Angle Spinning Nuclear Magnetic Resonance Research Articles

Ni phosphide catalysts on Al2O3‐zeolite prepared by phosphidation for methyl palmitate hydroconversion

AbstractBACKGROUNDOne‐stage hydroconversion of fatty‐acid based feedstocks is a promising way to obtain high‐quality fuels. This process is based on hydrodeoxygenation, isomerization and hydrocracking reactions. In this work, Ni2P/Al2O3‐zeolite catalysts were synthesized and tested in hydroconversion of a model compound – methyl palmitate.RESULTSNi2P catalysts were prepared by in situ phosphidation of metallic Ni/Al2O3‐zeolite precursors by PPh3. Mixtures of zeolite (30 wt%) and boehmite were peptized and extruded to obtain the support granules. SAPO‐11, ZSM‐5, ZSM‐22, ZSM‐23 and ZSM‐12 were used as a zeolite component. The catalysts and supports were characterized by a range of physicochemical methods: chemical analysis (ICP‐AES), low‐temperature N2 adsorption, H2‐temperature programmed reduction, NH3‐temperature programmed desorption, Fourier transform infrared spectroscopy of adsorbed CO, X‐ray diffraction, transmission electron microscopy, X‐ray photoelectron spectroscopy, and 27Al and 31P magic angle spinning nuclear magnetic resonance. The catalysts were studied in methyl palmitate hydroconversion (one‐stage hydrodeoxygenation‐isomerization‐hydrocracking) in a continuous‐flow fixed bed reactor at 290–340 °C, 2 MPa, H2/feed = 600 Ncm3/cm3 and LHSV = 5.3 h−1. SAPO‐11 containing sample showed high selectivity to C15 and C16 iso‐alkanes (63%, at 340 °C), and all ZSM‐containing samples showed high selectivity to cracked C5–C9 products (55–100%, at 340 °C) with varying amounts of iso‐alkanes (31–57%, at 340 °C).CONCLUSIONThe results show that by choosing the zeolite component of the catalyst it is possible to finely tune product quality in the range from low‐temperature diesel fuel to jet fuel or gasoline. © 2024 Society of Chemical Industry (SCI).

Wide-pore fully porous mixed-mode octyl/pyridyl-bonded silica material with pH-dependent surface charge reversal for high-performance hydrophobic charge-induction chromatography of proteins

In an attempt to overcome silanophilic interactions like observed on popular reversed-phase butyl-bonded silica stationary phases in protein HPLC, a mixed-mode stationary phase based on wide pore silica (3 µm, 300 Å) was prepared by co-immobilization of octyl and 2-(2-pyridyl)ethyl ligands. The surface modification was performed by a new approach using synthesized functional silatranes of the above ligands and prewetted silica. It allowed to generate a dense polymeric siloxane layer on the silica surface. Butyl-bonded silica and octyl/3-aminopropyl-bonded mixed-mode silica phases were prepared for comparison. The modified silicas were subsequently characterized by elemental analysis regarding ligand densities, by solid-state 29Si and 13C cross polarization/magic angle spinning nuclear magnetic resonance spectroscopy for confirming the surface-bonded structure, and by pH-dependent ζ-potential measurements via electrophoretic light scattering providing net surface charge information at distinct pH values. While the classical butyl-bonded stationary phase revealed negative ζ-potential over the entire pH range investigated (pH 3.5-9.5) due to residual silanols and the mixed-mode octyl/3-aminopropyl-bonded silica positive ζ-potential over the entire pH range, pH-dependent charge reversal was observed at approximately pH 5.5 for the octyl/pyridyl-bonded stationary phase. Then, a test set of proteins differing in hydrophobicities and isoelectric points was employed to evaluate the retention characteristics of all three synthesized stationary phases over the pH range of 3 to 7.5 by acetonitrile-gradient elution reversed-phase HPLC. Under acidic conditions (pH 3) the mixed-mode phases octyl/pyridyl-silica and octyl/aminopropyl-silica showed reduced retention and improved peak shapes due to repulsive interactions preventing silanophilic interactions, while protein separations by their hydrophobicities were achieved (repulsive charge-assisted protein RPLC). Finally, the prepared novel mixed-mode octyl/pyridyl-bonded stationary phase was evaluated in hydrophobic charge induction chromatography mode for protein separation of the same test set. Instead of an organic modifier gradient, elution was enforced by a pH gradient from pH 7.5 to 3 at constant organic modifier content of 10%. This chromatographic mode showed orthogonal retention characteristics and reversed elution order compared to above organic gradient RP-HPLC. In addition, significantly less organic solvent was used under these conditions, classifying it as a green protein LC technology.

