons. In this work, we establish that the presence of high-Mg nanoparticles embedded within lower-Mg calcite matrices is a widespread strategy utilized by various organisms from different kingdoms and phyla to improve the mechanical properties of their high-Mg calcite skeletons. We show that such phase separation and the formation of high-Mg nanoparticles are most probably achieved through spinodal decomposition of an amorphous Mg-calcite precursor. Such decomposition is independent of the biological characteristics of the studied organisms belonging to different phyla and even kingdoms but rather, originates from their similar chemical composition and a specific Mg content within their skeletons, which generally ranges from 14 to 48 mol % of Mg. We show evidence of high-Mg calcite nanoparticles in the cases of six biologically different organisms all demonstrating more than 14 mol % Mg-calcite and consider it likely that this phenomenon is immeasurably more prevalent in nature. We also establish the absence of these high-Mg nanoparticles in organisms whose Mg content is lower than 14 mol %, providing further evidence that whether or not spinodal decomposition of an amorphous Mg-calcite precursor takes place is determined by the amount of Mg it contains. The valuable knowledge gained from this biostrategy significantly impacts the understanding of how biominerals, although composed of intrinsically brittle materials, can effectively resist fracture. Moreover, our theoretical calculations clearly suggest that formation of Mg-rich nanoprecipitates greatly enhances the hardness of the biomineralized tissue as well.

The "Historical Materials BAG": A New Facilitated Access to Synchrotron X-ray Diffraction Analyses for Cultural Heritage Materials at the European Synchrotron Radiation Facility.

The European Synchrotron Radiation Facility (ESRF) has recently commissioned the new Extremely Brilliant Source (EBS). The gain in brightness as well as the continuous development of beamline instruments boosts the beamline performances, in particular in terms of accelerated data acquisition. This has motivated the development of new access modes as an alternative to standard proposals for access to beamtime, in particular via the "block allocation group" (BAG) mode. Here, we present the recently implemented "historical materials BAG": a community proposal giving to 10 European institutes the opportunity for guaranteed beamtime at two X-ray powder diffraction (XRPD) beamlines-ID13, for 2D high lateral resolution XRPD mapping, and ID22 for high angular resolution XRPD bulk analyses-with a particular focus on applications to cultural heritage. The capabilities offered by these instruments, the specific hardware and software developments to facilitate and speed-up data acquisition and data processing are detailed, and the first results from this new access are illustrated with recent applications to pigments, paintings, ceramics and wood.

Thermal Expansion and Rattling Behavior of Gd-Filled Co4Sb12 Skutterudite Determined by High-Resolution Synchrotron X-ray Diffraction.

In this work, Gd-filled skutterudite GdxCo4Sb12 was prepared using one step method under high pressure in a piston-cylinder-based press at 3.5 GPa and moderate temperature of 800 °C. A detailed structural characterization was performed using synchrotron X-ray diffraction (SXRD), revealing a filling fraction of x = 0.033(2) and an average bond length of 3.3499(3) Å. The lattice thermal expansion accessed via temperature-dependent SXRD led to a precise determination of a Debye temperature of 322(3) K, from the fitting of the unit-cell volume expansion using the second order Grüneisen approximation. This parameter, when evaluated through the mean square displacements of Co and Sb, displayed a value of 265(2) K, meaning that the application of the harmonic Debye theory underestimates the Debye temperature in skutterudites. Regarding the Gd atom, its intrinsic disorder value was ~5× and ~25× higher than those of the Co and Sb, respectively, denoting that Gd has a strong rattling behavior with an Einstein temperature of θE = 67(2) K. As a result, an ultra-low thermal conductivity of 0.89 W/m·K at 773 K was obtained, leading to a thermoelectric efficiency zT of 0.5 at 673 K.

Structure determination of riboflavin by synchrotron high-resolution powder X-ray diffraction.

The crystal structure of the stable form of vitamin B2 or riboflavin (C17H20N4O6) was solved using high-resolution powder X-ray diffraction (PXRD). The high-resolution PXRD pattern of riboflavin was recorded at room temperature at the European Synchrotron Radiation Facility (Grenoble, France). The starting structural model was generated using a Monte Carlo simulated annealing method. The final structure was obtained through Rietveld refinement. The positions of the H atoms belonging to hydroxy groups were estimated from computational energy minimizations. The symmetry is orthorhombic with the space group P212121 and the following lattice parameters: a = 20.01308, b = 15.07337 and c = 5.31565 Å.

