X-ray Pair Distribution Function Research Articles

On “Reexamination of the structure of opal-A: A combined study of synchrotron X-ray diffraction and pair distribution function analysis”—Reply to de Jong

On “Reexamination of the structure of opal-A: A combined study of synchrotron X-ray diffraction and pair distribution function analysis”—Reply to de Jong

Comment on “Reexamination of the structure of opal-A: A combined study of synchrotron X-ray diffraction and pair distribution function analysis”—Concerning opal

Comment on “Reexamination of the structure of opal-A: A combined study of synchrotron X-ray diffraction and pair distribution function analysis”—Concerning opal

Recycling of Aluminosilicate-Based Solid Wastes through Alkali-Activation: Preparation, Characterization, and Challenges

Recycling aluminosilicate-based solid wastes is imperative to realize the sustainable development of constructions. By using alkali activation technology, aluminosilicate-based solid wastes, such as furnace slag, fly ash, red mud, and most of the bio-ashes, can be turned into alternative binder materials to Portland cement to reduce the carbon footprint of the construction and maintenance activities of concrete structures. In this paper, the chemistry involved in the formation of alkali-activated materials (AAMs) and the influential factors of their properties are briefly reviewed. The commonly used methods, including X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TG), nuclear magnetic resonance spectroscopy (NMR), and X-ray pair distribution function technology, to characterize the microstructure of AAMs are introduced. Typical characterization results of AAMs are shown and the limitations of each method are discussed. The main challenges, such as shrinkage, creep, efflorescence, carbonation, alkali–silica reaction, and chloride ingress, to conquer for a wider application of AAMs are reviewed. It is shown that several performances of AAMs under certain circumstances seem to be less satisfactory than traditional portland cement systems. Existing strategies to improve these performances are reviewed, and recommendations for future studies are given.

MLstructureMining: a machine learning tool for structure identification from X-ray pair distribution functions

We present MLstructureMining, a machine learning tool that identifies a structural model from an experimental pair distribution function. We show how the method can be used for structure analysis of both crystalline and nanocrystalline materials.

Molecular structure of ketoprofen-polyvinylpyrrolidone solid dispersions prepared by different amorphization methods.

Amorphous solid dispersions (ASDs) are a widely studied formulation approach for improving the bioavailability of poorly water-soluble pharmaceuticals. Yet, a complete understanding remains lacking for how specific processing methods may influence ASDs' molecular structure. We prepare ketoprofen/polyvinylpyrrolidone (KTP/PVP) ASDs, ranging from 0-75 wt% KTP, using five different amorphization techniques: melt quenching, rotary evaporation with vacuum drying, spray drying, and acoustic levitation with either a premixed solution or in situ mixing of separate co-sprayed solutions. The co-spray levitation approach enables on-demand compositional changes in a containerless processing environment, while requiring minimal pharmaceutical material (∼1 mg). The structure of all ASDs are then compared using high-energy X-ray total scattering. X-ray pair distribution functions are similar for most ASDs of a given composition (Rx = 0.4-2.5%), which is consistent with them having similar intramolecular structure. More notably, differences in the X-ray structure factors for the various amorphization routes indicate differing extents of molecular mixing, a direct indication of their relative stability against crystallization. Melt quenching, spray drying, and levitation of premixed solutions exhibit some degree of molecular mixing, while the co-sprayed levitation samples have molecular arrangements like those of KTP/PVP physical mixtures. These findings illustrate how X-ray total scattering can be used to benchmark amorphous forms prepared by different techniques.

Copper single-site engineering in MOF-808 membranes for improved water treatment.