Effect of lithium concentration on the network connectivity of nuclear waste glasses

Structure of borosilicate glasses with varying Li2O contents were investigated using Magic Angle Spinning (MAS) Nuclear Magnetic Resonance (NMR), employing 6Li, 11B, 23Na, 27Al and 29Si nuclei. 11B MAS NMR revealed that increasing Li2O contents result in formation of [BO4]− sites at the expense of BO3. 11B{6Li} and 27Al{6Li} dipolar heteronuclear multiple quantum correlation (D-HMQC) NMR revealed Li as a charge compensator for anionic tetrahedral sites with increased Li. 11B{6Li} J-coupling mediated HMQC NMR suggested the possible association of Li with non-bridging oxygens on Q2 and Q3 sites, indicating its dual role in the glass network. 29Si and 23Na MAS NMR spectra showed depolymerisation of the silicate network and shortening of Na-O bond lengths with increased Li. NMR results are supported by Raman spectroscopy and thermal analysis that indicate depolymerisation of the silicate network and a reduction in glass transition temperature at higher Li content.

A New Class of Oxyhalide Solid Electrolytes NaNbCl6-2xOx for Solid-state Sodium Batteries.

Sodium-based batteries are gaining momentum due to the abundance and lower cost of sodium compared to lithium. Solid-state sodium batteries can also provide further safety advantages. However, sodium-based solid-state electrolytes (SSEs) that meet all the rigorous requirements, such as high ionic conductivity, oxidative stability with the cathode, and ease of processability, are lacking. We present here a new class of sodium-based oxyhalide electrolytes NaNbCl6-2xOx with a facile mechanochemical synthesis. The oxyhalide NaNbCl4O exhibits close to two orders of magnitude higher ambient-temperature sodium-ion conductivity (1.03 x 10-4 S cm-1) compared to the halide counterpart NaNbCl6 (3 x 10-6 S cm-1). Structural motifs unique to the oxygen content in NaNbCl6-2xOx are identified with 23Na and 93Nb magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy and x-ray diffraction (XRD). Solid-state sodium batteries assembled with NaNbCl4O electrolyte and the cobalt- and nickel-free layered Na0.70Fe0.3Mn0.65Al0.05O2 cathode exhibit a maximum discharge capacity of 155 mA h g-1 with good cycle life at ambient temperature.

A New Class of Oxyhalide Solid Electrolytes NaNbCl6‐2xOx for Solid‐state Sodium Batteries

Sodium‐based batteries are gaining momentum due to the abundance and lower cost of sodium compared to lithium. Solid‐state sodium batteries can also provide further safety advantages. However, sodium‐based solid‐state electrolytes (SSEs) that meet all the rigorous requirements, such as high ionic conductivity, oxidative stability with the cathode, and ease of processability, are lacking. We present here a new class of sodium‐based oxyhalide electrolytes NaNbCl6‐2xOx with a facile mechanochemical synthesis. The oxyhalide NaNbCl4O exhibits close to two orders of magnitude higher ambient‐temperature sodium‐ion conductivity (1.03 x 10‐4 S cm‐1) compared to the halide counterpart NaNbCl6 (3 x 10‐6 S cm‐1). Structural motifs unique to the oxygen content in NaNbCl6‐2xOx are identified with 23Na and 93Nb magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy and x‐ray diffraction (XRD). Solid‐state sodium batteries assembled with NaNbCl4O electrolyte and the cobalt‐ and nickel‐free layered Na0.70Fe0.3Mn0.65Al0.05O2 cathode exhibit a maximum discharge capacity of 155 mA h g‐1 with good cycle life at ambient temperature.

Integrating HRMAS-NMR Data and Machine Learning-Assisted Profiling of Metabolite Fluxes to Classify Low- and High-Grade Gliomas.

