Magic Angle Spinning Nuclear Magnetic Resonance Spectroscopy Research Articles

Evidence for new fluoride coordination in SiO2-Al2O3-P2O5-CaO/SrO-CaF2 compositions used in ion-leachable ionomer-type cements: A 19F MAS-NMR investigation

Glass ionomer-type glasses are widely utilized in industrial and biomaterial applications due to their unique combination of biocompatibility, strong adhesive properties, and controlled ion release. The structural understanding of fluoride ions in these materials is critical for optimizing their performance and tailoring their properties to specific applications. In this study, we employ solid-state 19F magic-angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopy as a powerful tool to investigate the fluoride coordination environments in glass-ionomer-type glasses. A series of strontium-substituted glasses in the system SiO2-Al2O3-P2O5-CaO/SrO-CaF2 were synthesised by the high-temperature melt-quench technique and analysed by 19F MAS-NMR spectroscopy. A previously unknown F coordination environment with Sr was discovered.

Effect of precursor morphology of cellulose-based hard carbon anodes for sodium-ion batteries

Hard carbon with different microstructures and physicochemical properties can be obtained based on the precursor used, and these properties have a direct impact on the electrochemical performance. Herein, two different precursors from a single source of waste cotton textiles have been prepared to be either cotton snippets retaining the original fiber structure of cotton or a microfibrillated cellulose, which has a very different morphology and surface area. Both the cotton snippet (CS) and the microfibrillated cellulose (MFC) have been carbonized to prepare hard carbons MFC-C and CS-C, and their electrochemical performance is evaluated in sodium-ion batteries (NIBs). Physicochemical properties in terms of a higher interlayer spacing of 3.71 Å and a high defect ratio (ID/IG) of 1.10 resulted in CS-C having a relatively higher specific capacity of 240 mAh g-1 in comparison to 199 mAh g-1 in MFC-C when cycled at 50 mA g-1. In addition, ex-situ MAS (magic angle spinning) NMR (nuclear magnetic resonance) spectroscopy on the solid electrolyte interphase (SEI) layer of CS-C revealed a lesser amount of conductive SEI layer on its surface compared to MFC-C, mainly composed of NaF and an additional FSI-derived Na complex, suggested to be Na2 [SO3-N-SO2F]). In contrast, MFC-C revealed a greater amount of SEI-related compounds, which is interpreted as a thicker SEI layer resulting in a long Na+ diffusion pathway and slower Na+ reaction kinetics. This study provides insight into the effect of microstructural differences arising from different cellulose precursors on the electrochemical performance, thereby aiding in the fabrication and optimization of hard carbon anodes for sodium-ion batteries.

Molecular Profiling of Peanut under Raw, Roasting, and Autoclaving Conditions Using High-Resolution Magic Angle Spinning and Solution 1H NMR Spectroscopy.

Higher rates of peanut allergy have been observed in countries that commonly roast peanuts prior to consumption. Despite the importance of understanding the role of thermal processing in allergy and on peanut composition, studies toward generating signatures that identify molecular contents following processing are scant. Here, we identified spectral signatures to track changes and differences in the molecular composition of peanuts under raw, roasted, and high-pressure and high-temperature autoclaved conditions. We analyzed both the solid flesh of the seed and solutions derived from soaking peanuts using High-Resolution Magic Angle Spinning (HR-MAS) and solution 1H Nuclear Magnetic Resonance (NMR) spectroscopy, respectively. The NMR spectra of intact peanuts revealed triglycerides as the dominant species, assigned on the basis of multiplets at 4.1 and 4.3 ppm, and corresponding defatted flours revealed the presence of sugars. Sucrose assigned based on a doublet at 5.4 ppm (anomeric proton), and triglycerides were the most abundant small molecules observed, with little variation between conditions. Soaked peanut solutions were devoid of lipids, and their resulting spectra matched the profiles of defatted peanuts. Spectral signatures resulting from autoclaving differed strikingly between those from raw and roasted peanuts, with considerable line-broadening in regions corresponding to proteins and amino-acid side chains, from 0.5 to 2.0 ppm and 6.5 to 8.5 ppm. Taken together, by using complementary NMR methods to obtain a fingerprint of the molecular components in peanuts, we demonstrated that autoclaving led to a distinct composition, likely resulting from the hydrolytic cleavage of proteins, the most important molecule of the allergic reaction.