MOF-808, a metal-organic framework containing Zr6O8 clusters, can serve as a secure anchoring point for stabilizing copper single-sites with redox activity, thus making it a promising candidate for catalytic applications. In this study, we target the incorporation of Cu-MOF-808 into a mixed-matrix membrane for the degradation of tyrosol, an emerging endocrine-disrupting compound commonly found in water sources, through Fenton reactions, developing innovative technologies for water treatment. We successfully demonstrate the effectiveness of this approach by preparing catalytic membranes with minimal metal leaching, which is one of the primary challenges in developing copper-based Fenton heterogeneous catalysts. Furthermore, we utilized advanced synchrotron characterization techniques, combining X-ray absorption spectroscopy and pair distribution function analysis of X-ray total scattering, to provide evidence of the atomic structure of the catalytic copper sites within the membranes. Additionally, we observed the presence of weak interactions between the MOF-808 and the organic polymer, potentially explaining their enhanced stability.

Resilience of the Aurivillius structure upon La and Cr doping in a Bi5Ti3FeO15 multiferroic.

Combining the experimental techniques of high-resolution X-ray diffraction, magnetometry, specific heat measurement, and X-ray photoelectron, Raman and dielectric spectroscopy techniques, we have studied the influence of La and Cr doping on the crystal structure and magnetism of the room temperature Aurivillius multiferroic Bi5Ti3FeO15 by investigating the physical properties of (Bi4La)Ti3FeO15 and Bi5Ti3 (Fe0.5Cr0.5)O15. The parent (Bi5Ti3FeO15) and the doped ((Bi4La)Ti3FeO15 and Bi5Ti3(Fe0.5Cr0.5)O15) compounds crystallize in the A21am space group, which is confirmed through our analysis of high-resolution synchrotron X-ray diffraction data obtained on phase-pure polycrystalline powders. We determined the oxidation states of the metal atoms in the studied compounds as Fe3+, Ti4+, Cr3+, and La3+ through the analysis of X-ray photoelectron spectroscopy data. The magnetic susceptibilities of the three compounds are marked by the absence of a long-range ordered ground state, but dominated by superparamagnetic clusters with dominant antiferromagnetic interactions. This signature of short-range magnetism is also seen in specific heat as a low temperature enhancement which is suppressed upon the application of external magnetic fields up to 8 T. Our dielectric spectroscopy experiments showed that the three studied compounds display similar features in the dielectric constant measured as a function of frequency. However, upon doping La at the Bi site, the width of the ferroelectric hysteresis loop increases for (Bi4La)Ti3FeO15 compared to that of the parent compound Bi5Ti3FeO15, and with Cr doping, Bi5Ti3(Fe0.5Cr0.5)O15 becomes a leaky dielectric. The resilience of the Aurivillius crystal structure towards doping of La at the Bi site and Cr at the Fe site is clearly seen in the bulk properties of magnetic susceptibility, specific heat and the average crystal structure. The relevance of changes in the local structure is evident from our Raman spectroscopy and X-ray pair distribution function studies.

Revealing the Cycling and Degradation Mechanism of Bi-Metallates As Anode Materials for Na-Ion Batteries

