Solid-state Nuclear Magnetic Resonance Techniques Research Articles

Ion-conducting glass-ceramics for energy-storage applications

Abstract

Composition and structure of natural organic matter through advanced nuclear magnetic resonance techniques

Natural organic matter (NOM) plays important roles in biological, chemical, and physical processes within the terrestrial and aquatic ecosystem. Despite its importance, a clear and exhaustive knowledge on NOM chemistry still lacks. Aiming to prove that advanced solid-state 13C nuclear magnetic resonance (NMR) techniques may contribute to fill such a gap, in this paper we reported relevant examples of its applicability to NOM components, such as biomass, deposition material, sediments, and kerogen samples. It is found that nonhydrolyzable organic carbons (NHC), chars, and polymethylene carbons are important in the investigated samples. The structure of each of the NHC fractions is similar to that of kerogens, highlighting the importance of selective preservation of NOM to the kerogen origin in the investigated aquatic ecosystems. Moreover, during the artificial maturation experiments of kerogen, the chemical and structural characteristics such as protonated aromatic, nonprotonated carbons, and aromatic cluster size play important roles in the origin and variation of nanoporosity during kerogen maturation.Graphical abstractNMR parameters of thermally stimulated kerogens

Uncovering the Rotation and Translational Mobility of Benzene Confined in UiO-66 (Zr) Metal–Organic Framework by the 2H NMR–QENS Experimental Toolbox

A combination of experimental quasi-elastic neutron scattering (QENS) and deuterium solid-state nuclear magnetic resonance (2H NMR) techniques was used to uncover the molecular mobility of benzene confined in UiO-66 (Zr) MOF with a 3D cage-window-cage type porous network topology. We have shown that tetrahedral and octahedral cages of UiO-66 offer notably different states of confinement for benzene. Below 163 K, the guest molecules of benzene are represented by two different dynamic states: in the smaller (tetrahedral) cage the benzene is able to exhibit only anisotropic C6 rotation and some limited librations. In the octahedral cage, there is enough space for additional C2 axial rotation and the isotropic random reorientation. Rotational motions have been characterized by the rate constants and corresponding activation energies. The two dynamic states merge as the temperature increases due to translational jump diffusion with the limiting step being the passage through the window between the cages. Both ...

N-ethyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide-electrospun polyvinylidene fluoride composite electrolytes: characterization and lithium cell studies.

Using the organic ionic plastic crystal N-ethyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide ([C2mpyr][FSI]) with electrospun nanofibers, LiFSI doped [C2mpyr][FSI]-PVdF composites were developed as solid state, self-standing electrolyte membranes. Different lithium salt concentration were investigated, with 10 mol% LiFSI found to be optimal amongst those assessed. Composites with different weight ratios of plastic crystal and polymer were prepared and 10 wt% polymer gave the highest conductivity. In addition, the effects of PVdF incorporation on the morphological, thermal, and structural properties of the organic ionic plastic crystal were investigated. Ion mobilities were also studied using solid-state nuclear magnetic resonance techniques. The electrolytes were then assembled into lithium symmetric cells and cycled galvanostatically at 0.13 mA cm-2 at both ambient temperature and at 50 °C, for more than 500 cycles.

Chemical Reactions and Their Kinetics of atactic-Polyacrylonitrile As Revealed by Solid-State 13C NMR

Inter- and intramolecular chemical reactions and their kinetics for 13C-labeled atactic-polyacrylonitrile (aPAN) powder heat-treated at 220–290 °C under air and vacuum were investigated by various solid-state nuclear magnetic resonance (ssNMR) techniques. By applying 13C direct polarization magic angle spinning (DPMAS) as well as through-bond and through-space double quantum/single quantum ssNMR techniques, it was concluded that aPAN heat-treated under air at 290 °C for 300 min adopted the ladder formation, namely, conjugated six-membered aromatic rings with partially cross-linked and oxidized rings and polyene components. In contrast, aPAN heat-treated under vacuum at the same condition thermally decomposed into oligomeric chains that were mainly composed of isolated aromatic rings connected by alkyl segments. Furthermore, early stages of the chemical reactions were investigated by 13C cross-polarization (CP) and DPMAS spectra. The latter provided quantitative information regarding the kinetics of the chemical reactions. As a result, it was shown that chemical reactions under oxygen occurred homogeneously with a higher activation energy (Ea) of 122 ± 3 kJ/mol compared to that of vacuum at 47 ± 2 kJ/mol. By comparing both chemical structures and kinetics under two different conditions, the chemical reaction mechanisms of aPAN will be discussed in detail.