Diagnosing and classifying central nervous system tumors such as gliomas or glioblastomas pose a significant challenge due to their aggressive and infiltrative nature. However, recent advancements in metabolomics and magnetic resonance spectroscopy (MRS) offer promising avenues for differentiating tumor grades both in vivo and ex vivo. This study aimed to explore tissue-based metabolic signatures to classify/distinguish between low- and high-grade gliomas. Forty-six histologically confirmed, intact solid tumor samples from glioma patients were analyzed using high-resolution magic angle spinning nuclear magnetic resonance (HRMAS-NMR) spectroscopy. By integrating machine learning (ML) algorithms, spectral regions with the most discriminative potential were identified. Validation was performed through univariate and multivariate statistical analyses, along with HRMAS-NMR analyses of 46 paired plasma samples. Amongst the various ML models applied, the logistics regression identified 46 spectral regions capable of sub-classifying gliomas with accuracy 87% (F1-measure 0.87, Precision 0.82, Recall 0.93), whereas the extra-tree classifier identified three spectral regions with predictive accuracy of 91% (F1-measure 0.91, Precision 0.85, Recall 0.97). Wilcoxon test presented 51 spectral regions significantly differentiating low- and high-grade glioma groups (p < 0.05). Based on sensitivity and area under the curve values, 40 spectral regions corresponding to 18 metabolites were considered as potential biomarkers for tissue-based glioma classification and amongst these N-acetyl aspartate, glutamate, and glutamine emerged as the most important markers. These markers were validated in paired plasma samples, and their absolute concentrations were computed. Our results demonstrate that the metabolic markers identified through the HRMAS-NMR-ML analysis framework, and their associated metabolic networks, hold promise for targeted treatment planning and clinical interventions in the future.

Resolving intermediates during the growth of aluminum deuteroxide (Hydroxide) polymorphs in high chemical potential solutions

Aluminum hydroxide polymorphs are of widespread importance yet their kinetics of nucleation and growth remain beyond the reach of current models. Here we attempt to unveil the reaction processes underlying the polymorphs formation at high chemical potential. We examine their formation in-situ from supersaturated alkaline sodium aluminate solutions using deuteration and time-resolved neutron pair distribution function analyses, which indicate the formation of individual Al(OD)3 layers as an intermediate particle phase. These layers ultimately stack to form gibbsite- or bayerite-like layered heterostructures. Ex-situ characterization of the recovered precipitates using 27Al magic angle spinning nuclear magnetic resonance spectroscopy, Raman, X-ray diffraction, and scanning electron microscopy, suggests the presence of additional intermediate states, an amorphous compound bearing both tetrahededrally- and penta-coordinated Al3+. These observations reveal the complex pathways to form Al(OD)3 monolayers via either transient pentacoordinate species or amorphous-to-ordered transitions. The subsequent crystallization of admixed gibbsite/bayerite is followed by an Al(OD)3 monolayer attachment process.

Atomic scale investigation and cytocompatibility of copper and zinc-loaded Phosphate-Based Glasses Prepared by Coacervation

Phosphate-based glasses (PBGs) are bioresorbable materials that find application in the field of controlled drug delivery and tissue engineering. The structural arrangements of the phosphate units in PBGs, along with the knowledge of how therapeutic metallic ions are embedded in the phosphate network are important in understanding the degradation and targeted release properties of these materials. Using a combination of Raman spectroscopy, high-energy X-ray diffraction and 31P and 23Na solid-state magic angle spinning nuclear magnetic resonance, the atomic structure of coacervate PBGs in the system P2O5-CaO-Na2O-MOx (M = Cu or Zn) with loadings of 2, 10 and 15 mol % of M2+ have been studied as functions of composition and calcination temperature. After drying at room temperature, the structures of the phosphate network in PBG-Cu and PBG-Zn are quite similar, with that of PBG-Zn exhibiting slightly higher connectivity. Heating at 300°C causes degradation of the polyphosphate chains, even though Q2 species remain predominant. X-ray photoelectron spectroscopy demonstrates that Cu in calcined PBGs is present in both oxidation states +1 and +2, with a predominance of the +2 state. Cu and Zn ions release data after 24 h exposure of PBGs in deionized water and cell medium DMEM show that release is proportional to their loadings. Cytotoxicity MTT assays of dissolution products of PBG-Cu/ZnX calcined at 300 °C on human osteoblast cells (MG63) and on human skin cells (HaCaTs) showed good cellular response for all compositions, indicating that PBGs have great potential for both hard and soft tissue regeneration.

ZnH2P4N8: Case Study on Topochemical Imidonitridophosphate High-Pressure Synthesis.