Na-ion batteries (NIBs) represent an emerging alternative to modern Li-ion batteries. To improve the overall performance of NIBs it is crucial to develop new types of anode materials with high capacity and long cycle life. Among the anode candidates, materials operating under combined conversion and alloying mechanisms (CAMs) are considered as promising. They are capable of delivering high capacity, however, despite theoretical predictions the cycling stability is still below expectations. Therefore, a comprehensive understanding of the cycling and degradation mechanisms of CAMs is crucial to improve their performance. However, these materials undergo multiple chemical transformations, which often involves formation of amorphous and nanocrystalline phases during cycling. Such chemical complexity substantially impedes their full characterization and understanding.Bismuth metallates, with a general formula of Bi-TM-O (TM = transition metal), is a group of ternary CAMs. Their general cycling mechanism consists of an irreversible conversion reaction, which leads to formation of Bi nanoparticles embedded in a Na-TM-O matrix during the first sodiation. This is followed by a reversible two-step alloying reaction leading to formation of Na3Bi with NaBi as an intermediate phase. In this work, we have used operando X-ray diffraction over the course of ∼30 cycles to study the cycling and degradation mechanisms of two CAMs - Bi2MoO6 and BiFeO3. With the help of ex situ X-ray absorption spectroscopy and pair distribution function (PDF) analysis, we have revealed new insights into these materials in addition to confirming the general cycling mechanism.Both materials form the cubic phase of Na3Bi (c-Na3Bi) in the sodiated state with some noticeable differences. While, the hexagonal Na3Bi (h-Na3Bi) phase starts to form after 10 cycles in Bi2MoO6, a combination of c-Na3Bi and h-Na3Bi can be observed after the first cycle in BiFeO3. The formation of c-Na3Bi is kinetically favorable in these systems, while h-Na3Bi is the more thermodynamically stable and, therefore, forms later in the cycling process. Both materials shows three distinct regions of capacity degradation, where the first is initiated by a growth in the crystallite sizes of Bi-particles. This is followed by a disappearance of the Bi-phase as the second step. The last degradation phase is related to the disappearance of the NaBi-phase and locking the system in the sodiated state. The present talk will discuss the mechanisms of these degradation steps in view of the future development of CAMs in greater details. Figure 1

Crystallization of polarons through charge and spin ordering transitions in 1T-TaS2

The interaction of electrons with the lattice in metals can lead to reduction of their kinetic energy to the point where they may form heavy, dressed quasiparticles—polarons. Unfortunately, polaronic lattice distortions are difficult to distinguish from more conventional charge- and spin-ordering phenomena at low temperatures. Here we present a study of local symmetry breaking of the lattice structure on the picosecond timescale in the prototype layered dichalcogenide Mott insulator 1T-TaS2 using X-ray pair-distribution function measurements. We clearly identify symmetry-breaking polaronic lattice distortions at temperatures well above the ordered phases, and record the evolution of broken symmetry states from 915 K to 15 K. The data imply that charge ordering is driven by polaron crystallization into a Wigner crystal-like state, rather than Fermi surface nesting or conventional electron-phonon coupling. At intermediate temperatures the local lattice distortions are found to be consistent with a quantum spin liquid state.

Emergence of liquid following laser melting of gold thin films.

X-ray structural science is undergoing a revolution driven by the emergence of X-ray Free-electron Laser (XFEL) facilities. The structures of crystalline solids can now be studied on the picosecond time scale relevant to phonons, atomic vibrations which travel at acoustic velocities. In the work presented here, X-ray diffuse scattering is employed to characterize the time dependence of the liquid phase emerging from femtosecond laser-induced melting of polycrystalline gold thin films using an XFEL. In a previous analysis of Bragg peak profiles, we showed the supersonic disappearance of the solid phase and presented a model of pumped hot electrons carrying energy from the gold surface to scatter at internal grain boundaries. This generates melt fronts propagating relatively slowly into the crystal grains. By conversion of diffuse scattering to a partial X-ray pair distribution function, we demonstrate that it has the characteristic shape obtained by Fourier transformation of the measured F(Q). The diffuse signal fraction increases with a characteristic rise-time of 13 ps, roughly independent of the incident pump fluence and consequent final liquid fraction. This suggests the role of further melt-front nucleation processes beyond grain boundaries.

Atomic-scale structure of RCo2 (R[dbnd]Tb,Dy) compounds studied by X-ray diffraction and pair distribution function analysis

The RCo2 compounds have attracted lots of research interests due to the giant magnetostriction effect. The average structure of these compounds have been well established, but the studies on the local structure are still rare. In this paper, the average structure and the local structure of the RCo2 (RTb, Dy) compounds were investigated with a combination of X-ray diffraction (XRD) and pair distribution function (PDF) analysis, and the electronic structure were studied by the first principle calculations. The results demonstrate that these two compounds present MgCu2-type cubic structure at both average and local scale at room temperature. The variation of the R–Co bond length is much larger than that of the Co–Co bond length with changing R element. The Co–Co bond of TbCo2 compound shows abnormal change around the structural transition. The hybridization between R-5d state and Co-3d state strongly affect the R–Co bond, while the magnetic polarization of Co-3d state show stronger effect on the Co–Co bond. These findings highlight the important role of atomic-scale structure in determining the magnetic properties of the RCo2 materials.