Conversion of N-Acetylglucosamine to 3-Acetamido-5-Acetylfuran over Al-Exchanged Montmorillonite.

3-Acetamido-5-acetylfuran (3A5AF) is a potential platform compound for the production of nitrogen-containing pharmaceuticals and chemicals. 3A5AF can be obtained by dehydration of chitin or its monomer, N-acetylglucosamine (NAG). Here, we examined the use of solid catalysts for the dehydration of NAG to 3A5AF to achieve a more economical process that uses a recyclable catalyst. NAG was dehydrated using various solid catalysts in the presence of NaCl and N,N-dimethyl acetamide as solvent at 433 K. The yield of 3A5AF with the solid catalysts decreased in the following order: Al-exchanged montmorillonite>H-ZSM-5 (SiO2 /Al2 O3 =40)>H-montmorillonite (K-10)>Amberlyst15>H-ZSM-5 (SiO2 /Al2 O3 =300)>TiO2 >γ-Al2 O3 >ZrO2 >SiO2 ⋅ MgO>Na-montmorillonite. The highest yield of 3A5AF (14 %) was obtained with the Al-exchanged montmorillonite. The montmorillonite catalysts were characterized by using inductively coupled plasma optical emission spectroscopy, energy-dispersive X-ray spectroscopy, N2 adsorption, Fourier-transformed infrared spectroscopy, X-ray diffraction, and 27 Al magic-angle spinning nuclear magnetic resonance spectroscopy (MAS-NMR). In addition, a combined catalyst of Al-exchanged montmorillonite and Cl- from synthetic hydrotalcite was found to be an active and recyclable solid catalyst for NAG dehydration to 3A5AF.

Disorder and Oxide Ion Diffusion Mechanism in La1.54Sr0.46Ga3O7.27 Melilite from Nuclear Magnetic Resonance.

Layered tetrahedral network melilite is a promising structural family of fast ion conductors that exhibits the flexibility required to accommodate interstitial oxide anions, leading to excellent ionic transport properties at moderate temperatures. Here, we present a combined experimental and computational magic angle spinning (MAS) nuclear magnetic resonance (NMR) approach which aims at elucidating the local configurational disorder and oxide ion diffusion mechanism in a key member of this structural family possessing the La1.54Sr0.46Ga3O7.27 composition. 17O and 71Ga MAS NMR spectra display complex spectral line shapes that could be accurately predicted using a computational ensemble-based approach to model site disorder across multiple cationic and anionic sites, thereby enabling the assignment of bridging/nonbridging oxygens and the identification of distinct gallium coordination environments. The 17O and 71Ga MAS NMR spectra of La1.54Sr0.46Ga3O7.27 display additional features not observed for the parent LaSrGa3O7 phase which are attributed to interstitial oxide ions incorporated upon cation doping and stabilized by the formation of five-coordinate Ga centers conferring framework flexibility. 17O high-temperature (HT) MAS NMR experiments capture exchange within the bridging oxygens at 130 °C and reveal coalescence of all oxygen signals in La1.54Sr0.46Ga3O7.27 at approximately 300 °C, indicative of the participation of both interstitial and framework oxide ions in the transport process. These results further supported by the coalescence of the 71Ga resonances in the 71Ga HT MAS NMR spectra of La1.54Sr0.46Ga3O7.27 unequivocally provide evidence of the conduction mechanism in this melilite phase and highlight the potential of MAS NMR spectroscopy to enhance the understanding of ionic motion in solid electrolytes.

