We investigate the pyrolysis of a polymer-derived porous SiCO gel through thermogravimetric analysis. Despite using “ultra-pure” (99.999

Electrochemical carbon monoxide reduction (COR) is a promising route for sustainable production of multicarbon chemicals from CO2, as it bypasses the large carbon losses of direct CO2 electroreduction. In most electrocatalysts currently explored to tune COR selectivity towards highadded value multicarbon oxygenated molecules, like acetate and ethanol, copper is the catalytic site of C-C bond formation. Herein, we show that by designing nanoparticles of a strongly covalent copper compound, CuSi2P3, we retain isolated copper atoms during COR and trigger the intervention of phosphorus atoms as C-C coupling sites, without directly involving copper atoms. This profound change in COR mechanism results in a high selectivity towards C2 molecules (80 % Faradaic efficiency), especially oxygenates (73%), at a current density of -150 mA cm-2. This work reveals the importance of tailoring, via the crystal structure, the local environment of metal atoms, to achieve original selectivity in COR with new families of electrocatalysts.

The importance of (bi)carbonate salts cannot be understated. They are vital to the Earth's geology and ecosystems and are used as precursors by chemists for the synthesis of functional materials. Naturally, solid-state NMR (ssNMR) appears as the spectroscopic tool of choice to probe the atomic-level structure and dynamics of (bi)carbonate salts. Of the possible nuclei available as spectroscopic probes in carbonate and bicarbonate ions (i.e., 1H, 13C, and 17O), oxygen-17 is highly attractive. Yet, it is seldom employed, largely due to its low natural abundance (0.04 %) and lack of practical enrichment protocols. Recently, we reported an effective 17O-labeling strategy involving mechanochemistry of Na2CO3·H2O, Na2CO3, NaHCO3, K2CO3·1.5H2O, and KHCO3, and recorded their 17O NMR spectral fingerprints near room temperature. In this work, ultra-low temperature (i.e., 100 K) 17O ssNMR spectra of these phases are acquired at two magnetic fields, 14.1 and 18.8 T, to extract the 17O NMR parameters δiso, CQ, and ηQ for the different oxygen sites, and to further study the influence of dynamics on the spectra. We compare the experimental 17O NMR parameters to those computed with GIPAW-DFT calculations both on static models, and after averaging by molecular dynamics (MD) simulations. This approach was taken to aid in analyzing the structure-spectra relationships and shed light on the dynamics. Lastly, we report the static GIPAW-DFT calculations of 17O NMR parameters for a series of other carbonate salts of interest, further expanding upon current experimental 17O ssNMR results.

NaSICON-type materials, such as Li1.3Al0.3Ti1.7(PO4)3 (LATP), are considered promising solid electrolytes due to their good total ionic conductivity of 1 x 10-4 S cm-1 at room temperature and their stability at high potentials (4.1 V vs Li/Li+). However, decreasing their densification temperature is crucial for their integration into all-solid-state batteries (ASSBs). The minimum required heat treatment temperature for densification of LATP is 900 degrees C, which is incompatible with its integration in the composite electrode of ASSBs due to reactivity with the positive electrode material (cathode). To lower this temperature, lithium salts are often proposed as sintering aids to promote liquid-phase sintering. However, the systematic formation of impurities, such as LiTiOPO4 and Li4P2O7, suggests that chemical reactivity plays a significant role in LATP densification. In this work, the chemical reactivity mechanism of lithium salts with LATP during densification and sintering was investigated. Various characterization techniques, including in situ and ex situ X-ray diffraction, TGA-DTA-MS, DSC, ex situ Raman and solid-state NMR spectroscopy (7Li, 27Al, and 31P), were employed to elucidate the mechanism. The formation of intermediate decomposition products Li3PO4 and TiO2 is identified for the first time via the reactivity of the lithium salt with LATP prior to the melting temperature of the salt. These intermediates subsequently react with LATP at a higher temperature, resulting in the formation of final impurities LiTiOPO4 and Li4P2O7. This unified mechanism provides important insights on the enhanced densification of LATP at lower temperatures with the use of Li salt sintering aids.

Correction for ‘Capturing and labeling CO 2 in a jar: mechanochemical 17 O-enrichment and ssNMR study of sodium and potassium (bi)carbonate salts’ by Austin Peach et al. , Chem. Sci. , 2025, 16 , 10731–10741, https://doi.org/10.1039/D4SC08491H.

This chapter describes the use of NMR crystallography for the study of disordered inorganic solids. After briefly discussing the different types of disorder that are encountered in these materials and approaches for modelling disorder, recent advances in the application to systems including minerals, biomaterials, ceramics, energy materials and porous solids are presented. The additional challenges posed by systems exhibiting dynamic disorder are also discussed before the future outlook in this area is considered.