Probing Molecular Packing of Amorphous Pharmaceutical Solids Using X-ray Atomic Pair Distribution Function and Solid-State NMR.

The structural investigation of amorphous pharmaceuticals is of paramount importance in comprehending their physicochemical stability. However, it has remained a relatively underexplored realm primarily due to the limited availability of high-resolution analytical tools. In this study, we utilized the combined power of X-ray pair distribution functions (PDFs) and solid-state nuclear magnetic resonance (ssNMR) techniques to probe the molecular packing of amorphous posaconazole and its amorphous solid dispersion at the molecular level. Leveraging synchrotron X-ray PDF data and employing the empirical potential structure refinement (EPSR) methodology, we unraveled the existence of a rigid conformation and discerned short-range intermolecular C-F contacts within amorphous posaconazole. Encouragingly, our ssNMR 19F-13C distance measurements offered corroborative evidence supporting these findings. Furthermore, employing principal component analysis on the X-ray PDF and ssNMR data sets enabled us to gain invaluable insights into the chemical nature of the intermolecular interactions governing the drug-polymer interplay. These outcomes not only furnish crucial structural insights facilitating the comprehension of the underlying mechanisms governing the physicochemical stability but also underscore the efficacy of synergistically harnessing X-ray PDF and ssNMR techniques, complemented by robust modeling strategies, to achieve a high-resolution exploration of amorphous structures.

Molecular interactions in short-chain perfluoroalkyl carboxylic acids and aqueous solutions.

The presence of short-chain per- and polyfluoroalkyl substances in water poses a major health and environmental challenge. Here, we have performed high-energy small- and wide-angle X-ray scattering measurements on CF3[CF2]nCOOH (where n = 1, 2, 3 represents the chain length) and their aqueous solutions at 10% mole concentrations to characterize their molecular interactions at the atomic and nanometer length scales. The experimental wide-angle structure factors have been modelled using Empirical Potential Structural Refinement. The oxygen-oxygen partial X-ray pair distribution functions show that the coordination number between the hydroxyl oxygen on the acid and surrounding oxygen water molecules increases significantly with acid chain length, rising from 3.2 for n = 1 to 4.1 for n = 3. The small-angle scattering is dominated by a sharp, high-intensity peak at Q1 ∼ 0.2 Å-1 and a smaller peak at Q2 = 1.2 Å-1 for n = 3, both of which decrease with decreasing chain length. The Q2 peak is attributed to groups of adjacent non-bonded acid molecules, and Q1 has contributions from both correlations between acid molecules and water-water interactions. In all cases, the models show nanoscale aggregation occurs in the form of denser channels of winding hydrogen-bonded chains, approximately 20 water molecules in length, surrounding clusters of acid molecules. This article is part of the theme issue 'Exploring the length scales, timescales and chemistry of challenging materials (Part 2)'.

Discovery of New Fast Oxygen Conductors: Bi2MO4x (M= rare earth, X= halogen) Via Unsupervised Machine Learning

