Search

We use 1H, 2H, and 7Li nuclear magnetic resonance to investigate local and diffusive dynamics of LiCl-7H2O and LiCl-7D2O solutions in pristine and functionalized silica nanopores in a component-selective manner. Recently, we showed that the solution dynamics become slower when the diameter of the pristine pores is reduced. Here, we determine the effects of (aminopropyl)triethoxysilane and dye surface functionalizations on the motions of the water molecules and lithium ions from ambient temperatures down to the glass transition. The local and diffusive solution dynamics are similar in both functionalized pores but, on average, slower than in pristine pores with comparable diameters. When the exchange between different confinement regions is sufficiently slow at reduced temperatures, bimodal water and lithium dynamics may be observed. We attribute this bimodality to bulk-like motion in the pore centers and slowed-down motion at the pore walls. For the lithium ions, a bimodality observed in the pristine pores is absent in the functionalized ones. We conjecture that the steric hindrance and electrostatic interactions associated with the grafted functional groups interfere with the formation of a defined electric double layer, while the enhanced surface roughness and unequal charge distribution result in overall slower dynamics. Thus, the nature of the walls is an important parameter for the solution dynamics. Thereby, in situ measurements of the pH value inside the silica pores using the grafted dye molecules reveal that observed changes in the pH value in response to the surface functionalization are of limited relevance for the water reorientation. [ABSTRACT FROM AUTHOR]

We use 1H, 2H, and 7Li NMR to investigate the molecular dynamics of glass-forming LiCl-7H2O and LiCl-7D2O solutions confined to MCM-41 or SBA-15 silica pores with diameters in the range of d = 2.8 nm–5.4 nm. Specifically, it is exploited that NMR experiments in homogeneous and gradient magnetic fields provide access to local and diffusive motions, respectively, and that the isotope selectivity of the method allows us to characterize the dynamics of the water molecules and the lithium ions separately. We find that the silica confinements cause a slowdown of the dynamics on all length scales, which is stronger at lower temperatures and in narrower pores and is more prominent for the lithium ions than the water molecules. However, we do not observe a temperature-dependent decoupling of short-range and long-range dynamics inside the pores. 7Li NMR correlation functions show bimodal decays when the pores are sufficiently wide (d > 3 nm) so that bulk-like ion dynamics in the pore centers can be distinguished from significantly retarded ion dynamics at the pore walls, possibly in a Stern layer. However, we do not find evidence for truly immobile fractions of water molecules or lithium ions and, hence, for the existence of a static Stern layer in any of the studied silica pores. [ABSTRACT FROM AUTHOR]

The effect of mechanical deformation on the formation of quasicrystals in Zr57Ti8Nb2.5Cu13.9Ni11.1Al7.5 glassy ribbons has been investigated. The mechanical treatment drastically affects the crystallization behavior and, in particular, suppresses primary quasicrystal formation. However, quasicrystals can be formed by the addition of the appropriate amount of zirconium. This indicates that if a particular short-range order (e.g., icosahedral) is required for quasicrystal formation and if this short-range order is altered during milling, it can be restored by appropriately adjusting the chemical composition. [ABSTRACT FROM AUTHOR]

We report pure zero field nuclear magnetic resonance (NQR) measurements on the optimally doped three layer high-Tc-compounds HgBaCaCuO and HgBaCaCuO(F) with Tc=134 K. Above Tc two Cu NQR line pairs are observed in the spectra corresponding to the two inequivalent Cu lattice sites. Below Tc the Cu NQR spectra show additional lines leading to the extreme broadened Cu NQR spectra at 4.2 K well known for the HgBaCaCuO compounds. The spin–lattice relaxation curves follow a triple exponential function with coefficients depend onto the saturation time (number of saturation pulses), whereas the spin–spin relaxation curve is described by a single exponential function. From the spin–lattice relaxation we deduced a complete removal of the Kramers degeneracy of the Cu quadrupole levels indicating that the additional lines are due to a Zeemann splitting of the 63/65Cu lines due to the spontaneous formation of magnetic moments within the CuO layers. Below 140 K, the spectra are well fitted by a number of 6 63/65Cu line pairs. From the number of the Cu lines, the position of the lines relative to each other and the complete removal of the Kramers degeneracy we deduced an orientation of the magnetic moments parallel to the c-axis with magnitudes of the order of 1000 G. We also discuss the possible microscopic origin of the observed internal magnetic fields. [Copyright &y& Elsevier]

