23Na Magic Angle Spinning Nuclear Magnetic Resonance Research Articles

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.

Spherical silica particles coated with lamellar nanocomposites based on a hydrophobic functionalized phyllosilicate

The surface of spherical silica particles (monodisperse, 2.6 µm) was modified with inorganic–organic lamellar ordered hybrids for applications as hydrophobic dye supports in cosmetics. The inorganic–organic multilayers comprised a 2:1 phyllosilicate (two sheets of linked SiO4 tetrahedra with one sheet of M2–3(OH)6 octahedra, where M is either magnesium or aluminum), consisting of octyl chains directly bonded to the inorganic sheets via Si–C covalent bonds. Octyltriethoxysilane was allowed to react at room temperature with spherical silica and aluminum acetylacetonate in a mixed aqueous solution of NaOH and NaCl at pH 10. The formation of a 2:1 phyllosilicate grafted with an octyl chain was confirmed by X-Ray powder diffraction, where a lamellar structure with the d001 value of 2.4 nm was displayed. The lamellar structure included the isomorphic substitution of Si by Al and the formation of C–Si–O–Aloct bonds, as shown in 29Si–and 27Al–magic angle spinning (MAS)–nuclear magnetic resonance (NMR) spectra. Further, the 23Na–MAS NMR spectrum indicated the incorporation of Na aquo complex cations into the organophyllosilicate. The hydrated Na ions were exchanged with a cationic dye (methylene blue) to be adsorbed. An anionic dye (Phloxine B), which has frequently been used as cosmetic pigments, was adsorbed onto the resulting hybrid particles when Al3+ was present in the dye solution. The hydrophobic dye supports can be used instead of plastic beads to reduce marine pollution.

MAS-NMR studies of carbonate retention in a very wide range of Na2O-SiO2 glasses

Glasses that contain carbon are of geological interest, and the form of that carbon can be probed by Magic-Angle Spinning Nuclear Magnetic Resonance (MAS-NMR) spectroscopy. Previous studies of the Na2O-SiO2 glass system could only reach 56 mol% Na2O. Here we reproduce and extend those studies to cover a very wide compositional range, from 20 to 70 mol% Na2O, by using a combination of conventional melt-quench and twin roller quenching technologies on natural and 99% 13C-enriched sodium silicate glasses. 13C MAS-NMR reveals that measurable levels of carbon retention occur above at least 40 mol% Na2O, and takes the form of CO32− ions incorporated in the glass structure. These CO32− anions are surrounded by Na+ cations, forming nanoscale domains in a sodium silicate glass network. 23Na MAS-NMR showed a linear decrease in mean Na—O bond length with increasing Na2O content, up to 60 mol% Na2O, above which the mean Na—O bond length increased. Elemental analysis detected significant (>5%) carbon dioxide by mass in the 65 and 70 mol% Na2O glasses. For the 70 mol% Na2O glass, 13C and 23Na MAS-NMR detected ordered nanoscale domains composed of only Na2O and CO2. These results have shown the quantity and nature of carbon retention in the archetypal sodium silicate glass system, which will better inform structural models and carbonate solubility limits.

Elementary Steps of Faujasite Formation Followed by in Situ Spectroscopy

Ex situ and in situ spectroscopy was used to identify the kinetics of processes during the formation of the faujasite (FAU) zeolite lattice from a hydrous gel. Using solid-state 27Al magic angle spinning (MAS) nuclear magnetic resonance (NMR), the autocatalytic transformation from the amorphous gel into the crystalline material was monitored. Al X-ray absorption near-edge structure shows that most Al already adopts a tetrahedral coordination in the X-ray-amorphous aluminosilicate at the beginning of the induction period, which hardly changes throughout the rest of the synthesis. Using 23Na NMR spectroscopy, environments in the growing zeolite crystal were identified and used to define the processes in the stepwise formation of the zeolite lattice. The end of the induction period was accompanied by a narrowing of the 27Al and 23Na MAS NMR peak widths, indicating the increased level of long-range order. The experiments show conclusively that the formation of faujasite occurs via the continuous formation and...