Discovering new fast oxygen conductors is critical for developing many technologies, e.g., solid oxide fuel cells (SOFCs), solid oxide electrolysis cells (SOECs), proton ceramic fuel cells (PCFCs), and solid oxide air batteries, particularly for operation at lower temperatures (below 700 ˚C). By leveraging unsupervised machine learning techniques and large databases of computed materials data (e.g., Materials Project), we are able to rapidly explore and screen for new materials with high oxygen mobility. In this work, we used unsupervised machine learning analysis applied to features extracted from the structure of materials and discovered a new structural class of vacancy-mediated oxygen conductor. To do this, we applied the K-nearest neighbor (k-NN) algorithm on all the approximately 62,000 oxygen-containing compounds in the Materials Project database, using X-ray diffraction (XRD) and pair distribution function (PDF) data to represent the structural features. The neighbors of reference known for good oxygen conductors were screened with criteria relating to material stability, synthesizability, and electronic property dissimilarity (to ensure a novel material) compared to the reference material. Starting with the best-known oxygen conductor, the fluorite-type material, we examined the materials list of its nearest neighbors and identified the Bi2MO4X (M=Rare-earth element, X= halogen element) structural family as a novel group of fast oxygen conductors. In particular, Bi2LaO4Cl is a layered bismuth oxyhalide crystallized in the space group P4/mmm, adopting a “triple fluorite” layer [Bi2LaO4]+, balanced by the anion Cl- layer. The stability and mobility of oxygen vacancy in Bi2LaO4Cl were studied using Density Functional Theory (DFT) methods. 2+ oxygen vacancy is the most thermodynamically favorable defect type. Ab initio and machine learning-trained interatomic potential molecular dynamic simulations were performed to study the high temperature oxygen mobility in Bi2LaO4Cl. The simulation results show that Bi2LaO4Cl presents an extremely low migration barrier of 0.14 +/- 0.03 eV below 700 ˚C, suggesting 10 to 20 times higher ionic conductivity compared to yttria-stabilized zirconia (YSZ). Bi2LaO4Cl is an insulator with a wide band gap of 2.65 eV, indicating that Bi2LaO4Cl may be a promising electrolyte material with high oxygen ion conductivity and low electronic conductivity. This work demonstrates the power of combining unsupervised machine learning approaches with large materials databases for finding new fast oxygen conductors.

A Negative-Based TiO2 Electrode for Aqueous Proton Batteries

Complementary solutions to Li-ion batteries must be studied for the growing need for energy demand. Accordingly, we have been interested in developing negative electrode materials of TiO2 capable of reversibly intercalating proton ions for aqueous batteries. One of these batteries’ main challenges comes from the low potential window available. Aqueous batteries cannot provide sufficient energy density with a thermodynamic working potential of only 1.23V. To do so, we have optimized the intrinsic transport properties of proton-ions can lead to the reduction of side reactions such as Hydrogen Evolution Reaction (HER).Solvothermal route synthesis made at different temperatures (from 90°C to 150°C) gives access to different TiO2 structures. At 90°C, a lamellar type lepidocrocite is obtained, including sheets of “TiO2” and water in the inter-lamellar spaces. This inter-lamellar space allows proton conduction by the Grotthus mechanism [1]. But, lepidocrocite type TiO2has been shown to be a non-conductive ionic conductor. To make it conductive, different cations can be inserted into the inter-lamellar space during the solvothermal synthesis, thus allowing the reorganization of water molecules, then facilitating the intercalation, conduction, and diffusion of protons [2]. Several levels of Zn2+ were tested: from 10 to 50 mol% relative to Ti4 +. At 150°C, we have been able to stabilize a complete condensed anatase (one polymorph of TiO2) phase while a defect anatase phase has been synthesized at a temperature between 90°C and 150°C. Interestingly, the quantity of defect can be tuned by the temperature and the hydrolysis ratio, h=nH2O/nTi=3.33 [3]. These defects are mainly cationic vacancies, thanks to X-Ray Pair Distribution Function (PDF) analysis.The electrochemical properties of these materials (shaped with carbon black as conductive support and Nafion as a binder) were studied in half-cell aqueous electrolyte buffered at pH 5 (CH3COOH/CH3COOK, pKa = 4.76, (1M)). Experimental capacities of more than 100 mAh/g, 80% of coulombic efficiency over 100 cycles have been obtained and potentials down to -1.4V (V vs Ag/AgCl, KCl saturated) have been achieved.For defective anatase (synthesized at 110°C), the CV curves exhibit two distinct peaks that can be linked to the co-existence of two sites for proton intercalation. The proton can be intercalated either inside a vacancy or within the lattice. This behavior allows a promising working potential of -1.6V with a gravimetric capacity of 250 mAh.g-1 with a 90% of efficiency over 50 cycles. Finally, the relationship between structure and electrochemical properties will be discussed in this presentation with the objective of designing an efficient MnO2/TiO2 aqueous battery.REFERENCE:[1] Wu, X.; Hong, J. J.; Shin, W.; Ma, L.; Liu, T.; Bi, X.; Yuan, Y.; Qi, Y.; Surta, T. W.; Huang, W.; Neuefeind, J.; Wu, T.; Greaney, P. A.; Lu, J.; Ji, X. Nat. Energy 2019, 4 (2), 123–130 [2] Chimie, E. D.; Analytique, C.; Centre, D. P.; Kang, P. S. Sorbonne Université Design de Matériaux Lamellaires Par Chimie Douce Pour Batteries à Proton et Ion Multivalent. 2020.[3] Kang, S; Singh. A; Badot, J-c; Reeves, K; Durand-Vidal, Serge, Legein, C; Body, Monique, Dubrunfaut, O; Borkiewez, O; Tremblay, B; Laberty-Robert, C; Dambournet, D Chemistry of Materials 2020 32 (21), 9458-9469 Figure 1