Chemical and structural characterization of thermally simulated kerogen and its relationship with microporosity

Kerogen was isolated from the Maoming shale at different temperatures to understand changes in chemical, structural and porosity characteristics during artificial maturation. Advanced solid-state 13C nuclear magnetic resonance (NMR) techniques were employed along with Fourier transform infrared (FT-IR), Raman spectroscopy (RS), stable carbon isotopes, and Rock-Eval pyrolysis to characterize the organic matter (OM), whereas the microporosity and surface properties were elucidated using N2 and CO2 adsorption techniques. As the temperature increased, the aliphatic and carbonyl carbons of the kerogen samples showed remarkable decreases in abundance together with an increase of non-protonated and protonated aromatic carbons. Moreover, the kerogen became more enriched in 13C and had a higher degree of crystallization with increasing Ro and Tmax. The aromaticity ranged from 46.9% to 94.7% and the minimum aromatic cluster size varied from 10 carbons at 350 °C to 38 carbons at 500 °C, which was significantly related to the microporosity (Vo, d-co2) of the kerogen samples and their nonlinear sorption of phenanthrene and benzene. The microporosity was extensively affected by the loss of aliphatic carbon and the increase of aromatic fused carbon. When the temperature reached 500 °C, the collapse of aromatic interlayer remarkably reduced the micropore volume in the kerogen, and then resulted in the decreasing adsorption of hydrophobic organic chemicals (HOCs). The above observation confirms the molecular sieve effect in the kerogen samples. In addition, the micro-filling adsorption for HOCs is dominant on the thermally simulated kerogen samples.

Combining 27Al Solid-State NMR and First-Principles Simulations To Explore Crystal Structure in Disordered Aluminum Oxynitride.

The nuclear magnetic resonance (NMR) technique gives insight into the local information in a crystal structure, while Rietveld refinement of powder X-ray diffraction (PXRD) sketches out the framework of a crystal lattice. In this work, first-principles calculations were combined with the solid-state NMR technique and Rietveld refinement to explore the crystal structure of a disordered aluminum oxynitride (γ-alon). The theoretical NMR parameters (chemical shift, δiso, quadrupolar coupling constants, CQ, and asymmetry parameter, η) of Al22.5O28.5N3.5, predicted by the gauge-including projector augmented wave (GIPAW) algorithm, were used to facilitate the analytical investigation of the 27Al magic-angle spinning (MAS) NMR spectra of the as-prepared sample, whose formula was confirmed to be Al2.811O3.565N0.435 by quantitative analysis. The experimental δiso, CQ, and η of 27Al showed a small discrepancy compared with theoretical models. The ratio of aluminum located at the 8a to 16d sites was calculated to be 0.531 from the relative integration of peaks in the 27Al NMR spectra. The occupancies of aluminum at the 8a and 16d positions were determined through NMR investigations to be 0.9755 and 0.9178, respectively, and were used in the Rietveld refinement to obtain the lattice parameter and anion parameter of Al2.811O3.565N0.435. The results from 27Al NMR investigations and PXRD structural refinement complemented each other. This work provides a powerful and accessible strategy to precisely understand the crystal structure of novel oxynitride materials with multiple disorder.

Molecular origin of the shape memory properties of heat-shrink crosslinked polymers as revealed by solid-state NMR