Solid-state NMR spectroscopy at ultrahigh resolution for structural and dynamical studies of MOFs

To characterize the structure and dynamics of metal–-organic frameworks (MOFs) in-depth at the molecular level, it is necessary to pursue high-resolution solid-state magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. Spectral resolution is usually affected by the quality of materials and various experimental conditions, of which magic angle (MA) accuracy is a crucial determinant. The current industrial criteria for MA calibration based on the common standard of KBr were found insufficient in guaranteeing optimal resolution MAS NMR for highly ordered MOFs. To drive towards higher-resolution MAS NMR spectroscopy, we propose a calibration protocol for more accurate MA with a higher-precision criterion based on 79Br MAS NMR of KBr, where the linewidth ratio of the fifth-order spinning sideband to the central band of KBr should be less than 1.00. As a result, ultrahigh-resolution 13C cross-polarization (CP) MAS NMR of MOF-5 is achieved with minimal linewidths as low as 4 Hz, and therefore MOF-5 can be used as a new standard convenient for verifying MA accuracy and also optimizing 13C CP conditions. Maintaining high-precision MA under variable temperature (VT) was found challenging on certain commercial MAS NMR probes, as was systematically investigated by VT NMR using KBr and MOF-5. Nevertheless, ultrahigh-resolution MAS NMR spectroscopy with stable MA under VT is employed to reveal fine structures and linker dynamics of a series of Zn-based MOFs with highly regulated structures. The ultrahigh-resolution NMR methodcan be generally applied to study a broad range of MOFs and other materials.

Aluminosilicate-Supported Catalysts for the Synthesis of Cyclic Carbonates by Reaction of CO2 with the Corresponding Epoxides.

Functionalized aluminosilicate materials were studied as catalysts for the conversion of different cyclic carbonates to the corresponding epoxides by the addition of CO2. Aluminum was incorporated in the mesostructured SBA-15 silica network. Thereafter, functionalization with imidazolium chloride or magnesium oxide was performed on the Al_SBA-15 supports. The isomorphic substitution of Si with Al and the resulting acidity of the supports were investigated via 27Al magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy and NH3 adsorption microcalorimetry. The Al content and the amount of MgO were quantified via inductively coupled plasma optical emission spectroscopy (ICP-OES) analysis. The anchoring of the imidazolium salt was assessed by 29Si and 13C MAS NMR spectroscopy and quantified by combustion chemical analysis. Textural and structural properties of supports and catalysts were studied by N2 physisorption and X-ray diffraction (XRD). The functionalized systems were then tested as catalysts for the conversion of CO2 and epoxides to cyclic carbonates in a batch reactor at 100 or 125 °C, with an initial CO2 pressure (at room temperature) of 25 bar. Whereas the activity of the MgO/xAl_SBA-15 systems was moderate for the conversion of glycidol to the corresponding cyclic carbonate, the Al_SBA-15-supported imidazolium chloride catalysts gave excellent results over different epoxides (conversion of glycidol, epichlorohydrin, and styrene oxide up to 89%, 78%, and 18%, respectively). Reusability tests were also performed. Even when some deactivation from one run to the other was observed, a comparison with the literature showed the Al-containing imidazolium systems to be promising catalysts. The fully heterogeneous nature of the present catalysts, where the inorganic support on which the imidazolium species are immobilized also contains the Lewis acid sites, gives them a further advantage with respect to most of the catalytic systems reported in the literature so far.

Crystallographic and Physicochemical Analysis of Bovine and Human Teeth Using X-ray Diffraction and Solid-State Nuclear Magnetic Resonance.