Structure and Ionic Conductivity of Li-Disordered Bismuth o-Thiophosphate Li60-3xBi16+x(PS4)36.

The structure of the first lithium-containing bismuth ortho (o)-thiophosphate was determined using a combination of powder X-ray, neutron, and electron diffraction. Li60-3xBi16+x(PS4)36 with x in the range of 4.1-6.5 possesses a complex monoclinic structure [space group C2/c (No. 15)] and a large unit cell with the lattice parameters a = 15.4866 Å, b = 10.3232 Å, c = 33.8046 Å, and β = 85.395° for Li44.4Bi21.2(PS4)36, in agreement with the structure as observed by X-ray and neutron pair distribution function analysis. The disordered distribution of lithium ions within the interstices of the dense host structure and the Li ion dynamics and diffusion pathways have been investigated by solid-state nuclear magnetic resonance (NMR) spectroscopy, pulsed field gradient NMR diffusion measurements, and bond valence sum calculations. The total lithium ion conductivities range from 2.6 × 10-7 to 2.8 × 10-6 S cm-1 at 20 °C with activation energies between 0.29 and 0.32 eV, depending on the bismuth content. Despite the highly disordered nature of lithium ions in Li60-3xBi16+x(PS4)36, the underlying dense host framework appears to limit the dimensionality of the lithium diffusion pathways and emphasizes once more the necessity of a close inspection of the structure-property relationships in solid electrolytes.

Exploring the impact of incoherent Compton scattering on X-ray pair distribution function analysis of disordered materials

X-ray atomic pair distribution function (XPDF) measurements using a two-dimensional area detector have been of great value in studying atomic structures of materials with varying degrees of disorder. However, an area detector does not have energy resolution. Thus, incoherent inelastic Compton scattering and fluorescence are not discriminated, contaminating coherent elastic scattering. This paper investigates the effects of random noise from incoherent scattering on XPDF analysis. To conduct the study, the elastic scattering, Compton scattering and fluorescence of In0.33Ga0.67As alloy were separately measured using an intrinsic Ge solid-state detector with energy resolution. It is found that the addition of Compton scattering with a noise-to-signal ratio of about 0.8% results in the smearing of diffuse scattering in the high-Q region. Moreover, adding extra noise from fluorescence increases the smearing, overwhelming the diffuse scattering. Additionally, simulated data of elastic and Compton scattering on ferroelectric Ba(Ti0.8Zr0.2)O3 were used to investigate the evolution of noise fluctuation and its effects on the XPDF as a function of total intensity.

