11B Nuclear Magnetic Resonance Research Articles

The effect of iodine on the local environment of network‐forming elements in aluminoborosilicate glasses: An NMR study

AbstractKnowledge of the structural organization of nuclear waste glasses at the atomic scale is the basis for further studies of macroscopic properties (e.g., fracture toughness, chemical durability, and leaching rate). Recent studies have focused on the iodine dissolution mechanism in oxide‐based glasses synthesized under high‐pressure conditions, but there is still a lack of key information on the extent of the modifications caused by iodine entering the glass network. We therefore decided to conduct an in‐depth study by nuclear magnetic resonance on two series of aluminoborosilicate glasses synthetized under high pressure conditions and doped with either I2 or I2O5. The obtained 11B, 23Na, and 27Al nuclear magnetic resonance (NMR) spectra were fitted and correlated with the iodine content in order to find possible relationships with the local environment change for the probed cations. These data showed that iodine has no effect on the coordination of aluminum and very little effects on that of boron. In contrast, we found an expected relationship of the I content with the 23Na NMR parameters. In comparison with previous studies on the non‐bridging oxygen (NBO) distribution in aluminoborosilicate, we suggest that Na+ is mainly scavenged from silica tetrahedra with one or two NBO ( or ) as no boron planar triangles with one NBO are expected for such compositions. From those information, we establish a model for iodine dissolution in nuclear waste glass that is consistent with previous studies.

11B NMR of the Morphological Evolution of Traditional Chinese Medicine Borax.

This article applies nuclear magnetic resonance technology to the study of boron-containing traditional Chinese medicine, in order to explore the morphological evolution of boron elements in traditional Chinese medicine. Borax is a traditional Chinese medicine with anti-corrosion, anti-inflammatory, antibacterial, and anticonvulsant effects. It is made by boiling, removing stones, and drying borax minerals like borate salts. This article introduces an 11B nuclear magnetic resonance method for identifying and characterizing boron-containing compounds in TCM. We applied this technology to borax aqueous solutions in different chemical environments and found that with boron mixed in the form of SP2 hybridization in equilateral triangles and SP3 hybridization in equilateral tetrahedra, the pH changes in alkaline environments significantly affected the ratio of the two. At the same time, it was found that in addition to the raw material peak, boron signals of other boron-containing compounds were also detected in 20 commercially available boron-containing TCM preparations. These new boron-containing compounds may be true pharmaceutical active ingredients, and adding them directly to the formula can improve quality and safety. This article describes the detection of 11B NMR in boron-containing traditional Chinese medicine preparations. It is simple, non-destructive, and can provide chemical fingerprint studies for boron-containing traditional Chinese medicine.

Pd-Catalyzed Suzuki-Miyaura Cross-Coupling Reaction in Glycerol Using KOH as Base and Glycerol-Triethanolamine Deep Eutectic Solvent under Inorganic Base‑Free Conditions

Glycerol and glycerol-triethanolamine deep eutectic solvent are both environmentally benign, cost-effective, and practical solvents for the Pd-catalyzed Suzuki-Miyaura cross-coupling of aryl halides with arylboronic acids. Utilizing KOH as base, the reaction in glycerol proceeded smoothly with low catalyst loadings (up to 0.5 mol% of PdCl2(PPh3)2) providing excellent yields (up to 99%) of the cross-coupling products, which can be readily extracted with hexane. However, the recyclability of the glycerol medium containing the catalyst is limited to a few cycles. Furthermore, it was explored the use of chlorodiphenylphosphine as a pre-ligand. Although glycerol phosphinite was not generated in situ, PPh2Cl proved to be an excellent pre-ligand, yielding the coupling product with a 98% yield. Compared to glycerol, glycerol-triethanolamine deep eutectic solvent (TEOA:G DES) proves to be a superior solvent for the cross-coupling reaction. In addition, the presence of amine group in the solvent allowed to obtain an inorganic base-free cross-coupling protocol. Aryl bromides and aryl boronic acids containing both electron releasing and attracting functional groups can be coupled without requiring the addition of any further base, affording the biphenyl products in moderate to good yields. The cross-coupling products can be easily isolated by extraction with hexane. Moreover, we observed the formation of triethanolamine phenylboronate during the reaction. The triethanolamine boronate was subsequently synthesized through the condensation of phenylboronic acid with triethanolamine and fully characterized. 11B nuclear magnetic resonance (NMR) spectroscopy confirmed the coordination of the nitrogen to the boron atom of the triethanolamine boronate.