Understanding the shape memory properties of heat-shrink polymers (HSPs) at the molecular level is crucial for the design and synthesis of advanced HSP materials. Herein, we employed a variety of in situ variable-temperature (VT) solid-state nuclear magnetic resonance (NMR) techniques, in combination with other methods, to investigate the evolution of the individual components of a poly(ethylene-co-vinyl acetate)-based HSP with mobility contrast and segmental orientation during the heat-shrink process. In situ VT 1H T2 relaxometry experiments clearly revealed the presence and evolution of rigid, semi-rigid and mobile components associated with stable crystallites and crosslinkage, less-stable crystallites and the amorphous phase in HSPs with increasing temperature, respectively. In particular, the reversible switching phase should be predominately attributed to the semi-rigid crystalline components, which dramatically decreased after the onset temperature and completely disappeared at the end temperature used in the heat-shrink process. The fixed phase associated with the rigid crosslinkage was observed at high temperatures. Furthermore, the activation energy (Ea) of the mobile components decreased after the heat-shrink process, indicating the chain relaxation of deformed segments in the expanded sample. This was confirmed by Baum−Pines 1H double-quantum experiments, which also revealed an inflection point of the chain mobility at the onset temperature (∼330 K) of the heat-shrink process, at which the restricted mobile chains in the expanded sample are nearly completely relaxed. This imbues HSPs with the ability to shape change. In addition, two-dimensional wide-angle X-ray diffraction (WAXD) indicated that the weak orientation of crystalline domains in HSP disappears after the heat-shrink process. Based on the NMR and WAXD experimental results, a model was proposed to describe the molecular mechanism underlying HSPs' shape memory properties. Finally, proton T2 relaxometry combined with multiple-quantum NMR was confirmed to be a powerful method to study HSPs shape memory properties.

Chemical nature of humic substances in two typical Chinese soils (upland vs paddy soil): A comparative advanced solid state NMR study

Knowledge of the structural features of humic substances (HSs) is essential for elucidating the mechanisms of humification in different soil environments and realizing their profound roles in environmental issues. The aim of this work was to investigate the chemical structures of fulvic acid (FA), humic acid (HA) and humin (HM) fractions isolated from an upland soil (Fluvisol) and a paddy soil (Anthrosol) typical in China using advanced solid-state 13C nuclear magnetic resonance (NMR) techniques. The results revealed that there were great structural differences of HSs between the two soils. The two FAs showed distinct quantitative differences in aliphatics with more polysaccharides in the FA from the upland soil than from the paddy soil. The HM from the upland soil differed from the paddy soil HM in having more proteins/peptides (23% vs 20%), total aromatics (21% vs 12%) as well as fewer lipids (24% vs 35%) and polysaccharides (27% vs 31%). The HM fractions represented the most different components of organic matter between the two soils. The degree of difference between the two HAs fell in between that of FAs and HM fractions. In particular, the HA from the upland soil had relatively greater degree of aromaticity. Our study indicated that the upland soil exhibited a higher degree of humification compared with the paddy soil. Among the three humic fractions, the FAs featured COO/N-CO groups, and the HAs were more enriched in protonated aromatic C for both soils. In contrast, the two HM fractions contained more O-alkyl C and fewer aromatics than did the other humic fractions, being closer to the original organic materials in soils. We speculate that the evolutionary route of HSs is likely to be the transformation of original organic materials into HM, followed by increased degradation, further oxidization and conversion into HA, and then into FA.

The relation of structural mobility and water sorption of soil organic matter studied by 1H and 13C solid-state NMR

The impact of low water contents on the molecular mobility of soil organic matter (SOM) and its most frequent components was investigated. Combined 1H, 2H, and 13C solid-state nuclear magnetic resonance (NMR) techniques allow for an advanced insight into mechanisms of water uptake under defined atmospheres and its effect on SOM segment mobility. The major individual organic components of two peats, a gleyic podsol and a number of model substances (cutin, suberin, wood and cellulose) were distinguished with respect to their contribution to the 1H and 13C NMR spectra. Water molecules and mobile polymer constituents of SOM contribute to the mobile fraction in 1H NMR wide line spectra. Poly(methylene), being most probably part of amphiphilic molecules, have been identified as SOM components that are mobilized in the presence of water. Even though being of hydrophobic nature, water acts as a plasticizer on such long chain aliphatic soil components. Differential scanning calorimetry measurements of SOM samples support this insight in terms of a thermal step transition. Based on our findings, comparison of experimental results from different soils with varying water contents and soil composition should consider mobility effects of both, aliphatic moieties as well as polar moieties of SOM.

Insights into the Effects of Zinc Doping on Structural Phase Transition of P2-Type Sodium Nickel Manganese Oxide Cathodes for High-Energy Sodium Ion Batteries.