Dental research often uses bovine teeth as a substitute for human teeth. The aim of this study was to evaluate differences in the crystalline nanostructures of enamel and dentin between bovine and human teeth, using X-ray diffraction (XRD) and solid-state nuclear magnetic resonance (NMR). The crystallite size (crystallinity) and microstrains were analyzed using XRD with the Rietveld refinement technique and the Halder-Wagner method. The 31P and 1H NMR chemical environments were analyzed by two-dimensional (2D) 1H-31P heteronuclear-correlation (HETCOR) magic-angle spinning (MAS) NMR spectroscopy. Enamel had a greater crystallite size and fewer microstrains than dentin for both bovine and human teeth. When compared between the species, the bovine apatite had a smaller crystallite size with more microstrains than the human apatite for both dentin and enamel. The 2D HETCOR spectra demonstrated that a water-rich layer and inorganic HPO4- ions were abundant in dentin; meanwhile, the hydroxyl group in the lattice site was more dominant in enamel. A greater intensity of the hydroxyl group was detected in human than in bovine for both dentin and enamel. For 31P projections, bovine dentin and bovine enamel have wider linewidths than human dentin and human enamel, respectively. There are differences in the crystallite profile between human and bovine. The results of dental research should be interpreted with caution when bovine teeth are substituted for human teeth.

Correlation of structure and ionic-conductivity in phosphate glass using MAS-NMR and impedance spectroscopy: Influence of sodium salt

In the process of diminishing the safety concerns of sodium-ion batteries, the development of glass-based solid electrolyte materials has received adequate interest. Nevertheless, achieving a high ionic-conductivity at room temperature for glass materials remains a challenging task because of the poor correlation between the conductivity and the glass structure. Here, we attempt to understand the effective influence of NaCl on the structure and ionic-conductivity of the phosphate-based glass network. For this study, $x\mathrm{NaCl}\text{\ensuremath{-}}(100\text{\ensuremath{-}}x$) ($31.725\phantom{\rule{4pt}{0ex}}{\mathrm{Na}}_{2}\mathrm{O}\text{\ensuremath{-}}12.69\phantom{\rule{0.16em}{0ex}}{\mathrm{Al}}_{2}{\mathrm{O}}_{3}\text{\ensuremath{-}}31.725\phantom{\rule{0.16em}{0ex}}{\mathrm{P}}_{2}{\mathrm{O}}_{5}\text{\ensuremath{-}}8.46\phantom{\rule{0.16em}{0ex}}\mathrm{NaF}\text{\ensuremath{-}}5.40\phantom{\rule{0.16em}{0ex}}{\mathrm{Na}}_{2}{\mathrm{SO}}_{4}\text{\ensuremath{-}}10\phantom{\rule{0.16em}{0ex}}{\mathrm{MoO}}_{3}$) glass systems (mol %) were selected, where $x=0$, 5, 10, 15, and 20 mol %. To investigate structural changes with the addition of different NaCl concentrations, $^{27}\mathrm{Al}, ^{23}\mathrm{Na}, ^{31}\mathrm{P}$ magic angle spinning nuclear magnetic resonance (MAS-NMR), $^{31}\mathrm{P}$ two-dimensional (2D) phase-adjusted spinning sideband (PASS), and $^{31}\mathrm{P}$ 2D J-resolved NMR techniques and Raman spectroscopic techniques were utilized. Impedance spectroscopy and ac conductivity spectra were used to assess ionic-conductivity and sodium-ion dynamics, respectively. Impedance spectral analysis reveals that the ionic-conductivity of the base glass is increased by 2.4 times (from 1.85 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}7}$ to 4.44 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}7}$ S/cm at 373 K) with the addition of 20 mol % of NaCl. Raman spectra confirm the presence of P\ensuremath{-}O\ensuremath{-}Mo and the absence of Mo\ensuremath{-}O\ensuremath{-}Mo bonds in these glass systems, and $^{31}\mathrm{P}$ 2D J-resolved spectra indicate the absence of P\ensuremath{-}O\ensuremath{-}P bonds. Upon increasing the NaCl concentration, significant changes in the shapes of $^{31}\mathrm{P}$ and $^{27}\mathrm{Al}$ MAS-NMR spectra were observed, indicating the effective influence of NaCl on the distribution of alumina and phosphorus structural units. Irrespective of the temperature, sodium-ion dynamic studies show that the mean-square displacement $\ensuremath{\langle}{R}^{2}({t}_{p})\ensuremath{\rangle}$ decreases with increasing NaCl concentration up to 10 mol % and then increases with a further increase in NaCl concentration. This investigation aids in understanding the sodium-ion dynamics and the structural information of a multicomponent glass system to enhance the room-temperature conductivity.