Combining a multi-analyzer stage with a two-dimensional detector for high-resolution powder X-ray diffraction: correcting the angular scale.

In a test experiment, a two-dimensional pixel detector was mounted on the nine-channel multi-analyzer stage of the high-resolution powder diffraction beamline ID22 at the ESRF. This detector replaces a bank of scintillation counters that detect the diffracted intensity passing via the analyzer crystals as the diffractometer arm is scanned. At each diffractometer detector arm angle 2Θ, a 2D image is recorded that displays nine distinct regions of interest corresponding to the diffraction signals transmitted by each of the analyzer crystals. Summing pixels from within each region of interest allows the diffracted intensity to be extracted for each channel. X-rays are diffracted from the sample at various angles, 2θ, into Debye-Scherrer cones. Depending on the azimuthal angle around the cone, diffracted photons satisfy the analyzer-crystal Bragg condition at different diffractometer 2Θ values and arrive on the detector at different horizontal (axial) positions. The more the azimuthal angle deviates from diffraction in the vertical plane, the lower the 2Θ angle at which it is transmitted by an analyzer crystal, and the greater the distance of the detecting pixel from the centerline of the detector. This paper illustrates how the axial resolution afforded by the pixel detector can be used to correct the apparent diffraction angle, 2Θ, given by the diffractometer arm to its true diffraction angle, 2θ. This allows a reduction in peak asymmetry at low angle, and even with a relatively small axial acceptance, the correction leads to narrower peaks than if no correction is applied. By varying axial acceptance with diffraction angle, it is possible to optimize angular resolution at low diffraction angles and counting statistics at high angles. In addition, there is an intrinsic peak broadening with increasing azimuthal angle, dependent on the axial beam and detector pixel sizes. This effect reduces with 2θ, as the curvature of the Debye-Scherrer cones decreases. This broadening can be estimated and used to help choose the axial range to include as a function of diffraction angle.

Revealing the Nature of Black Pigments Used on Ancient Egyptian Papyri from Champollion Collection.

Although numerous papyri from ancient Egypt have been collected and preserved over the centuries, the recipe used to prepare black inks was only reported in manuscripts from the late Greco-Roman period. Black inks were mostly obtained after mixing carbon black with a binder agent and water. In previous studies performed on black inks apposed on papyri from ancient Egypt, additional chemical elements such as lead, iron, or copper were also identified, and the resulting chemical contrast with the papyrus support was used to virtually decrypt highly degraded or rolled papyri. Combining a series of synchrotron-based techniques with Raman spectroscopy and scanning electron microscopy, we investigated 10 papyri fragments from J.-F. Champollion's private collection. For each fragment, the carbon-black pigment found in the ink is identified as flame carbon (lampblack or soot). Using X-ray diffraction computed tomography, we show that the diffraction signal of the carbon-based pigment itself can be isolated. As a result, a contrast with the papyrus support is obtained, even in the absence of a specific chemical element in the ink. This is opening up new opportunities to decipher words written millennia ago, as part of our Cultural Heritage.

Adsorption of Nitrogen Dioxide in a Redox-Active Vanadium Metal-Organic Framework Material.

Nitrogen dioxide (NO2) is a toxic air pollutant, and efficient abatement technologies are important to mitigate the many associated health and environmental problems. Here, we report the reactive adsorption of NO2 in a redox-active metal-organic framework (MOF), MFM-300(V). Adsorption of NO2 induces the oxidation of V(III) to V(IV) centers in MFM-300(V), and this is accompanied by the reduction of adsorbed NO2 to NO and the release of water via deprotonation of the framework hydroxyl groups, as confirmed by synchrotron X-ray diffraction and various experimental techniques. The efficient packing of {NO2·N2O4}∞ chains in the pores of MFM-300(VIV) results in a high isothermal NO2 uptake of 13.0 mmol g-1 at 298 K and 1.0 bar and is retained for multiple adsorption-desorption cycles. This work will inspire the design of redox-active sorbents that exhibit reductive adsorption of NO2 for the elimination of air pollutants.