Phosphate-functionalized Zirconium Metal-Organic Frameworks for Enhancing Lithium-Sulfur Battery Cycling.

Lithium-sulfur batteries are promising candidates for next-generation energy storage devices due to their outstanding theoretical energy density. However, they suffer from low sulfur utilization and poor cyclability, greatly limiting their practical implementation. Herein, we adopted a phosphate-functionalized zirconium metal-organic framework (Zr-MOF) as a sulfur host. With their porous structure, remarkable electrochemical stability, and synthetic versatility, Zr-MOFs present great potential in preventing soluble polysulfides from leaching. Phosphate groups were introduced to the framework post-synthetically since they have shown a strong affinity towards lithium polysulfides and an ability to facilitate Li ion transport. The successful incorporation of phosphate in MOF-808 was demonstrated by a series of techniques including infrared spectroscopy, solid-state nuclear magnetic resonance spectroscopy, and X-ray pair distribution function analysis. When employed in batteries, phosphate-functionalized Zr-MOF (MOF-808-PO4) exhibits significantly enhanced sulfur utilization and ion diffusion compared to the parent framework, leading to higher capacity and rate capability. The improved capacity retention and inhibited self-discharge rate also demonstrate effective polysulfide encapsulation utilizing MOF-808-PO4. Furthermore, we explored their potential towards high-density batteries by examining the cycling performance at various sulfur loadings. Our approach to correlate structure with function using hybrid inorganic-organic materials offers new chemical design strategies for advancing battery materials.

Mapping nanocrystalline disorder within an amorphous metal–organic framework

Intentionally disordered metal–organic frameworks (MOFs) display rich functional behaviour. However, the characterisation of their atomic structures remains incredibly challenging. X-ray pair distribution function techniques have been pivotal in determining their average local structure but are largely insensitive to spatial variations in the structure. Fe-BTC (BTC = 1,3,5-benzenetricarboxylate) is a nanocomposite MOF, known for its catalytic properties, comprising crystalline nanoparticles and an amorphous matrix. Here, we use scanning electron diffraction to first map the crystalline and amorphous components to evaluate domain size and then to carry out electron pair distribution function analysis to probe the spatially separated atomic structure of the amorphous matrix. Further Bragg scattering analysis reveals systematic orientational disorder within Fe-BTC’s nanocrystallites, showing over 10° of continuous lattice rotation across single particles. Finally, we identify candidate unit cells for the crystalline component. These independent structural analyses quantify disorder in Fe-BTC at the critical length scale for engineering composite MOF materials.

Direct Synthesis of Ammonia from Nitrate on Amorphous Graphene with Near 100% Efficiency.

Ammonia is an indispensable commodity in the agricultural and pharmaceutical industries. Direct nitrate-to-ammonia electroreduction is a decentralized route yet challenged by competing side reactions. Most catalysts are metal-based, and metal-free catalysts with high nitrate-to-ammonia conversion activity are rarely reported. Herein, it is shown that amorphous graphene synthesized by laser induction and comprising strained and disordered pentagons, hexagons, and heptagons can electrocatalyze the eight-electron reduction of NO3 - to NH3 with a Faradaic efficiency of ≈100% and an ammonia production rate of 2859 µg cm-2 h-1 at -0.93 V versus reversible hydrogen electrode. X-ray pair-distribution function analysis and electron microscopy reveal the unique molecular features of amorphous graphene that facilitate NO3 - reduction. In situ Fouriertransform infrared spectroscopy and theoretical calculations establish the critical role of these features in stabilizing thereaction intermediates via structural relaxation. The enhanced catalytic activity enables the implementation of flow electrolysis for the on-demand synthesis and release of ammonia with >70% selectivity, resulting in significantly increased yields and survival rates when applied to plant cultivation. The results of this study show significant promise for remediating nitrate-polluted water and completing the NOx cycle.