Physical properties and MAS-NMR studies of titanium phosphate-based glasses

In this study, for a series phosphate-based glasses ((P2O5)0.45(CaO)0.3(Na2O)0.25−x(TiO2)x, 0 ≤ x ≤ 0.15), their degradation, ion release, surface and thermal properties have been determined. The results show that adding TiO2 was associated with a significant increase in density and glass transition temperature, but a decrease in degradation rate and ion release. 31P solid-state magic-angle-spinning nuclear magnetic resonance (MAS-NMR) showed that the local structure of the glasses changes with increasing TiO2 content. As TiO2 is incorporated into the glass, the phosphate connectivity increases as Q1 units transform to Q2, confirming that an increase in the nominal TiO2 content correlates unequivocally with an increase in glass stability. As reported for titania–silica gels, Ti4+ is clearly adopting a network former role in these phosphate-based glasses. 23Na MAS-NMR results corroborate this phenomenon with a marked upfield trend of the 23Na isotropic chemical shift suggesting that the local Na–O bond distances are decreasing within a more condensed glass network upon increased incorporation of TiO2.

29Si, 27Al, 1H and 23Na MAS NMR Study of the Bonding Character in Aluminosilicate Inorganic Polymers

Si-29, Al-27, H-1 and Na-23 solid-state magic-angle spinning (MAS) nuclear magnetic resonance (NMR) has been used to relate nominal composition, bonding character and compressive strength properties in aluminosilicate inorganic polymers (AIPs). The Si-29 chemical shift varies systematically with Si-to-Al ratio, indicating that the immediate structural environment of Si is altering with nominal composition. Fast H-1 MAS and Si-29 T (SiH)/T-1 rho relaxation measurements demonstrated that occluded pore H2O mobility within the disordered cavities is slow in comparison with H2O mobility characteristics observed within the ordered channel structures of zeolites. The Al-27 MAS NMR data show that the Al coordination remains predominantly 4-coordinate. In comparison with the Si-29 MAS data, the corresponding Al-27 MAS line shapes are relatively narrow, suggesting that the AlO4 tetrahedral geometry is largely unperturbed and the dominant source of structural disorder is propagated by large distributions of Si-O bond angles and bond lengths. Corresponding Na-23 MAS and multiple-quantum MAS NMR data indicate that Na speciation is dominated by distributions of hydration states; however, more highly resolved Na-23 resonances observed in some preparations supported the existence of short-range order. New structural elements are proposed to account for the existence of these Na resonances and an improved model for the structure of AIPs has also been proposed.

NMR Studies of Heat-Induced Transitions in Structure and Cation Binding Environments of a Strontium-Saturated Swelling Mica

In this work, we combine 27Al, 29Si, 19F, and 23Na magic-angle spinning (MAS) nuclear magnetic resonance (NMR) to characterize the structure and interlayer cation environments in a strontium-saturated member of the swelling mica family before and after a heat-induced collapse of the interlayer space. The 27Al and 29Si MAS NMR demonstrate that the sample consists mainly of swelling mica, though the composition does not match the ideal structural formula. Aluminum NMR also shows that a portion of the aluminum shifts from a tetrahedral to an octahedral coordination environment upon heating. Changes in the 29Si and 19F NMR after heating are consistent with a structural rearrangement of the tetrahedral sheet to permit the binding of larger cations in the ditrigonal cavity. The 23Na MAS NMR results indicate the presence of three unique sodium environments before and after heating. The heat-invariant resonance is consistent with the presence of sodium carbonate. The other two resonances are associated with interlayer sodium and reflect a migration of sodium to a dominantly anhydrous ditrigonal binding structure with heating. Quantitative elemental analysis and NMR data presented here suggest strontium is bound deep within the ditrigonal cavity of the collapsed micas.