Hg-oxide ceramic high temperature superconductors were studied byHg andCu NMR spectroscopy. Room temperature spectra, spin-spin and spin-lattice relaxation times of samples with different superconducting transition temperatures are presented. A spin-lattice relaxation time of T =35 msec and a spin-spin relaxation time of T =1.6 msec were found for theHg NMR. All samples exhibit similar characteristic powder spectra caused by an axially symmetricHg spin interaction. The isotropic value and the anisotropy of the tensor relative to solid HgCl as a standard substance is estimated. Furthermore, results ofCu NMR measurements at a temperature of 4.2 K which exhibit a typical powder line shape (for I=3/2) are presented. [ABSTRACT FROM AUTHOR]

We report pure zero field nuclear magnetic resonance (NQR) measurements on the optimally doped three layer compound Hg1Ba2Ca2Cu3O8+δ (Hg-1223) with Tc=134 K. Above Tc two Cu line pairs are observed in the spectrum corresponding to the two inequivalent Cu lattice sites. Below Tc the Cu NQR spectrum shows a splitting of these two line pairs into six line pairs. From a multiexponential spin lattice relaxation with a dependency on the initial conditions, we find a formation of magnetic moments in the CuO layers as the origin of the line splitting. Furthermore, the magnetic moments are oriented parallel to the symmetry axis of the electrical field gradient tensor with magnitudes of the order of 1000 G. [Copyright &y& Elsevier]

In this work, we report on an improved cell assembly of cylindrical electrochemical cells for 23 Na in-situ solid-state NMR (ssNMR) investigations. The cell set-up is suitable for using powder electrode materials. Reproducibility of our cell assembly is analyzed by preparing two cells containing hard carbon (HC) powder as working electrode and sodium metal as reference electrode. Electrochemical storage properties of HC powder electrode derived from carbonization of sustainable cellulose are studied by ssNMR. 23 Na in-situ ssNMR monitors the sodiation/desodiation of a Na|NaPF 6 |HC cell (cell 1) over a period of 22 days, showing high cell stability. After the galvanostatic process, the HC powder material is investigated by high resolution 23 Na ex-situ MAS NMR. The formation of ionic sodium species in different chemical environments is obtained. Subsequently, a second Na|NaPF 6 |HC cell (cell 2) is sodiated for 11 days achieving a capacity of 220 mAh/g. 23 Na ex-situ MAS NMR measurements of the HC powder material extracted from this cell clearly indicate the presence of quasi-metallic sodium species next to ionic sodium species. This observation of quasi-metallic sodium species is discussed in terms of the achieved capacity of the cell as well as of side reactions of sodium in this electrode material., (© 2023 The Authors. ChemSusChem published by Wiley-VCH GmbH.)

Polymer-derived silicon oxycarbide ceramics (SiCO) have been considered as potential anode materials for lithium- and sodium-ion batteries. To understand their electrochemical storage behavior, detailed insights into structural sites present in SiCO are required. In this work, the study of local structures in SiCO ceramics containing different amounts of carbon is presented. 13 C and 29 Si solid-state MAS NMR spectroscopy combined with DFT calculations, atomistic modeling, and EPR investigations, suggest significant changes in the local structures of SiCO ceramics even by small changes in the material composition. The provided findings on SiCO structures will contribute to the research field of polymer-derived ceramics, especially to understand electrochemical storage processes of alkali metal/ions such as Na/Na + inside such networks in the future., (© 2023 The Authors. ChemSusChem published by Wiley-VCH GmbH.)