A High-Entropy Multicationic Substituted Lithium Argyrodite Superionic Solid Electrolyte

Bulk-type solid-state batteries (SSBs) constitute a promising next-generation technology for electrochemical energy storage. However, in order for SSBs to become competitive with mature battery technologies, (electro)chemically stable, superionic solid electrolytes are much needed. Multicomponent or high-entropy lithium argyrodites have recently attracted attention for their favorable material characteristics. In the present work, we report on increasing the configurational entropy of the Li6+aP1–xMxS5I solid electrolyte system and examine how this affects the structure-conductivity/stability relationships. Using electrochemical impedance spectroscopy and 7Li pulsed field gradient nuclear magnetic resonance (NMR) spectroscopy, multicationic substitution is demonstrated to result in a very low activation energy for Li diffusion of ∼0.2 eV and a high room-temperature ionic conductivity of ∼13 mS cm–1 (for Li6.5[P0.25Si0.25Ge0.25Sb0.25]S5I). The transport properties are rationalized from a structural perspective by means of complementary neutron powder diffraction and magic-angle spinning NMR spectroscopy measurements. The Li6.5[P0.25Si0.25Ge0.25Sb0.25]S5I solid electrolyte was also tested in high-loading SSB cells with a Ni-rich layered oxide cathode and found by X-ray photoelectron spectroscopy to suffer from interfacial side reactions during cycling. Overall, the results of this study indicate that optimization of conductivity is equally important to optimization of stability, and compositionally complex lithium argyrodites represent a new playground for a rational design of (potentially advanced) superionic solid electrolytes.

Exploring the structure of pure germanophospate glasses with different concentrations probed by magic angle spinning NMR spectroscopy.

Phosphate-based glasses such as pure germanophosphate can be achieved at moderately low temperature by means of affordable chemical substances. Nowadays, they become more stimulating because they can be easily doped with alkali, transition metal ions, and rare earth oxides to afford the anticipated physical and/or chemical features for nanoscience applications. Herein, we report an experimental study dealing with the structure of pure germanophosphate glass samples of prepared with different concentrations ranging from 20 up to 70 mole%. 31 P magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy has been employed to characterize the co-formed glasses by two different glass-forming oxides. The components of the phosphate species ( ) in each sample were determined by analyzing the MAS NMR spectra. Interestingly, 31 P MAS NMR spectrum for each sample was found to be characteristic powder patterns of the middle units Q2 . Q2 unit found herein has one oxygen atom bonded towards one germanium atom (non-bridging) and the other two oxygens are bonding towards two phosphorus atoms (bridging) of phosphate group (PO4 ). The results show that Q2 split into two units, Q2 I and Q2 II, due to different shielding of the phosphorus nucleus provided by the next nearest neighbor atoms. The chemical shift is interpreted in terms of the structure of each building unit of the phosphate group. The results obtained herein shed light on the way how to explore the revealed structure of the prepared glasses for the development of supported catalysts. Indeed, owing to their high chemical/thermal stability, the co-formed germanophosphate glasses obtained may prove as useful substrates for potential nanocatalysts.