Nitridophosphates are subject of current research, as they have a broad spectrum of properties and potential applications, such as ion conductors or luminescent materials. Yet, the subclass of imidonitridophosphates has been studied less extensively. The primary reason is that the controlled N-H functionalization of nitridophosphates is not straight forward, making targeted synthesis more challenging. Inspired by the high-pressure (HP) post-synthetic modification of nitridophosphates, we present the topochemical HP deprotonation of phosphorus nitride imides using the high-pressure polymorph β-PN(NH) as an example. Additional incorporation of Zn2+ results in the first quaternary transition metal imidonitridophosphate ZnH2P4N8. The crystal structure was elucidated by single-crystal X-ray diffraction (SCXRD), energy-dispersive X-ray spectroscopy (EDX), powder X-ray diffraction (PXRD) and solid-state magic angle spinning nuclear magnetic resonance spectroscopy (MAS NMR). In addition, the presence of H as part of an imide group was confirmed by IR spectroscopy. The potential of this defunctionalization approach for controlling the N-H content is demonstrated by the preparation of partially deprotonated intermediates ZnxH4-2xP4N8 (x≈ 0.5, 0.85). This topochemical high-pressure reaction represents a promising way to prepare, control and manipulate new imide-based materials without altering their overall anionic framework.

High-Resolution Magic Angle Spinning Nuclear Magnetic Resonance Spectroscopy of Paired Clinical Liver Tissue Samples from Hepatocellular Cancer and Surrounding Region.

The global burden of liver cancer is increasing. Timely diagnosis is important for optimising the limited available treatment options. Understanding the metabolic consequences of hepatocellular carcinoma (HCC) may lead to more effective treatment options. We aimed to document metabolite differences between HCC and matched surrounding tissues of varying aetiology, obtained at the time of liver resection, and to interpret metabolite changes with clinical findings. High-resolution magic angle spinning nuclear magnetic resonance (HRMAS-NMR) spectroscopy analyses of N = 10 paired HCC and surrounding non-tumour liver tissue samples were undertaken. There were marked HRMAS-NMR differences in lipid levels in HCC tissue compared to matched surrounding tissue and more subtle changes in low-molecular-weight metabolites, particularly when adjusting for patient-specific variability. Differences in lipid-CH3, lipid-CH2, formate, and acetate levels were of particular interest. The obvious differences in lipid content highlight the intricate interplay between metabolic adaptations and cancer cell survival in the complex microenvironment of liver cancer. Differences in formate and acetate might relate to bacterial metabolites. Therefore, documentation of metabolites in HCC tissue according to histology findings in patients is of interest for personalised medicine approaches and for tailoring targeted treatment strategies.

Interaction between peptide and solid lignin suggest mechanisms of abiotic covalent bond formation

The mechanisms behind the formation of soil organic matter (SOM) and associated nitrogen immobilization remain partially elusive, while ongoing research continues to shed light on carbon and nitrogen sequestration in the environment. Studies show that quinone-like structures within alkali-soluble humic extracts of SOM can bond covalently with nitrogen-containing molecules derived from proteinaceous organic matter. However, direct molecular evidence for this chemical bonding with lignin in the solid form and non-solvent-extracted SOM is lacking. Using gel-state 1H-15N heteronuclear single quantum coherence (HSQC) high-resolution magic angle spinning (HRMAS) nuclear magnetic resonance (NMR) spectroscopy, we demonstrate that a 15N-labeled peptide (glycine-glycine-glycine-arginine, GGGR), can covalently bind to solid, untreated, brown rotted wood as well as 1,2-naphthoquinone, a quinone-model molecule typically found in degraded lignin. The new peaks in both reactions represent a change in the environment surrounding the N-functional groups. Interaction of the 15N-labeled peptide with the model quinone produced NMR cross peaks that are similar to those of the solid lignin. This suggests that the quinone-like structures are the most likely functional groups to form covalent bonds with peptides in the degraded lignin. Both Michael addition and Schiff base formation is proposed when the peptide GGGR interacts with white oak lignin and 1,2-naphthoquinone. These processes are of considerable importance to N incorporation into SOM and offer insights into how proteinaceous molecules could potentially be preserved and sequestered through covalent bond formation.