Fractal-like kinetics for enhanced boron adsorption on heterogeneous magnetic composite surfaces

Co-precipitated 14 nm γ-Fe2O3 and 35 nm MgO nanoparticles (NPs) decorated on zeolite 5 A (Z5A) templates were systematically studied. 57Fe Mössbauer and transmission electron microscopy data indicated a broad particle size distribution. The spinel structure of γ-Fe2O3 is strongly affected by size effects (particles smaller than 10 nm in size have an octahedral/tetrahedral iron site ratio of 7/3 instead of 5/3 found in bulk). 27Al nuclear magnetic resonance (NMR) showed the formation of octahedral Al species after boric acid reaction with MgO NPs. 11B NMR spectra indicated adsorption of B on the MgO/Z5A surface, whereas B adsorption in the pure Z5A framework is absent. Adsorption isotherms and kinetic studies of the nanohybrids showed that the B-rich species adsorption is described by Freundlich and fractal-like models, respectively. B adsorption occurs dominantly by the MgO fraction. The nanohybrids presented a good B removal efficiency when compared with other materials reported in literature.

Cation field‐strength effects on ion irradiation‐induced mechanical property changes of borosilicate glass structures

AbstractWe examine the impact of the glass network‐modifier cation field strength (CFS) on ion irradiation‐induced mechanical property changes in borosilicate (BS) glasses for the ternary M2O–B2O3–SiO2 systems with M = {Na, K, Rb} and the quaternary [0.5M(2)O–0.5Na2O]–B2O3–SiO2 systems with M = {Li, Na, K, Rb Mg, Ca, Sr, Ba}. 11B nuclear magnetic resonance (NMR) experiments on the as‐prepared BS glasses yielded the fractional population of four‐coordinated B species (B[4]) out of all {B[3], B[4]} groups in the glass network, along with the fraction of B[4]–O–Si linkages out of all B[4]–O–Si/B bonds. Both parameters correlated linearly with the (average) CFS of the M+ and/or {M(2)+, Na+} cations. Both the nanoindentation‐derived hardness and Young's modulus values of the glasses reduced upon their irradiation by Si2+ ions, with the property deterioration decreasing linearly with increasing Mz+ CFS, that is, for higher Mz+⋅⋅⋅O interaction strength. The irradiation damage of the glass network also increased linearly with the fraction of B[4]–O–Si linkages, which are the second weakest in the structure after the Mz+⋅⋅⋅O bonds. Our results underscore the advantages of employing BS glasses with high‐CFS cations for enhancing the radiation resistance for nuclear waste storage.

1,2-Diphenyl-o-carborane and Its Chromium Derivatives: Synthesis, Characterization, X-ray Structural Studies, and Biological Evaluations.

The objective of this study is to design and synthesize substituted η6-chromium(0) tricarbonyl metal complexes carrying o-carborane units as potential boron neutron capture therapy (BNCT) agents. In this study, 1,2-diphenyl-o-carborane (1) units were used as starting materials to generate biologically active species. We investigated how the structural changes of 1 substituted with chromium(0) tricarbonyl affect the biological properties, and 1-(Phenyl-η6-chromium(0) tricarbonyl)-2-phenyl-o-carborane (2) and 1,2-bis(phenyl-η6-chromium(0) tricarbonyl)-o-carborane (3) species were produced in moderate yields. The molecular structures of compounds 1-3 were identified and established by infrared (IR); 1H, 11B, and 13C nuclear magnetic resonance (NMR) and X-ray crystallography analyses. Crystal structures of 1,2-diphenyl-o-carborane and the corresponding chromium complexes 1, 2, and 3 were obtained. In an in vitro study using B16 and CT26 cancer cells containing the triphenyl-o-carboranyl chromium(0) complexes Ph3C2BCr2 and Ph3C2BCr3, which we reported previously, compounds 2 and 3 accumulated at higher levels than compounds Ph3C2BCr2 and Ph3C2BCr3. However, the phenylated o-carboranyl chromium complexes have been found to be more cytotoxic than p-boronophenylalanine (BPA).

Proximate deconfined quantum critical point in SrCu2(BO3)2.

The deconfined quantum critical point (DQCP) represents a paradigm shift in quantum matter studies, presenting a "beyond Landau" scenario for order-order transitions. Its experimental realization, however, has remained elusive. Using high-pressure 11B nuclear magnetic resonance measurements on the quantum magnet SrCu2(BO3)2, we here demonstrate a magnetic field-induced plaquette singlet to antiferromagnetic transition above 1.8 gigapascals at a notably low temperature, Tc ≃ 0.07 kelvin. First-order signatures of the transition weaken with increasing pressure, and we observe quantum critical scaling at the highest pressure, 2.4 gigapascals. Supported by model calculations, we suggest that these observations can be explained by a proximate DQCP inducing critical quantum fluctuations and emergent O(3) symmetry of the order parameters. Our findings offer a concrete experimental platform for investigation of the DQCP.