P2-type sodium nickel manganese oxide-based cathode materials with higher energy densities are prime candidates for applications in rechargeable sodium ion batteries. A systematic study combining in situ high energy X-ray diffraction (HEXRD), ex situ X-ray absorption fine spectroscopy (XAFS), transmission electron microscopy (TEM), and solid-state nuclear magnetic resonance (SS-NMR) techniques was carried out to gain a deep insight into the structural evolution of P2-Na0.66Ni0.33-xZnxMn0.67O2 (x = 0, 0.07) during cycling. In situ HEXRD and ex situ TEM measurements indicate that an irreversible phase transition occurs upon sodium insertion-extraction of Na0.66Ni0.33Mn0.67O2. Zinc doping of this system results in a high structural reversibility. XAFS measurements indicate that both materials are almost completely dependent on the Ni(4+)/Ni(3+)/Ni(2+) redox couple to provide charge/discharge capacity. SS-NMR measurements indicate that both reversible and irreversible migration of transition metal ions into the sodium layer occurs in the material at the fully charged state. The irreversible migration of transition metal ions triggers a structural distortion, leading to the observed capacity and voltage fading. Our results allow a new understanding of the importance of improving the stability of transition metal layers.

Understanding the Roles of Electrolyte Additives on the Surface Modification Mechanism of Silicon-Based Anodes in Lithium-Ion Batteries

Silicon is considered as a promising candidate of the anode material for the next generation lithium-ion batteries, due to its substantially higher gravimetric and volumetric capacity compared to conventionally used graphite. Electrolyte additives, fluoroethylene carbonate (FEC) and vinylene carbonate (VC) particularly, are usually applied for silicon-based lithium-ion batteries to tackle the problems such as poor capacity retention and low coulombic efficiency.1-3 In the present work, the decomposition mechanism of FEC as well as the surface modification of Si electrodes were investigated.4 It was observed that the FEC additive degrades at a higher reduction potential prior to the other carbonate solvents. A conformal solid electrolyte interphase (SEI), which consists of the decomposition products of FEC, is instantaneously formed on the silicon electrode as a result. This stable SEI layer sufficiently limits the emergence of cracks and suppresses the additional SEI formation from the decomposition of other electrolyte components. Both of these effects lead to a slower increase in polarization, thus a slower capacity fading, for the FEC containing cell. The differences in the SEI layer, formed with or without the presence of FEC, are schematically demonstrated in Fig 1. Besides, it was also observed that the LiPF6 decomposition can be influenced with the presence of FEC, and this was further studied with a combination of X-ray photoelectron spectroscopy (XPS) and solid-state nuclear magnetic resonance (NMR) techniques. We also demonstrated that by forming an effective SEI layer with the FEC and VC electrolyte additives, the silicon electrodes can be equally well functioning with a novel lithium 4,5-dicyano-2-(trifluoromethyl)imidazolide (LiTDI)-based electrolyte as with the state-of-art LiPF6-based electrolyte.5 Figure 1

Compositional-dependent properties of Pr3+-doped multicomponent fluoro-phosphate glasses for visible applications: a photoluminescence study

Five fluoro-phosphate (FP) glasses of different compositions, 49.5P2O5–10AlF3–10BaF2–10SrF2–10PbO–10M (M = Li2O, Na2O, K2O, ZnO, and Bi2O3), doped with 0.5 mol% praseodymium were prepared by melt quenching technique. For these glass matrices, structural, thermal, dielectric, electrical, and optical properties have been studied. The structures are characterized by XRD, Fourier transform infrared, Raman spectroscopy, and solid-state 31P and 27Al magic angle spinning nuclear magnetic resonance techniques. The chemical and electronic states of these glass materials are characterized by X-ray photoelectron spectroscopy. The thermal stability for the host glass matrix is estimated from differential scanning calorimetry technique. From the impedance spectroscopy, various parameters, viz. electrical conductivity, dielectric constant (e′), and dielectric losses (tan δ), at various frequencies and temperatures have been measured. X-ray absorption near-edge spectroscopy was used to study the electronic structure of praseodymium in the host glass matrices. By analyzing the absorption spectra with Judd–Ofelt theory, three intensity parameters (Ω λ , λ = 2, 4, 6) are obtained. In turn, these parameters are used to calculate radiative properties such as emission probabilities (A R), radiative lifetimes (τ R), and integrated absorption cross sections (Σ) of different Pr3+ transitions. Luminescence parameters such as stimulated emission cross sections (σ p) and branching ratios (β exp) have been studied through photoluminescence spectra. Further, decay time constants are estimated from the decay profiles of Pr3+-doped different FP glasses.