Lead zirconate (PbZrO 3 , PZ) is a prototype antiferroelectric (AFE) oxide from which state-of-the-art energy storage materials are derived by chemical substitutions. A thorough understanding of the structure-property relationships of PZ-based materials is essential for both performance improvement and the design of more environmentally friendly replacements. (Pb 1- x Ba x )ZrO 3 (PBZ) can serve as a model system for studying the effect of A-site substitution in the perovskite lattice, with barium destabilizing the AFE state. Here, the two-dimensional 207 Pb solid-state NMR spectra of PZ and PBZ were recorded to analyze the local structural role of barium substitution. At low substitution levels, 207 Pb NMR spectroscopy reveals the presence of Pb-O bond length disorder. Upon crossing the threshold value of x for the macroscopic phase transition into a ferroelectric (FE) state, the barium cations cause local-scale lattice expansions in their vicinity, resulting in the collapse of two lead lattice sites into one. The stabilization of the larger volume site coincides with the favoring of larger lead displacements. We also observed more covalent bonding environments which may originate from the lower polarizability of the barium cations, facilitating the formation of stronger Pb-O bonds in their vicinity. From the local structural point of view, we propose that the substitution-induced AFE → FE phase transition is therefore related to an increasing correlation of larger lead displacements in larger oxygen cavities as the barium content increases. Our results also highlight 207 Pb NMR spectroscopy as a valuable method for the characterization of the structure-property relationships of PbZrO 3 -based AFE and FE oxides.

High-field dynamic nuclear polarization is a powerful tool for the structural characterization of species on the surface of porous materials or nanoparticles. For these studies the main source of polarization are radical-containing solutions which are added by post-synthesis impregnation of the sample. Although this strategy is very efficient for a wide variety of materials, the presence of the solvent may influence the chemistry of functional species of interest. Here we address the development of a comprehensive strategy for solvent-free DNP enhanced NMR characterization of functional (target) species on the surface of mesoporous silica (SBA-15). The strategy includes the partial functionalization of the silica surface with Carboxy-Proxyl nitroxide radicals and target Fmoc-Glycine functional groups. As a proof of principle, we have observed for the first time DNP signal enhancements, using the solvent-free approach, for 13C{1H} CPMAS signals corresponding to organic functionalities on the silica surface. DNP enhancements of up to 3.4 were observed for 13C{1H} CPMAS, corresponding to an experimental time save of about 12 times. This observation opens the possibility for the DNP-NMR study of surface functional groups without the need of a solvent, allowing, for example, the characterization of catalytic reactions occurring on the surface of mesoporous systems of interest. For 29Si with direct polarization NMR, up to 8-fold DNP enhancements were obtained. This 29Si signal enhancement is considerably higher than the obtained with similar approaches reported in literature. Finally, from DNP enhancement profiles we conclude that cross-effect is probably the dominant polarization transfer mechanism.

We prepare various amino-acid functionalized silica pores with diameters of ∼6 nm and study the temperature-dependent reorientation dynamics of water in these confinements. Specifically, we link basic Lys, neutral Ala, and acidic Glu to the inner surfaces and combine 2 H nuclear magnetic resonance spin-lattice relaxation and line shape analyses to disentangle the rotational motions of the surfaces groups and the crystalline and liquid water fractions coexisting below partial freezing. Unlike the crystalline phase, the liquid phase shows reorientation dynamics, which strongly depends on the chemistry of the inner surfaces. The water reorientation is slowest for the Lys functionalization, followed by Ala and Glu and, finally, the native silica pores. In total, the rotational correlation times of water at the different surfaces vary by about two orders of magnitude, where this span is largely independent of the temperature in the range ∼200-250 K.