Synthesis methodology of pure N–A–S–H gels with wide range of Si/Al ratios at ambient temperature

AbstractThis study presents the development of a synthesis route for sodium aluminosilicate hydrate (N–A–S–H) gels with various Si/Al ratios carried out at ambient temperature. The synthesis is based on a simple “sol–gel” method, where commercial reactants are used to provide highly reactive Si and Al sources. Comprehensive characterization, including scanning electron microscope‐energy‐dispersive spectroscopy (SEM‐EDS), gas pycnometry, inductively coupled plasma (ICP), X‐ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), X‐ray diffraction (XRD), and magic angle spinning (MAS) nuclear magnetic resonance (NMR) (27Al, 23Na, 29Si, and 1H), is employed to verify the morphology, density, chemical composition, long‐range order, and local structure of the gels. Our results show that the synthesized gels are pure, amorphous, and homogeneous with Si/Al final ratio ranging from 1.22 to 2.23. Structural analysis of the gels indicates the synthesis of compounds with high degree of geopolymerization, which are representative of N–A–S–H gel formed in sodium‐based geopolymers.

Fabrication of polydopamine-modified cellulose hydrogel for controlled release of α-mangostin.

Hydrogels are notable for their outstanding absorbent qualities, satisfactory compatibility with biological systems, ability to degrade, and inherent safety, all of which contribute to their high demand in the field of biomedicine. This study focuses on the fabrication of hydrogels using environmentally friendly cellulosic material. Cellulose hydrogel beads were prepared by physical cross-linking in a NaOH/urea medium. Furthermore, nano polydopamine was integrated into the hydrogel matrix as functional polymers and α-mangostin was employed as an active pharmaceutical ingredient. The physicochemical properties were comprehensively analyzed using Fourier-transform infrared spectrometer, 13C cross-polarization/magic angle spinning nuclear magnetic resonance, thermogravimetric analysis, and scanning electron microscope. The drug delivery properties, including water content, swelling ratio, and drug release profiles, were evaluated. In vitro cytotoxicity against MC3T3-E1 cells was assessed using sulforhodamine B staining. All test hydrogels exhibited inhibitory activity against the growth of MC3T3-E1 cells. These results indicated the potential use of these hydrogels as a drug delivery carrier for α-mangostin in the treatment of ankylosing spondylitis.

High-resolution magic angle spinning nuclear magnetic resonance of donor pancreatic tissue may predict islet viability prior to isolation.

For patients with type 1 diabetes mellitus complicated by severe hypoglycemia, clinical islet transplantation is an efficacious alternative to whole pancreas transplantation. While islet transplantation has improved over the last few years, there remain questions regarding its cost-effectiveness and donor allosensitization, which is exacerbated when islets from more than one donor are required. Understanding the features of a pancreas that would provide viable islets prior to isolation may lead to development of an accurate assay that could identify suitable pancreases and provide significant cost savings to a clinical islet transplantation program. In this pilot study, solid-state high-resolution magic angle spinning (HRMAS) nuclear magnetic resonance (NMR) spectroscopy was used to assess samples of convenience of human pancreatic tissue taken prior to islet isolation both before and after incubation using the two-layer perfluorocarbon (PFC)/University of Wisconsin (UW) solution cold-storage method. We observed that, prior to incubation, human pancreatic tissue exhibited evidence of hypoxia with decreased peak integrals associated with glucose and increased peak integrals corresponding to lactate and free fatty acids. After incubation, we observed a reversal of the hypoxia-induced damage, as integrals corresponding to glucose increased, and those corresponding to lactate and free fatty acid resonances decreased. Interestingly, a significant correlation between the ratio of the glucose integral (at 3.0-4.5 ppm) to the sum of the fatty acid (at 0.9 ppm) and lactate + fatty acid (at 1.3 ppm) integrals and glucose responsiveness, a measure of islet viability, of the isolated islets, was observed after incubation in PFC/UW solution for pancreases that responded to PFC/UW solution incubation (p = 0.02). Notably, pancreases with little or no change in the integral ratio after PFC/UW solution incubation had poor recovery. These results suggest that tissue recovery is a key feature for determining islet cell viability, and further that HRMAS NMR may be a practical method to quickly assess human donor pancreatic tissue prior to islet isolation for clinical transplantation.