Phosphate speciation in sodium borosilicate glasses studied by nuclear magnetic resonance

The structure of RNa2O·B2O3·KSiO2·xP2O5 (0.5<R<2; 0.86<K<3) borosilicate glasses has been studied by nuclear magnetic resonance (NMR). 31P magic angle spinning (MAS), double quantum-magic angle spinning (DQ-MAS) and 31P–11B transfer of populations under double resonance magic angle spinning (TRAPDOR MAS) NMR were used to determine the phosphate speciation in the glasses and their connectivity with the borosilicate network. The structure of the glass network was characterized with 11B, 29Si and 23Na MAS NMR. Ab initio calculations of the 31P chemical shielding were carried out in order to confirm the connectivity between phosphorus and the structural units of the borosilicate glass network. Na3PO4 (monophosphate), Na4P2O7 (diphosphate) and P–O–B species (mono- and diphosphate groups with borate units as the next nearest neighbors) are found all along the compositional range studied. The proportion of the P–O–B groups increases as the glass optical basicity decreases, while the proportions of mono- and diphosphate species decrease. The change in the glass transition temperature of the phospho-borosilicate glasses with respect to that of the borosilicate ones is discussed in terms of the structural characterization. The formation of phosphate species gives rise to the increase in Tg, which is attributed to the re-polymerization of the silicate network, while the formation of P–O–B bonds weakens the glass network and produces a decrease in the glass transition temperature.

The distribution of sodium ions in aluminosilicate glasses: a high-field Na-23 MAS and 3Q MAS NMR study

The local configurations around sodium ions in silicate glasses and melts and their distributions have strong implications for the dynamic and static properties of melts and thus may play important roles in magmatic processes. The quantification of distributions among charge-balancing cations, including Na + in aluminosilicate glasses and melts, however, remains a difficult problem that is relevant to high-temperature geochemistry as well as glass science. Here, we explore the local environment around Na + in charge-balanced aluminosilicate glasses (the NaAlO 2-SiO 2 join) and its distribution using 23Na magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy at varying magnetic fields of 9.4, 14.1, and 18.8 T, as well as triple-quantum (3Q)MAS NMR spectroscopy at 9.4 T, to achieve better understanding of the extent of disorder around this cation. We quantify the extent of this disorder in terms of changes in Na-O distance ( d[Na-O]) distributions with composition and present a structural model favoring a somewhat ordered Na distribution, called a “perturbed” Na distribution model. The peak position in 23Na MAS spectra of aluminosilicate glasses moves toward lower frequencies with increasing Si/Al ratios, implying that the average d(Na-O) increases with increasing R. The peak width is significantly reduced at higher fields (14.1 and 18.8 T) because of the reduced effect of second-order quadrupolar interaction, and 23Na MAS NMR spectra thus provide relatively directly the Na chemical shift distribution and changes in atomic environment with composition. Chemical shift distributions obtained from 23Na 3Q MAS spectra are consistent with MAS NMR data, in which deshielding decreases with R. The average distances between Na and the three types of bridging oxygens (BOs) (Na-{Al-O-Al}, Na-{Si-O-Al}, and Na-{Si-O-Si}) were obtained from the correlation between d(Na-O) and isotropic chemical shift. The calculated d(Na-{Al-O-Al}) of 2.52 Å is shorter than the d(Na-{Si-O-Si}) of 2.81 Å, and d(Na-{Al-O-Al}) shows a much narrower distribution than the other types of BOs. 23Na chemical shifts in binary (Al-free) sodium silicate glasses are more deshielded and have ranges distinct from those of aluminosilicate glasses, implying that d(Na-NBO) (nonbridging oxygen) is shorter than d(Na-BO) and that d(Na-{Si-O-Si}) in binary silicates can be shorter than that in aluminosilicate glasses. The results given here demonstrate that high-field 23Na NMR is an effective probe of the Na + environment, providing not only average structural information but also chemically and topologically distinct chemical shift ranges (distributions) and their variation with composition and their effects on static and dynamic properties.