A view of pathogenic fibrils

Parkinson's Disease The protein α-synuclein (α-syn) accumulates in the brains of people with Parkinson's disease (PD), forming fibrils that are a hallmark of the disease. Tuttle et al. used sophisticated solid-state nuclear magnetic resonance techniques to determine a high-resolution three-dimensional structure of α-syn fibrils which they validated by electron microscopy and x-ray fiber diffraction. The structure exhibits many of the features that stabilize typical amyloid fibrils (like those seen in Alzheimer's disease), including a stacked α-sheet structure with a tightly packed core, but in this case the strands in each α sheet follow a serpentine, Greek-key–like pattern. The structure may facilitate the development of diagnostic agents for PD. Nat. Struct. Mol. Biol. 10.1038/nsmb.3194 (2016).

Solid-State NMR Investigations on the Structure and Dynamics of the Ionic Conductor Li1+xAlxTi2–x(PO4)3 (0.0 ≤ x ≤ 1.0)

The local structure and mobility of lithium ions of the NASICON-type ionic conductor Li1+xAlxTi2–x(PO4)3 (with x = 0.0, 0.1, 0.2, 0.35, 0.5, 0.7 and 1.0), synthesized using conventional solid-state reaction route have been studied with solid-state nuclear magnetic resonance (NMR) techniques. 6Li, 7Li, 27Al, and 31P solid-state NMR experiments have been employed to trace the structural changes with varying cation concentration. The structural evolution and the creation of new Al and P environments with changing cation contents were studied by magic-angle spinning (MAS) NMR measurements. 6Li MAS NMR and 27Al triple-quantum MAS (3QMAS) show high-resolution spectra enabling site assignments and phase-purity inspections. The temperature dependences of 7Li NMR spin–lattice relaxation (SLR) rates for different compositions yield important information on the lithium ion mobility in the systems. Li ion jump rates, the activation energies, and the dimensionality of Li diffusion were deduced from the SLR experiments...

Solid-State NMR Characterization of Mixed Phosphonic Acid Ligand Binding and Organization on Silica Nanoparticles.

As ligand functionalization of nanomaterials becomes more complex, methods to characterize the organization of multiple ligands on surfaces is required. In an effort to further the understanding of ligand-surface interactions, a combination of multinuclear ((1)H, (29)Si, (31)P) and multidimensional solid-state nuclear magnetic resonance (NMR) techniques was utilized to characterize the phosphonic acid functionalization of fumed silica nanoparticles using methylphosphonic acid (MPA) and phenylphosphonic acid (PPA). (1)H → (29)Si cross-polarization (CP)-magic angle spinning (MAS) solid-state NMR was used to selectively detect silicon atoms near hydrogen atoms (primarily surface species); these results indicate that geminal silanols are preferentially depleted during the functionalization with phosphonic acids. (1)H → (31)P CP-MAS solid-state NMR measurements on the functionalized silica nanoparticles show three distinct resonances shifted upfield (lower ppm) and broadened compared to the resonances of the crystalline ligands. Quantitative (31)P MAS solid-state NMR measurements indicate that ligands favor a monodentate binding mode. When fumed silica nanoparticles were functionalized with an equal molar ratio of MPA and PPA, the MPA bound the nanoparticle surface preferentially. Cross-peaks apparent in the 2D (1)H exchange spectroscopy (EXSY) NMR measurements of the multiligand sample at short mixing times indicate that the MPA and PPA are spatially close (≤5 Å) on the surface of the nanostructure. Furthermore, (1)H-(1)H double quantum-single quantum (DQ-SQ) back-to-back (BABA) 2D NMR spectra further confirmed that MPA and PPA are strongly dipolar coupled with observation of DQ intermolecular contacts between the ligands. DQ experimental buildup curves and simulations indicate that the average distance between MPA and PPA is no further than 4.2 ± 0.2 Å.