Structural and physico-mechanical investigations of Na₂B₄O7 geopolymer for γ-radiation attenuating applications

The impact of borax additive on the gamma radiation attenuating property of Geopolymer (GP) systems is presented in this study. Comparative study of control GP and borax blended GP after gamma irradiation is carried out in a Sodium Iodide (NaI) gamma-ray spectrometer. The results indicate a significant increase in linear attenuation coefficient (μ) by 23.4%. The relationship of molecular structure of a material to its radiation attenuation property is crucial to understand for further improving radiation shielding abilities with negligible variation in density or mass of the material. Therefore, the microstructures of the two systems after irradiation were analysed using X-ray Diffractometer (XRD), Thermogravimetric Analysis (TGA), Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), Magic Angle Spinning Nuclear Magnetic Resonance Spectroscopy (MAS-NMR) and Raman spectroscopy. Raman active modes confirms formation of higher order polymer networks in B1g internal mode of Si–O after addition of borax. Solid state 29Si MAS-NMR spectrum of borax blended GP system indicate an enhanced resonance in the Q3 and Q4 region implying the formation of Q3 sheets and Q4 framework, thus indicating the increase in reactivity and polymerisation process after addition of borax. Finally, correlations are drawn between the systems’ microstructural morphology and the corresponding radiation attenuating property.

Metabolomic analysis of endometrial cancer by high-resolution magic angle spinning NMR spectroscopy.

To analyze endometrial metabolite profiles between patients with endometrial cancer and controls. Seventeen (17) women with endometrium cancer and 18 controls were enrolled in this study. 1H HR-MAS (High Resolution-Magic Angle Spinning) NMR (Nuclear Magnetic Resonance) spectroscopy data obtained from endometrial tissue samples of patients with endometrial cancer and control group were analyzed with bioinformatics methods. Principal component analysis (PCA) and the partial least squares discriminant analysis (PLS-DA) score plots obtained with the multivariate statistical analysis of pre-processed spectral data shows a separation between the samples from patients with endometrial cancer and controls. Analysis results suggest that the levels of lactate, glucose, o-phosphoethanolamine, choline, glycerophosphocholine, phosphocholine, leucine, isoleucine, valine, glutamate, glutamine, n-acetyltyrosine, methionine, taurine, alanine, aspartate and phenylalanine are increased in patients with endometrial cancer compared to the controls. The metabolomics signature of patients with endometrial cancer is different from that of benign endometrial tissue.

Activator Anion Influences the Nanostructure of Alkali-Activated Slag Cements

Alkali-activated materials are promising low-carbon alternatives to Portland cement; however, there remains an absence of a fundamental understanding of the effect of different activator types on their reaction products at the atomic scale. Solid-state 27Al and 29Si magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy and 1H–29Si cross-polarization MAS NMR spectroscopy are used to reveal the effect of the activator anion on the nanostructure, cross-linking, and local hydration of aged alkali-activated slag cements. The main reaction product identified is a mixed cross-linked/non-cross-linked sodium-substituted calcium aluminosilicate hydrate (C–(N)–A–S–H) gel with a structure comparable to tobermorite 11 Å. Analysis of cross-polarization kinetics revealed that a higher content of soluble silicate in the activator promoted the incorporation of Al into the aluminosilicate chains of C–(N)–A–S–H gels, charge-balanced preferentially by protons within the gel interlayer. In sodium carbonate-activated slag cements, aluminosilicate chains of C–(N)–A–S–H gels are instead charge-balanced preferentially by Ca2+ or AlV ions. Hydrotalcite was observed as a secondary reaction product independent of the activator used and in higher quantities as the content of sodium carbonate in the activator increases. The presence of soluble silicates in the activator promotes the formation of an Al-rich sodium aluminosilicate hydrate (N–A–S–H) gel which was not identified when using sodium carbonate as the activator. These results demonstrate that the anion type in the activator promotes significant differences in the nanostructure and local hydration of the main binding phases forming in alkali-activated slag cements. This explains the significant differences in properties identified when using these different activators.