Different water solubility mechanisms in hydrous glasses along the Qz-Ab join:: Evidence from NMR spectroscopy

The compositional dependence of water incorporation mechanisms in melts and glasses belonging to the quartz (Qz)-albite (Ab) join was studied with nuclear magnetic resonance (NMR) spectroscopy. Dry and hydrous glasses (containing 3.8 ± 0.1 wt% water) ranging in composition from Qz 90Ab 10 to Qz 28Ab 72 (in wt%) were synthesised and studied with 1H, 23Na, 27Al and 29Si magic angle spinning (MAS) NMR and 1H- 29Si cross polarisation (CP) MAS NMR at magnetic fields of 8.45 and 14.1 T. The results show that both molecular H 2O and OH groups are present in the hydrous glasses, represented by a broad and a narrow component in the static 1H NMR spectra. The changes in the 23Na MAS NMR spectra of the hydrated glasses indicate that sodium associates with water in all compositions studied. In contrast to the Ab-rich glasses, the 29Si MAS spectra of Qz-rich glasses (Qz 73Ab 27 - Qz 90Ab 10) change upon water incorporation, indicating the presence of Si-OH groups at least in the Qz-richest sample. The 27Al MAS data demonstrate that Al is only present in tetrahedral coordination for all glasses studied and that unless δ iso for Al Q 4(4Si) and Al Q 3(3Si)-OH are identical, Al-OH groups cannot be present in significant concentrations. Thus, in hydrous Ab-rich glasses there is probably no significant depolymerisation as suggested by Kohn et al. (1989a). However, more 27Al data for appropriate model compounds or reliable calculations of 27Al shifts and quadrupolar coupling constants are required before this conclusion can be considered to be definitive. For Qz-rich glass compositions a second solubility mechanism involving the formation of Si-OH and depolymerisation of the silicate network is inferred. The data suggest that only in Qz-rich glasses do both mechanisms coexist.

Characterization of cancrinite synthesized in 1,3-butanediol by Rietveld analysis of powder neutron diffraction data and solid-state 23Na NMR spectroscopy

The framework structure and extraframework atoms of calcined and dehydrated cancrinite synthesized in 1,3-butanediol are characterized by powder neutron diffraction and 23Na nuclear magnetic resonance (NMR) spectroscopy. The cancrinite structure is refined in the hexagonal space group P6 3 (No. 173) with lattice parameters a=12.659 Å and c=5.153 Å. Carbonate anions are found occluded in the pores of the cancrinite structure. Although there are two different crystallographic cation sites found by the Rietveld refinement, there are three peaks in the 23Na magic-angle spinning (MAS) NMR spectrum. These peaks correspond to sodium cations found in site I inside the cancrinite cages, cations in site II inside the cancrinite pore without neighboring carbonates, and cations in site II with neighboring carbonates. Quadrupole coupling constants (QCC) obtained by a simple point-charge model agree well with the simulation of the 23Na MAS NMR spectra.

Lead exchange into zeolite and clay minerals: A 29Si, 27Al, 23Na solid-state NMR study

Chabazite, vermiculite, montmorillonite, hectorite, and kaolinite were used to remove Pb, through ion exchange, from 0.01 M aqueous Pb(NO 3) 2 solutions. These minerals contained 27 (Nachabazite), 16, 9, 9, and 0.4 wt% of Pb, respectively, after equilibration with the solutions. Ion exchange reached equilibrium within 24 h for Na-chabazite and vermiculite, but in less than 5 min for montmorillonite and hectorite. Na-chabazite took up more Pb than natural (Ca, Na)-chabazite (7 wt% Pb), whereas no such difference was observed in different cation forms of the clay minerals. Calcite impurities, associated with the clay minerals, effectively removed Pb from the aqueous solutions by the precipitation of cerussite (PbCO 3). 29Si, 27Al, and 23Na magic angle spinning (MAS) nuclear magnetic resonance (NMR), 23Na double rotation (DOR) NMR, and 23Na variable-temperature MAS NMR were used to study the ion exchange mechanisms. In Na-chabazite, cations in all three possible sites take part in the fast chemical exchange. The chemical exchange passes from the fast exchange regime to the slow regime at −80 to −100°C. One site contains a relatively low population of exchangeable cations. The other two more shielded sites contain most of the exchangeable cation. The exchangeable cations in chabazite and vermiculite were found to be close to the SiO 4 and AlO 4 tetrahedra, while those in the other clay minerals were more distant. Two sites (or groups of sites) for exchangeable cations were observed in hectorite. Lead tended to occupy the one which corresponds to the −8 ppm peak on the 23Na MAS NMR spectrum. The behaviour of the exchangeable cations in the interlayer sites was similar in all the clay minerals studied.