A sol-gel templating route for the synthesis of hierarchical porous calcium phosphate glasses containing zinc

Hierarchical porous phosphate-based glasses (PPG) have great potential in biomedicine. Micropores (pore size <2 nm) increase the surface area, mesopores (pore size 2–50 nm) facilitate the absorption and diffusion of therapeutic ions and molecules making them ideal controlled delivery systems, while macropores (pore size >50 nm) facilitate the movement and diffusion of cells and fluids. In addition, the bioresorbability of PPG allows for their complete solubility in body fluid, alongside simultaneous formation of new tissue. Making PPG via the traditional melt-quenching (MQ) synthesis method used for phosphate-based glasses (PG), is not straightforward. Hence, we present here a route for preparing such glasses using a combination of sol-gel (SG) and templating methods. Hierarchical PPG in the P2O5–CaO–Na2O system with the addition of 1, 3 and 5 mol % of Zn2+ were prepared with pore dimensions ranging from the micro-to the macro scales using Pluronic 123 (P123) as a surfactant. The presence of micropores (0.30–0.46 nm), mesopores (1.75–9.35nm) and macropores (163–207 nm) was assessed via synchrotron-based Small-Angle X-ray Scattering (SAXS), with the presence of the latter two confirmed by Scanning Electron Microscopy (SEM). Structural characterisation performed using 31P solid state magic angle spinning nuclear magnetic resonance (MAS NMR) and Fourier Transform Infrared (FTIR) spectroscopies shows the presence of Q2, Q1 and Q0 phosphate species with a predominance of Q1 species in all compositions. Dissolution studies in deionised (DI) water confirm that controlled release of phosphates, Ca2+, Na+ and Zn2+ is achieved over a period of 7 days. In particular, the release of Zn2+ is proportional to its loading, making its delivery particularly easy to control.

A Nanocrystalline ZSM‐5 for the Catalytic Cracking of Waste Cooking Oil

AbstractA series of hierarchical ZSM‐5 nanocrystalline aggregates (HNZ‐5) was synthesized using a hydrothermal method with tetrapropylammonium hydroxide as a structural guide. The HNZ‐5 samples having different Si/Al molar ratios all showed suitable hierarchical architectures and the maximum surface area was found to be 329 m2/g. The SEM image displayed the width of the individual crystal particles was ~100 nm, and its nanocrystalline clusters generated intercrystalline pores. Temperature‐programmed desorption with NH3 indicated that the total acidity of this material increased with increases in the Al3+ content to a maximum of 0.47 mmol/g at a Si/Al ratio of 15. In addition, 27Al magic angle spinning nuclear magnetic resonance spectra showed that the acid sites were associated with tetrahedral and octahedral Al sites. This HNZ‐5 was applied to the catalytic cracking of waste cooking oil model compound and gave a light olefin yield as high as 43.9 % at 550 °C. Extending the reaction time to 6000 min provided a yield of light olefins in excess of 30 %, which was higher than that achieved using traditional ZSM‐5. These data confirmed that the hierarchical pore structure of HNZ‐5 resulting from the self‐assembly of nanocrystals, together with exposed acidic sites, promoted the catalytic conversion of large molecules.

Low temperature phase transition mechanism of amorphous Al-oxalate to nano α-alumina

α-Alumina (α-Al2O3), widely used as a raw material or production in advanced manufacturing industry, has attracted much attention in terms of its preparation temperature. A simple dissolution-evaporation-precipitation process was employed to obtain the amorphous Al-oxalate (AAO) precursor, serving as the starting material for the low temperature preparation of nano α-Al2O3. The crystalline structure and thermal behavior of the AAO were compared with commercially available aluminum hydroxide (Al(OH)3) powder using the X-ray powder diffraction (XRD) instrument, the thermal gravity analysis and differential scanning calorimetry (TG-DSC). The phase transition mechanism of AAO was investigated by the fourier transform infrared spectroscopy (FTIR), transmission electron microscope (TEM), scanning electron microscope (SEM), and 27Al magic angle spinning nuclear magnetic resonance (27Al-MAS-NMR). The DSC results indicated that AAO underwent a phase transformation at 982 °C. The α-alumina diffraction peaks appeared in AAO at 1000 °C, while α-Al2O3 phase was observed for Al(OH)3 at 1200 °C. Furthermore, an absorption peak at 452 cm−1, corresponding to Al–O bond in α-alumina was detected at 1000 °C. The proposed low-temperature preparation mechanism of α-alumina from AAO is as follows: four coordination Al-oxalate species entities coexist within the AAO sample; with increasing temperature, organic acid functional groups oxidize and volatilize, resulting in the formation of tetra-coordinate [AlO4], penta-coordinate [AlO5], and hexa-coordinate [AlO6] atomic groups; these atomic clusters further polymerize to form a structurally dense α-alumina crystal at the nano-scale (∼50 nm) at around 1000 °C. The experimental findings present a novel approach and method for the low-temperature preparation of nano-sized alumina powder. Additionally, a feasible theoretical reference for the low-temperature phase transition mechanism of amorphous Al-oxalate was provided.