Rice hush ash as supplementary cementitious material for calcium aluminate cement – Effects on strength and hydration

Replacing part of calcium aluminate cement (CAC) with reactive rice husk ash (RHA) can directly reduce the impact of rice husk disposal on environment and lower the CO2 footprint of cement. RHA is comparable in chemical composition to silica fume, and thus has the potential to similarly improve the hydration of CAC. In the present study the development of strength and hydration of CAC with various amount of RHA was investigated. By means of calorimetry, X-ray diffraction analysis, 27Al magic-angle spinning-nuclear magnetic resonance spectroscopy, mercury intrusion porosimeter (MIP) and high-resolution scanning electron microscopy (SEM), a detailed insight on the changes of CAC hydration by addition of RHA is gained. Results indicate that RHA does not only accelerate hydration but also improve the early strength of CAC. A high dosage (60%) of RHA densifies the microstructure locally, but the dilution effect induces the decrease of strength. The formed hydrates are C-A-S-H phases with smaller size than CAH and thus a refined pore size develops. Considering the effect of RHA on strength, the amount of substitution should be less than 40%.

Cs absorption capacity and selectivity of crystalline and amorphous Hf and Zr phosphates

Removal of radioactive Cs from sodium-rich solutions is a technical challenge that goes back to post World War II nuclear waste storage and treatment; and interest in this topic was reinvigorated by the Fukushima-Daiichi nuclear power plant disaster, 10 years ago. Since the 1960′s there has been considerable focus on layered Zr phosphates as robust inorganic sorbents for separation of radionuclides such as Cs. Here we present synthesis and characterization, and direct comparison of Cs sorption capacity and selectivity of four related materials: 1) crystalline α-Zr phosphate and α-Hf phosphate, and 2) amorphous analogues of these. Powder X-ray diffraction, thermogravimetry, solid-state 31P magic angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopy, and compositional analysis (inductively coupled plasma optical emission spectroscopy and mass spectroscopy, ICP OES and ICP MS) provided formulae; respectively M(HPO4)2⋅1H2O and M(HPO4)2⋅4H2O (M = Hf, Zr) for crystalline and amorphous analogues. Maximum Cs loading, competitive Cs-Na selectivity and maximum Cs-Na loading followed by the above characterizations plus 133Cs MAS-NMR spectroscopy revealed that amorphous analogues are considerably better Cs-sorbents (based on maximum Cs-loading and selectivity over Na) than the well-studied crystalline Zr-analogue. Additionally, crystalline α-Hf phosphate is better Cs-sorbent than crystalline α-Zr phosphate. All these studies consistently show that Hf phosphate is less crystallize than Zr phosphate, when obtained under similar or identical synthesis conditions. We attribute this to lower solubility of Hf phosphate compared to Zr phosphate, preventing ‘defect healing’ during the synthesis process.

Polymer Networks Synthesized from Poly(Sorbitol Adipate) and Functionalized Poly(Ethylene Glycol).

Polymer networks were prepared by Steglich esterification using poly(sorbitol adipate) (PSA) and poly(sorbitol adipate)-graft-poly(ethylene glycol) mono methyl ether (PSA-g-mPEG12) copolymer. Utilizing multi-hydroxyl functionalities of PSA, poly(ethylene glycol) (PEG) was first grafted onto a PSA backbone. Then the cross-linking of PSA or PSA-g-mPEG12 was carried out with disuccinyl PEG of different molar masses (Suc-PEGn-Suc). Polymers were characterized through nuclear magnetic resonance (NMR) spectroscopy, gel permeation chromatography (GPC), and differential scanning calorimetry (DSC). The degree of swelling of networks was investigated through water (D2O) uptake studies, while for detailed examination of their structural dynamics, networks were studied using 13C magic angle spinning NMR (13C MAS NMR) spectroscopy, 1H double quantum NMR (1H DQ NMR) spectroscopy, and 1H pulsed field gradient NMR (1H PFG NMR) spectroscopy. These solid state NMR results revealed that the networks were composed of a two component structure, having different dipolar coupling constants. The diffusion of solvent molecules depended on the degree of swelling that was imparted to the network by the varying chain length of the PEG based cross-linking agent.