With the rapid increase in temperatures around the planet, the need to develop efficient means to reduce CO2 emissions has become one of the greatest challenges of the scientific community. Many different strategies are being studied worldwide, one of which consists of trapping the gas in porous materials, either for its short- or long-term capture and storage, or its re-use for the production of value-added compounds. Yet, to further the development of such systems, there is a real need to fully understand their structure and properties, including at the molecular-level following the physisorption and/or chemisorption of CO2 (which can lead to various species, including carbonate and bicarbonate ions). In this context, 17O NMR naturally appears as the analytical tool of choice, because of its exquisite sensitivity to probe subtle differences in oxygen bonding environments. To date, it has scarcely been used, due to the very low natural abundance of 17O (0.04%), and the difficulty in purchasing or obtaining commercial 17O-labeled compounds adapted to such investigations (e.g., 17O-CO2(g), or 17O-enriched Na- and K-(bi)carbonate salts, which can be readily transformed into CO2). Herein, we demonstrate how, using mechanochemistry, it is possible to enrich with 17O a variety of Na- and K-(bi)carbonate salts in a fast, economical, scalable, and user-friendly way. The high enrichment levels enabled recording the first high-resolution 17O ssNMR spectra of these phases at different temperatures and magnetic fields. From these, the typical spectral signatures of (bi)carbonate ions could be obtained, showing their strong sensitivity to local environments and dynamics. Lastly, we show how thanks to the selective 17O-labeling, other aspects of the reactivity of carbonates in materials can be unveiled using in situ 17O ssNMR. In the long run, it is expected that this work will open the way to more profound investigations of the structure and properties of carbon capture and storage systems, and, more generally speaking, of functional materials containing carbonates.

The discovery of solute precursors of crystalline materials, such as biominerals, recently challenged the classical nucleation theory (CNT). One emerging method for investigating these early-stage intermediates in solution is dissolution dynamic nuclear polarization (dDNP)-enhanced nuclear magnetic resonance (NMR) spectroscopy. Recent applications of dDNP to calcium carbonate (CaC) and calcium phosphate (CaP) mineralization have demonstrated the feasibility of identifying and tracing very early-stage prenucleation clusters (PNCs). However, the structural details remain difficult to resolve as dDNP is mainly limited to simple one-dimensional NMR detection. To overcome this bottleneck, we herein integrate hyperpolarized NMR of PNC with molecular dynamics simulations and quantum mechanical calculations to gain atomistic structural insights into CaP PNCs. By simulating the PNC structures, computing chemical shift parameters, and comparing these to hyperpolarized NMR "fingerprint" spectra, we demonstrate how to derive models of solution-state structural ensembles of PNC, even when very short-lived. With this approach, we find that the Ca/Pi ratio inside PNC tends to stay close to 1 independent of pH, while their sizes vary, leading to larger precursors under more basic conditions. At the same time, phosphate speciation within PNC was found to be independent of pH, as only monohydrogen phosphates participated in PNC formation. This latter feature also entailed a pH-independent local atomistic arrangement of phosphates coordinating a Ca(II) center, leading to constant Ca2+-Pi distances of ∼3 and ∼3.6 Å. These ion-to-ion distances agree with those found inside solid CaP phases such as brushite, octacalcium phosphate, or hydroxyapatite─a feature hinting toward the templating function of PNCs. Thus, our method (i) extends the methodological scope of hyperpolarized NMR by complementing one-dimensional fingerprint spectra with full structural models and (ii) sheds light on key intermediates that have been experimentally underexplored.

Boron carbide (B4+delta C) possesses a large potential as a structural material owing to its lightness, refractory character, and outstanding mechanical properties. However, its large-scale industrialization is set back by its tendency to amorphize when subjected to an external stress. In the present work, we design a path toward nanostructured boron carbide with greatly enhanced hardness and resistance to amorphization. The reaction pathway consists of triggering an isomorphic transformation of covalent nanocrystals of Na1-x B5-x C1+x (x = 0.18) produced in molten salts. The resulting 10 nm B4.1C nanocrystals exhibit a 4-fold decrease of size compared to previous works. Solid-state 11B and 13C NMR coupled to density functional theory (DFT) reveal that the boron carbide nanocrystals are made of a complex mixture of atomic configurations, which are located at the covalent structural chains between B11C icosahedral building units. These nanocrystals are combined with a spark plasma-sintering-derived method operated at high pressure. This yields full densification while maintaining the particle size. The nanoscaled grains and high density of grain boundaries provide the resulting nanostructured bodies with significantly enhanced hardness and resistance to amorphization, thus delivering a superhard material.