Application of solid-state NMR spectroscopy to evaluate cassava genotypes

Cassava is widely cultivated in tropical and subtropical regions of Africa, Asia and Latin America and is the third most important source of calories in the tropics, after rice and maize. Cassava is mainly composed of starch, fibre, proteins, lipids and essential minerals. However, the nutrient composition differs according to the variety. Despite the large number of cassava genotypes, studies involving both chemical composition and structural aspects through molecular dynamic behaviour are scarce. The present study investigated six cassava genotypes with respect to chemical composition and molecular dynamic behaviour, employing nuclear magnetic resonance (NMR) spectroscopy. The samples were characterized by high-field NMR and low-field NMR techniques, namely cross-polarization magic-angle spinning, variable contact time, proton spin-lattice relaxation time in rotating frame, spin-spin relaxation time and NMR measurements of lipid fraction. The combined use of solid-state NMR techniques was shown to be a powerful tool for characterizing foods such as cassava. The main results revealed that the six cassava genotypes differ in the chemical composition of the starch, as well as the minor components, such as fibre and oil. These differences influence structural aspects; thus changes in the molecular dynamic behaviour can be observed.

Modern solid state NMR techniques and concepts in structural studies of synthetic polymers

In this mini-review, we present the solid state nuclear magnetic resonance (NMR) methods which trace the new tendency in structural studies of synthetic polymers. The review is organized into three sections. In the first part, short theoretical background and introduction to very fast magic angle spinning NMR technique with sample rotation 60 kHz are shown. The second part presents method for enhancing the sensitivity of NMR experiments by application of dynamic nuclear polarization magic angle spinning technique. In the third section, the power of the NMR crystallography approach which can be used for fine refinement of polymers structure on the atomic level is discussed. Copyright © 2016 John Wiley & Sons, Ltd.

Two-Dimensional Correlation of Isotropic and Directional Diffusion Using NMR.

Diffusion nuclear magnetic resonance (NMR) is a powerful technique for studying porous media, but yields ambiguous results when the sample comprises multiple regions with different pore sizes, shapes, and orientations. Inspired by solid-state NMR techniques for correlating isotropic and anisotropic chemical shifts, we propose a diffusion NMR method to resolve said ambiguity. Numerical data inversion relies on sparse representation of the data in a basis of radial and axial diffusivities. Experiments are performed on a composite sample with a cell suspension and a liquid crystal.

Application of Solid-State NMR Relaxometry for Characterization and Formulation Optimization of Grinding-Induced Drug Nanoparticle.

The formation mechanism of drug nanoparticles was investigated using solid-state nuclear magnetic resonance (NMR) techniques for the efficient discovery of an optimized nanoparticle formulation. The cogrinding of nifedipine (NIF) with polymers, including hydroxypropyl methylcellulose (HPMC) and polyvinylpyrrolidone (PVP), and sodium dodecyl sulfate (SDS) was performed to prepare the NIF nanoparticle formulations. Then, solid-state NMR relaxometry was used for the nanometer-order characterization of NIF in the polymer matrix. Solid-state NMR measurements revealed that the crystal size of NIF was reduced to several tens of nanometers with amorphization of NIF by cogrinding with HPMC and SDS for 100 min. Similarly, the size of the NIF crystal was reduced to less than 90 nm in the 40 min ground mixture of NIF/PVP/SDS. Furthermore, 100 min grinding of NIF/PVP/SDS induced amorphization of almost all the NIF crystals followed by nanosizing. The hydrogen bond between NIF and PVP led to the efficient amorphization of NIF in the NIF/PVP/SDS system compared with NIF/HPMC/SDS system. The efficient nanosizing of the NIF crystal in the solid state, revealed by the solid-state NMR relaxation time measurements, enabled the formation of large amounts of NIF nanoparticles in water followed by the polymer dissolution. In contrast, excess amorphization of the NIF crystals failed to efficiently prepare the NIF nanoparticles. The solid-state characterization of the crystalline NIF revealed good correlation with the NIF nanoparticles formation during aqueous dispersion. Furthermore, the solid-state NMR measurements including relaxometry successfully elucidated the nanometer-order dispersion state of NIF in polymer matrix, leading to the discovery of optimized conditions for the preparation of suitable drug nanoparticles.