Investigation on the Promoter-Induced Rapid Non-Aqueous Media Synthesis of SAPO-35 and Methanol-to-Olefin Reaction.

Microporous SAPO-35 molecular sieves (Levyne type) were synthesized in non-aqueous media by using different inorganic promoters (HClO4–, HF, H3PO4, and NaNO3) to enhance the rate of crystallization, and the as-synthesized materials were characterized by using different methods such as powder X-ray diffraction spectroscopy (PXRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), magic angle spinning-nuclear magnetic resonance spectroscopy (MAS-NMR), Brunauer–Emmett–Teller (BET) analysis, and X-ray photoelectron spectroscopy (XPS). From PXRD patterns, it was found that all the materials have a highly crystalline nature without any other impurities. SEM images reveal rhombohedral particles in all synthesis conditions. The framework structure of the synthesized materials was identified by FT-IR spectroscopy, and it reveals that all materials gave a similar framework structure. From BET and XPS, we have confirmed that the pore size and pore diameters along with the elemental compositions have a minor change. The 27Al, 31P, and 29Si MAS-NMR spectra of all the promoter-based SAPO-35 materials are close to those of the standard SAPO-35 material. All the above characterization studies reveal the formation of SAPO-35 in a short time with promoters. The catalytic application studies of these synthesized materials for a methanol-to-olefin conversion reaction were performed, and the efficiency of these materials was found to be similar to that of standard materials.

Unexpected behavior of commercial artists’ acrylic paints under UVA artificial aging

The study of the behavior of acrylic paints after UV-A (400–300 nm, near UV) artificial exposure was further investigated by extending it to more commercially available artists’ acrylic paints. The accelerated aging of eight acrylic-based commercial paints was studied using a combination of analytical techniques including Nuclear Magnetic Resonance (NMR) spectroscopies, Pyrolysis coupled with Gas Chromatography/Mass Spectrometry (Py-GC/MS), Fourier Transform Infrared in ATR mode (FTIR-ATR), Direct Analysis in Real Time coupled to Mass Spectrometry (DART-MS) and microscopic techniques, such as Stereoscopic Microscopy (SM) and Scanning Electron Microscopy coupled with Energy Dispersive X-ray Spectroscopy (SEM-EDS). All the aging process was characterized and monitored to study the signs of decay. During the aging process a gradual loss of the organic surfactant occurred in all the paints, similar to the results contained in a previous study. Interestingly, two of the studied paints presented an unexpected behavior related to the properties of the acrylic binder. In one of such paints solid-state 13C Cross Polarization Magic Angle Spinning (13C CPMAS) NMR spectroscopy was performed. The results obtained by changing the recycled delay and carrying out variable temperature experiments, suggested a change in the internal mobility of the aged sample that could be attributed to the presence of ionomers.According to this study, the aging of acrylic binders may not be the same in all paints and may be affected by the interaction of different components of the formulation. Understanding these processes will give more tools for the preservation of modern art paintings and cultural heritage since this type of commercial paints and other conservation materials of the same composition were extensively used during the 20th century.

A Theoretical Study on a Novel Cartesian Product Operator Formalism Applicable to Strongly-Coupled Two-Spin 1/2 Systems in Solution-State and Solid-State MAS NMR Spectroscopy

Abstract In solution-state and solid-state MAS (Magic Angle Spinning) NMR (Nuclear Magnetic Resonance) spectroscopy, a comprehensive product operator formalism applicable to general two-spin 1/2 systems, including strongly-coupled systems, is proposed. The formalism employs standard product operators, based on the orthogonal coordinate system, easily evaluating the effects of RF (Radio Frequency) pulse sequences. Solid-state anisotropic interactions modulated by MAS are treated in the perturbation theory, yielding striking solid-state effects, whereas the absence of those interactions leads to solution-state cases with strong couplings. Solid-state MAS INADEQUATE spectra are found to give rise to auto-correlation signals even for the spin pairs possessing an identical isotropic chemical shift.