The introduction of phosphorus and nitrogen atoms in carbo-catalysts is a common way to tune the electronic density, and thereby the reactivity, of the material, as well as to introduce surface reactive sites. Numerous environments are reported for the N atoms, but the P-doping chemistry is less explored and focuses on surface POx groups. A one-step synthesis of P/N-doped carbonaceous materials is presented here, using affordable and industrially available urea and tetrakis(hydroxymethyl)phosphonium chloride (THPC) as the N and P sources, respectively. In contrast to most of the synthetic pathways toward P-doped carbonaceous materials, the THPC precursor only displays P-C bonds along the carbon backbone. This resulted in unusual phosphorus environments for the materials obtained from direct thermal treatment of THPC-urea, presumably of type C-P-N according to 31P NMR and XPS. Alternatively, the in situ polymerization and calcination of the precursors were run in calcium chloride hydrate, used as a combined reaction medium and porogen agent. Following this salt-templating strategy led to particularly high phosphorus contents (up to 18 wt%), associated with porosities up to 600 m2 g-1. The so-formed P/N-doped porous materials were employed as metal-free catalysts for the mild oxidative dehydrogenation of N-heterocycles to N-heteroarenes at room temperature and in air. Calcination of THPC-urea in metal chloride hydrate salt affords porous P/N-doped carbonaceous materials (up to 18 wt% [P]), used as oxidative dehydrogenation catalysts.

Octacalcium phosphate (OCP, Ca8(PO4)4(HPO4)2.5H2O) is a notable calcium phosphate due to its biocompatibility, making it a widely studied material for bone substitution. It is known to be a precursor of bone mineral, but its role in biomineralisation remains unclear. While the structure of OCP has been the subject of thorough investigations (including using Rietveld refinements of X-ray diffraction data, and NMR crystallography studies), important questions regarding the symmetry and H-bonding network in the material remain. In this study, it is shown that OCP undergoes a lowering of symmetry below 200 K, evidenced by 1H, 17O, 31P and 43Ca solid state NMR experiments. Using ab-initio molecular dynamics (MD) simulations and Gauge Including Projected Augmented Wave (GIPAW) DFT calculations of NMR parameters, the presence of rapid motions of the water molecules in the crystal cell at room temperature is proved. This information leads to an improved description of the OCP structure at both low and ambient temperatures, and helps explain long-standing issues of symmetry. Remaining challenges related to the understanding of the structure of OCP are then discussed.

The stability of metal-organic frameworks (MOFs) in the presence of water is crucial for a wide range of applications, including the production of freshwater, desiccation, humidity control, heat pumps/chillers and capture and separation of gases. In particular, their stability under steam flow is essential since most industrial streams contain water vapor. Nevertheless, to the best of our knowledge, the stability under steam flow of Zr-based MOFs, which are among the most widely studied MOFs, has not been investigated so far. We explore it herein for three UiO-like Zr-based MOFs built from the same Zr cluster but distinct organic linkers at temperature ranging from 80 to 200 degrees C. We demonstrate the possibility of acquiring their 91Zr NMR spectra using high magnetic field (18.8 T) and low temperature (140 K) and of interpreting them by comparing experimental data with NMR parameters calculated by DFT. NMR observation of this challenging isotope combined with more conventional techniques, such as N2 adsorption, X-ray diffraction, IR, and 1H and 13C solid-state NMR spectroscopies, provides information not only on the possible collapse of the MOF framework but also on the adsorption of molecules into the pores. We notably show that UiO-66(Zr) and UiO-66-Fum(Zr) built from terephthalate and fumarate linkers, respectively, are stable over 24 h (and even over 7 days for UiO-66(Zr)) under steam flow at all investigated temperatures, whereas UiO-67-NH2 containing a 2-amino-[1,1 '-biphenyl]-4,4 '-dicarboxylate linker degrades under steam flow at temperatures ranging from 80 to 150 degrees C but is preserved at 200 degrees C. The lower stability of UiO-67-NH2 stems from its larger pores and its weaker Zr-O coordination bonds, whereas its preservation at 200 degrees C results from a more limited condensation of water in the pores.