We report here on structure-related aggregation effects of short-range ordered aluminosilicates (SROAS) that have to be considered in the development of synthesis protocols and may be relevant for the properties of SROAS in the environment. We synthesized SROAS of variable composition by neutralizing aqueous aluminium chloride with sodium orthosilicate at ambient temperature and pressure. We determined elemental composition, visualized morphology by microscopic techniques, and resolved mineral structure by solid-state 29 Si and 27 Al nuclear magnetic resonance and Fourier-transform infrared spectroscopy. Nitrogen sorption revealed substantial surface loss of Al-rich SROAS that resembled proto-imogolite formed in soils and sediments due to aggregation upon freezing. The effect was less pronounced in Si-rich SROAS, indicating a structure-dependent effect on spatial arrangement of mass at the submicron scale. Cryomilling efficiently fractured aggregates but did not change the magnitude of specific surface area. Since accessibility of surface functional groups is a prerequisite for sequestration of substances, elucidating physical and chemical processes of aggregation as a function of composition and crystallinity may improve our understanding of the reactivity of SROAS in the environment.

A facile approach is reported for the preparation of dirhodium coordination polymers [Rh 2 (L1) 2 ] n (Rh 2 -L1) and [Rh 2 (L2) 2 ] n (Rh 2 -L2; L1=N,N'-(pyromellitoyl)-bis-L-phenylalanine diacid anion, L2=bis-N,N'-(L-phenylalanyl) naphthalene-1,4,5,8-tetracarboxylate diimide) from chiral dicarboxylic acids by ligand exchange. Multiple techniques including FTIR, XPS, and 1 H→ 13 C CP MAS NMR spectroscopy reveal the formation of the coordination polymers. 19 F MAS NMR was utilized to investigate the remaining TFA groups in the obtained coordination polymers, and demonstrated near-quantitative ligand exchange. DR-UV-vis and XPS confirm the oxidation state of the Rh center and that the Rh-single bond in the dirhodium node is maintained in the synthesis of Rh 2 -L1 and Rh 2 -L2. Both coordination polymers exhibit excellent catalytic performance in the asymmetric cyclopropanation reaction between styrene and diazooxindole. The catalysts can be easily recycled and reused without significant reduction in their catalytic efficiency., (© 2020 The Authors. Published by Wiley-VCH GmbH.)

We present a facile approach to encapsulate functional porous organic cages (POCs) into a robust MOF by an incipient-wetness impregnation method. Porous cucurbit[6]uril (CB6) cages with high CO 2 affinity were successfully encapsulated into the nanospace of Cr-based MIL-101 while retaining the crystal framework, morphology, and high stability of MIL-101. The encapsulated CB6 amount is controllable. Importantly, as the CB6 molecule with intrinsic micropores is smaller than the inner mesopores of MIL-101, more affinity sites for CO 2 are created in the resulting CB6@MIL-101 composites, leading to enhanced CO 2 uptake capacity and CO 2 /N 2 , CO 2 /CH 4 separation performance at low pressures. This POC@MOF encapsulation strategy provides a facile route to introduce functional POCs into stable MOFs for various potential applications., (© 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

New acetylenedicarboxylate (ADC) and chlorofumarate (Fum-Cl) based hafnium-metal-organic frameworks have been synthesized by alternatively reacting acetylenedicarboxylic acid in DMF or water with appropriate hafnium salt, in the presence of acetic acid modulator. The two materials of respective ideal formulas [Hf 6 O 4 (OH) 4 (ADC) 6 ] (Hf-HHU-1) and [Hf 6 O 4 (OH) 4 (Fum-Cl) 6 ] (Hf-HHU-2) have been structurally characterized by powder X-ray diffraction to be UiO-66 isostructural, consisting of octahedral [Hf 6 O 4 (OH) 4 ] 12+ secondary building units each connected to other units by 12 ADC or Fum-Cl linkers into a microporous network with fcu topology. This structure was confirmed by Rietveld refinement. Hf-HHU-2 is formed by in situ hydrochlorination of acetylenedicarboxylic acid to chlorofumarate. Its presence has been determined by combined Raman spectroscopy, solid-state NMR, scanning electron microscopy, energy dispersive X-ray and X-ray photoelectron spectroscopies. Hf-HHU-1 and Hf-HHU-2 exhibit very high hydrophilicity as revealed by their water sorption profiles, meanwhile Hf-HHU-2 adsorbs CO 2 with an isosteric heat of 39 kJ mol -1 . Hf-HHU-2 also adsorbs molecular iodine vapor exclusively as polyiodide anions due to grafted chloro-functions on the pores surface. It has been observed that defective nanodomains with reo tolopology can be introduced in the structure of Hf-HHU-2 by variation of the linker to metal-salt molar ratio.