Monitoring the Geopolymerization Reaction of Geopolymer Foams Using 29Si and 27Al MAS NMR

This study aims to investigate the geopolymerization reaction of geopolymer foams produced with three different foaming agents: aluminum powder, zinc powder, and hydrogen peroxide. The geopolymerization reaction of geopolymer foam was monitored using the 27Al and 29Si magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy technique. 27Al MAS-NMR was used to monitor the reaction at an early stage, while 29Si and 27Al MAS-NMR analyses were employed at specific time intervals of 3, 6, 10, 15, and 28 days to examine the changes that occurred in the formed gel over time. We discussed in detail how the type of foaming agent used and the duration of the reaction both influence the quantity of gel formed and the amount of remnant fly ash. Our findings indicate that the type of foaming agent used affects the formation and structure of the gel, with aluminum powder leading to the highest gel formation. Additionally, the duration of the reaction plays a significant role in determining the quantity of remnant fly ash, with longer reaction times resulting in decreased fly ash content. This study sheds light on the relevance of understanding the role of foaming agents in the geopolymerization reactions of geopolymer foams and the influence of reaction time on the formed gel properties.

Mitigating Sodium Ordering for Enhanced Solid Solution Behavior in Layered NaNiO2 Cathodes.

The O-type layered nickel oxides suffer from undesired cooperative Jahn-Teller distortion stemming from Ni3+ ions and undergo multiple biphasic structural transformations during the insertion/extraction of large Na+ ions, posing a significant challenge to stabilize the structural integrity. We present here a systematic investigation of the impact of substituting 5 % divalent (Mg2+) or trivalent (Al3+ or Co3+) ions for Ni3+ to alleviate Na+ion ordering and perturb the Jahn-Teller effect to enhance structural stability. We gauge a fundamental understanding of the Mg-O and Na-O or Mg-O-Na bonding interactions, noting that the ionicity of the Mg-O bond deshields the electronic cloud of oxygen from Na+ ions. Furthermore, calculations of the Van Vleck distortion modes reveal a relaxation of NiO6 octahedra from Jahn-Teller distortion and a reduced electron density at the interlayer with Mg2+ substitution. Long-range (operando X-ray diffraction) and short-range (magic angle spinning nuclear magnetic resonance) structural analyses provide insights into reduced ordering, allowing a stable continuous solid solution. Overall, Mg-substitution results in a high-capacity retention of ~96 % even after 100 cycles, showcasing the potential of this strategy for overcoming the structural instabilities and enhancing the performance of sodium-ion batteries.

Mitigating Sodium Ordering for Enhanced Solid Solution Behavior in Layered NaNiO2 Cathodes

AbstractThe O‐type layered nickel oxides suffer from undesired cooperative Jahn–Teller distortion stemming from Ni3+ ions and undergo multiple biphasic structural transformations during the insertion/extraction of large Na+ ions, posing a significant challenge to stabilize the structural integrity. We present here a systematic investigation of the impact of substituting 5 % divalent (Mg2+) or trivalent (Al3+ or Co3+) ions for Ni3+ to alleviate Na+ion ordering and perturb the Jahn–Teller effect to enhance structural stability. We gauge a fundamental understanding of the Mg−O and Na−O or Mg−O−Na bonding interactions, noting that the ionicity of the Mg−O bond deshields the electronic cloud of oxygen from Na+ ions. Furthermore, calculations of the Van Vleck distortion modes reveal a relaxation of NiO6 octahedra from Jahn–Teller distortion and a reduced electron density at the interlayer with Mg2+ substitution. Long‐range (operandoX‐ray diffraction) and short‐range (magic angle spinning nuclear magnetic resonance) structural analyses provide insights into reduced ordering, allowing a stable continuous solid solution. Overall, Mg‐substitution results in a high‐capacity retention of ~96 % even after 100 cycles, showcasing the potential of this strategy for overcoming the structural instabilities and enhancing the performance of sodium‐ion batteries.