The phosphorescence of boric acid (BA, H3BO3) at room temperature is a puzzling phenomenon subject to controversial interpretations although the role of structural defects has not yet been considered. Heat treatments of boric acid cause its transformation into the metaboric phase and amorphous boron oxide (B2O3). The structural changes after thermal processing can create defects that become centers of luminescence and recombination channels in the visible range. In the present work, commercial boric acid is thermally processed at different temperatures. Samples treated between 200 and 400 degrees C exhibit remarkable phosphorescence in the visible range. At approximate to 480 and 528 nm, two distinct phosphorescent emissions occur, associated with trapped charge carriers recombinations identified by thermoluminescence (TL) and electron paramagnetic resonance spectroscopy (EPR). The structural and optical studies suggest that the activation of boric acid phosphorescence after heat treatment is correlated with the presence of defects. The afterglow results from a trapping and detrapping process, which delays the recombination at the active optical centers. Time-dependent density functional study (DFT) of defective BOH molecules and clusters shows the emergence of near UV and blue optical transitions in absorption. These defects trigger the photoluminescence in thermally processed boric acid samples. Boric acid emits phosphorescence in visible range only after dehydration and melting. Defects activate two distinct phosphorescent emissions, with trapping and detrapping process delaying recombination at active optical centers. Time-dependent density functional study reveals near UV and blue optical transitions in absorption due to oxygen vacancies and non-bridging oxygens, triggering photoluminescence.image

VAT photopolymerization technology was applied to fabricate three-dimensional (3D) porous beta-Ca2SiO4 ceramic scaffolds functionalized with graphene oxide (GO) sheets decorated with silver nanoparticles (AgNPs). We achieved this by utilizing commercial resin blends and "customized" resin both loaded with CaCO3 particles. The dual functionality of the "customized" resin, which serves as both a preceramic polymer and photocurable resin, is exploited. To assess the properties of these ceramics, we carried out an in-depth comparative analysis using a combination of spectroscopic, microscopic and analytical techniques. After annealing at 1200 degrees C, the as-prepared ceramics achieved a relative density of 65% leading to high compressive strength (approximate to 40 MPa). Importantly, beta-Ca2SiO4 ceramic scaffolds demonstrated good in vitro bioactivity by promoting hydroxyapatite formation. When subjected to E. coli, scaffolds functionalized with AgNPs/GO showed higher antibacterial activity than their non-functionalized counterparts. Moreover, ceramic scaffolds derived from the "customized" resin exhibited sixfold higher antimicrobial activity than scaffolds made from commercial resin mixtures. To assess biocompatibility, we conducted in vitro studies using mesenchymal stem cells (MSCs) culture. Encouragingly, all bioceramics proved non-cytotoxic and accelerated the proliferative rate of MSCs compared with the control. After 7 days in culture, cells showed a well-spread morphology with no obvious differences, clearly indicating that bioceramic scaffolds actively promote cell adhesion and viability. Overall, due to their interconnected porosity, excellent biomineralization, mechanical, antibacterial and cytocompatibility properties, these 3D-printed scaffolds hold significant promise as candidates for applications in hard tissue engineering. VAT photopolymerization technology was applied to fabricate three-dimensional (3D) porous beta-Ca2SiO4 ceramic scaffolds functionalized with graphene oxide (GO) sheets decorated with silver nanoparticles (AgNPs).

Calcium ion complexation in aqueous solutions is of paramount importance in biology as it is related to cell signaling, muscle contraction, or biomineralization. However, Ca2+-complexes are dynamic soluble entities challenging to describe at the molecular level. Nuclear magnetic resonance appears as a method of choice to probe Ca2+-complexes. However, Ca-43 NMR exhibits severe limitations arising from the low natural abundance coupled to the low gyromagnetic ratio and the quadrupolar nature of Ca-43, which overall make it a very unreceptive nucleus. Here, we show that Ca-43 dynamic nuclear polarization (DNP) NMR of Ca-43-labeled frozen solutions is an efficient approach to enhance the NMR receptivity of Ca-43 and to obtain structural insights about calcium ions complexed with representative ligands including water molecules, ethylenediaminetetraacetic acid (EDTA), and l-aspartic acid (l-Asp). In these conditions and in combination with numerical simulations and calculations, we show that( 43)Ca nuclei belonging to Ca2+ complexed to the investigated ligands exhibit rather low quadrupolar couplings (with CQ typically ranging from 0.6 to 1 MHz) due to high symmetrical environments and potential residual dynamics in vitrified solutions at a temperature of 100 K. As a consequence, when H-1 -> Ca-43 cross-polarization (CP) is used to observe Ca-43 central transition, "high-power" nu(RF)(Ca-43) conditions, typically used to detect spin 1/2 nuclei, provide similar to 120 times larger sensitivity than "low-power" conditions usually employed for detection of quadrupolar nuclei. These "high-power" CPMAS conditions allow two-dimensional (2D) H-1-Ca-43 HetCor spectra to be readily recorded, highlighting various Ca2+-ligand interactions in solution. This significant increase in Ca-43 NMR sensitivity results from the combination of distinct advantages: (i) an efficient H-1-mediated polarization transfer from DNP, resembling the case of low-natural-abundance spin 1/2 nuclei, (ii) a reduced dynamics, allowing the use of CP as a sensitivity enhancement technique, and (iii) the presence of a relatively highly symmetrical Ca environment, which, combined to residual dynamics, leads to the averaging of the quadrupolar interaction and hence to efficient high-power CP conditions. Interestingly, these results indicate that the use of high-power CP conditions is an effective way of selecting symmetrical and/or dynamic Ca-43 environments of calcium-containing frozen solution, capable of filtering out more rigid and/or anisotropic Ca-43 sites characterized by larger quadrupolar constants. This approach could open the way to the atomic-level investigation of calcium environments in more complex, heterogeneous frozen solutions, such as those encountered at the early stages of calcium phosphate or calcium carbonate biomineralization events.