The structure and surface functionalization of biologically relevant silica-based hybrid materials was investigated by 2D solid-state NMR techniques combined with dynamic nuclear polarization (DNP). This approach was applied to a model system of mesoporous silica, which was modified through in-pore grafting of small peptides by solid-phase peptide synthesis (SPPS). To prove the covalent binding of the peptides on the surface, DNP-enhanced solid-state NMR was used for the detection of 15 N NMR signals in natural abundance. DNP-enhanced heterocorrelation experiments with frequency switched Lee-Goldburg homonuclear proton decoupling ( 1 H- 13 C and 1 H- 15 N CP MAS FSLG HETCOR) were performed to verify the primary structure and configuration of the synthesized peptides. 1 H FSLG spectra and 1 H- 29 Si FSLG HETCOR correlation spectra were recorded to investigate the orientation of the amino acid residues with respect to the silica surface. The combination of these NMR techniques provides detailed insights into the structure of amino acid functionalized hybrid compounds and allows for the understanding for each synthesis step during the in-pore SPPS., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Diatom biosilica are highly complex inorganic/organic hybrid materials. To get deeper insights on their structure at a molecular level, model systems that mimic the complex natural compounds were synthesized and characterized. A simple and efficient peptide immobilization strategy was developed, which uses a well-ordered porous silica material as a support and commercially available Fmoc-amino acids, similar to the known solid-phase peptide synthesis. As an example, Fmoc-glycine and Fmoc-phenylalanine are immobilized on the silica support. The success of functionalization was investigated by 13 C CP MAS and 29 Si CP MAS solid-state NMR. Thermogravimetric analysis (TGA) and elemental analysis (EA) were performed to quantify the functionalization. Changes of the specific surface area, pore volume, and pore diameters in all modification steps were studied by Brunauer-Emmett-Teller based nitrogen adsorption-desorption measurements (BET). The combination of the analytical methods provided high grafting densities of 2.1±0.2 molecules/nm 2 on the surface. Furthermore, they allowed for monitoring chemical changes on the pore surface and changes of the pore properties of the material during the different functionalization steps. This universal approach is suitable for the selective synthesis of pores with tunable surface-peptide functionalization, with applications to the synthesis of a big variety of silica-peptide model systems, which in the future may lead to a deeper understanding of complex biological systems., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A strategy was developed to obtain from acetylenedicarboxylic acid either an acetylenedicarboxylate-based Zr IV metal-organic framework (MOF) with fcu topology or a halo-functionalized-MOF-801 through in situ ligand hydrohalogenation. The new materials feature exceptionally high hydrophilicity and CO 2 /H 2 adsorption energetics. The acetylenedicarboxylate linker and its functionalizable triple-bond discloses its potential in the engineering of microporous materials with targeted properties., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The Ruddlesden-Popper (K 2 NiF 4 ) type phase La 2 NiO 3 F 2 was prepared via a polymer-based fluorination of La 2 NiO 4+ d . The compound was found to crystallize in the orthorhombic space group Cccm ( a = 12.8350(4) Å, b = 5.7935(2) Å, c = 5.4864(2) Å). This structural distortion results from an ordered half occupation of the interstitial anion layers and has not been observed previously for K 2 NiF 4 -type oxyfluoride compounds. From a combination of neutron and X-ray powder diffraction and 19 F magic-angle spinning NMR spectroscopy, it was found that the fluoride ions are only located on the apical anion sites, whereas the oxide ions are located on the interstitial sites. This ordering results in a weakening of the magnetic Ni-F-F-Ni superexchange interactions between the perovskite layers and a reduction of the antiferromagnetic ordering temperature to 49 K. Below 30 K, a small ferromagnetic component was found, which may be the result of a magnetic canting within the antiferromagnetic arrangement and will be the subject of a future low-temperature neutron diffraction study. Additionally, density functional theory-based calculations were performed to further investigate different anion ordering scenarios.