Oxalate ligands are found in many classes of materials, including energy-storage materials and biominerals like hydrated calcium-oxalates. Determining their local environments at the atomic scale is thus paramount to establishing the structure and properties of numerous phases. Here, we show that high-resolution 17O solid-state NMR is a valuable asset for investigating the structure of crystalline oxalate systems. First, an efficient 17O-enrichment procedure of oxalate ligands is demonstrated using mechanochemical saponification. Then, the use of 17O-enriched oxalates for the synthesis of the biologically relevant calcium-oxalate monohydrate (COM) phase is presented, enabling the analysis of its structure and heat-induced phase transitions by high-resolution 17O solid-state NMR. NMR studies of the low-temperature COM form (LT-COM), using magnetic fields varying from 9.4 to 35.2 T, as well as 13C-17O MQ/D-RINEPT and 17O{1H} MQ/REDOR experiments, enabled the 8 inequivalent oxygen sites of the oxalate ligands to be resolved, with a tentative assignment proposed. Then, the structural changes occurring upon heat treatment of COM were followed by high-resolution 17O solid-state NMR, providing new insight into the structures of the high-temperature form (HT-COM) and anhydrous calcium oxalate alpha-phase (alpha-COA), including the presence of structural disorder in the latter case. Overall, this work highlights the ease associated with 17O-isotopic enrichment of oxalate oxygens, and how it enables the study of oxalate structures (including materials of biological relevance) at high-resolution via solid-state NMR, in the frame of “NMR-crystallography” investigations.

Mixed-anion compounds widen the chemical space of attainable materials compared to single anionic compounds, but the exploration of their structural diversity is limited by common synthetic paths. Especially, oxychlorides rely mainly on layered structures, which suffer from low stability during photo(electro)catalytic processes. Herein we report a strategy to design a new polar 3D tetrahedral framework with composition Zn4 Si2 O7 Cl2 . We use a molten salt medium to enable low temperature crystallization of nanowires of this new compound, by relying on tetrahedral building units present in the melt to build the connectivity of the oxychloride. These units are combined with silicon-based connectors from a non-oxidic Zintl phase to enable precise tuning of the oxygen content. This structure brings high chemical and thermal stability, as well as strongly anisotropic hole mobility along the polar axis. These features, associated with the ability to adjust the transport properties by doping, enable to tune water splitting properties for photoelectrocatalytic H2 evolution and water oxidation. This work then paves the way to a new family of mixed-anion solids.

The possibility of enriching in 17O the water molecules within hydrated biominerals belonging to the Ca-pyrophosphate family was investigated, using liquid assisted grinding (LAG) in the presence of 17O-labelled water. Two phases with different hydration levels, namely triclinic calcium pyrophosphate dihydrate (Ca2P2O7·2H2O, denoted t-CPPD) and monoclinic calcium pyrophosphate tetrahydrate (Ca2P2O7·4H2O, denoted m-CPPT β) were enriched in 17O using a "post-enrichment" strategy, in which the non-labelled precursors were ground under gentle milling conditions in the presence of stoichiometric quantities of 17O-enriched water (introduced here in very small volumes ∼10 μL). Using high-resolution 17O solid-state NMR (ssNMR) analyses at multiple magnetic fields, and dynamic nuclear polarisation (DNP)-enhanced 17O NMR, it was possible to show that the labelled water molecules are mainly located at the core of the crystal structures, but that they can enter the lattice in different ways, namely by dissolution/recrystallisation or by diffusion. Overall, this work sheds light on the importance of high-resolution 17O NMR to help decipher the different roles that water can play as a liquid-assisted grinding agent and as a reagent for 17O-isotopic enrichment.