The design and application of a versatile and inexpensive experimental extension to NMR spectrometers is described that allows to carry out highly reproducible PHIP experiments directly in the NMR sample tube, i.e. under PASADENA condition, followed by the detection of the NMR spectra of hyperpolarized products with high spectral resolution. Employing this high resolution it is feasible to study kinetic processes in the solution with high accuracy. As a practical example the dissolution of hydrogen gas in the liquid and the PHIP kinetics during the hydrogenation reaction of Fmoc-O-propargyl-l-tyrosine in acetone-d 6 are monitored. The timing of the setup is fully controlled by the pulse-programmer of the NMR spectrometer. By flushing with an inert gas it is possible to efficiently quench the hydrogenation reaction in a controlled fashion and to detect the relaxation of hyperpolarization without a background reaction. The proposed design makes it possible to carry out PHIP experiments in an automatic mode and reliably determine the enhancement of polarized signals., (Copyright © 2017 Elsevier Inc. All rights reserved.)

The spinning sidebands envelope of satellite transitions often display an asymmetric shape, which is caused by an asymmetric response of the NMR probe circuit. In this work, we revisit the basic concepts of the RLC circuit at the heart of every NMR probe and present two approaches capable of minimizing this artifact. While the first one consists of deliberately mistuning the probe, the second one relies on measuring the probe's response function and deconvoluting its contribution from the spectra. Both approaches are validated with 23 Na NMR spectra of a lead-free relaxor ferroelectric (BNT-1BT). This material is particularly suitable as an example of the applicability of both strategies for samples with a disordered local structure., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Lead-based relaxor ferroelectrics are key functional materials indispensable for the production of multilayer ceramic capacitors and piezoelectric transducers. Currently there are strong efforts to develop novel environmentally benign lead-free relaxor materials. The structural origins of the relaxor state and the role of composition modifications in these lead-free materials are still not well understood. In the present contribution, the solid-solution (100-x)(Bi1/2Na1/2)TiO3-xBaTiO3 (BNT-xBT), a prototypic lead-free relaxor is studied by the combination of solid-state nuclear magnetic resonance (NMR) spectroscopy, dielectric measurements and ab-initio density functional theory (DFT). For the first time it is shown that the peculiar composition dependence of the EFG distribution width (ΔQISwidth) correlates strongly to the dispersion in dielectric permittivity, a fingerprint of the relaxor state. Significant disorder is found in the local structure of BNT-xBT, as indicated by the analysis of the electric field gradient (EFG) in (23)Na 3QMAS NMR spectra. Aided by DFT calculations, this disorder is attributed to a continuous unimodal distribution of octahedral tilting. These results contrast strongly to the previously proposed coexistence of two octahedral tilt systems in BNT-xBT. Based on these results, we propose that considerable octahedral tilt disorder may be a general feature of these oxides and essential for their relaxor properties.

The successful synthesis and solid state NMR characterization of silica-based organic-inorganic hybrid materials is presented. For this, collagen-like peptides are immobilized on carboxylate functionalized mesoporous silica (COOH/SiOx) materials. A pre-activation of the silica material with TSTU (O-(N-Succinimidyl)-N,N,N',N'-tetramethyluronium tetrafluoroborate) is performed to enable a covalent binding of the peptides to the linker. The success of the covalent immobilization is indicated by the decrease of the (13)C CP-MAS NMR signal of the TSTU moiety. A qualitative distinction between covalently bound and adsorbed peptide is feasible by (15)N CP-MAS Dynamic Nuclear Polarization (DNP). The low-field shift of the (15)N signal of the peptide's N-terminus clearly identifies it as the binding site. The DNP enhancement allows the probing of natural abundance (15)N nuclei, rendering expensive labeling of peptides unnecessary., (Copyright © 2015 Elsevier Inc. All rights reserved.)