Dynamical properties of the magnesium borohydride – ethylenediamine compound Mg(en)1.2(BH4)2: A nuclear magnetic resonance study

The magnesium borohydride – ethylenediamine (en) compound Mg(en)1.2(BH4)2 exhibits high Mg-ion conductivity above room temperature. To study the dynamical properties of this compound and its partially deuterium-substituted counterpart, we have measured the 1H, 2D, and 11B nuclear magnetic resonance (NMR) spectra and spin-lattice relaxation rates over a wide temperature range (6–324 K). Our measurements have revealed a coexistence of four types of BH4 reorientational jump processes with different activation energies. For the fastest of these processes characterized by the activation energy of 47(3) meV, the unusually high reorientational mobility is retained down to low temperatures, so that the corresponding H jump rate is of the order of 108 s−1 near 70 K. The presence of fast reorientational motion of [BH4]− anions in Mg(en)1.2(BH4)2 supports the idea that anion reorientations may facilitate the cation diffusion. In the studied temperature range, we have not found any distinct signs of localized motion of the ethylenediamine molecules or their fragments at the NMR frequency scale.

Local Geometry of Tetrahedrally Coordinated Boron Correlates with 11B NMR Chemical Shifts in Borosilicate Minerals

Chemical shifts from the 11B nuclear magnetic resonance (NMR) spectra of crystalline borosilicate minerals with highly ordered, tetrahedrally coordinated boron atoms (B) linearly correlate with the local geometric parameters related to the B–O–T angles (T denotes a tetrahedrally coordinated atom) obtained from single-crystal X-ray diffraction. The correlations between the 11B NMR chemical shifts and structural parameters are similar in functional form to the well-known correlations of 29Si and 27Al NMR chemical shifts with structural features of silicates and aluminosilicates, respectively. These correlations enable the use of 11B NMR chemical shifts to elucidate the local geometry of tetrahedrally coordinated B and aid in establishing B ordering among the crystallographic T-sites within crystalline borosilicates.

An investigation of Al2O3 induced variations in the structural parameters in strontium borosilicate glasses using solid state NMR.

The physical properties of oxide glasses are crucially dependent on the atomistic structural speciation. In this study, we investigate the variation in the local ordering in the glass network of strontium borosilicate glasses (34.82 SrO, 51.84 B2O3, 13.34 SiO2 in mol%) with a progressive substitution of B2O3 by Al2O3 and estimate the structural parameters: the oxygen packing fraction, and the average network coordination number. The coordination of the network forming cations at various glass compositions is determined using 11B, 27Al, and 29Si solid-state nuclear magnetic resonance (SSNMR). The SSNMR reveals that at the higher substitution of B2O3 by Al2O3 in the glass composition, the coordination network of Al3+ exists predominantly in the 4 coordinated state, the network forming B3+ cations transform from a tetrahedral BO4 to a trigonal BO3 structure, and the Q4 form of silicates is dominant. The average coordination number and the oxygen packing fraction were calculated using the parameters obtained from the SSNMR results, and it is observed that the average coordination number decreases, and the oxygen packing fraction increases on incorporating Al. It is interesting to note that some of the thermophysical properties of these compositions closely follow the pattern shown by the average coordination number and the oxygen packing fraction.

Novel red-emitting Ca2LiScB4O10: Sm3+ phosphor for WLED: Photoluminescence, thermal stability, crystal structure, Judd-Ofelt parameters and energy band gap studies

In this paper, a novel red-emission Ca2LiScB4O10: Sm3+ phosphor system has been synthesized by a high-temperature solid-state reaction method. 50–100 nm well-distributed monoclinic Ca2LiScB4O10: Sm3+ (space group of P21/n) was confirmed by Transmission electron microscopy and SAED patterns. Rietveld refinement PXRD pattern revealed that the doping of different amounts of Sm3+ ions expanded the lattice constants/volume and shifted the most intense diffraction peaks to a larger angle side with shoulders. The changes in coordination groups and crystal structure of Ca2LiScB4O10 have been observed from the Fourier transform infrared spectra, the 11B nuclear magnetic resonance, and O1s and B1s X-ray photoelectron spectroscopy. The increase of Sm3+ doping amounts decreased the energy band gap which matched well with the density functional theory simulation. The studies on the crystal structure and Rietveld refinement indicated that the Sm3+ occupied both the Ca2+ and Sc2+ sites. The photoluminescence performances such as the excitation/emission spectra, CIE diagram, decay lifetime, and thermal stability have been systematically investigated. The photoluminescence behaviors have been explained by Judd-Ofelt cross-section, branching ratio, color temperature, quantum efficiency, and lifetime. The energy level of Sm3+ and the emission and thermal quenching mechanism were discussed. 0.7%Sm phosphor exhibited significant pure and strong reddish emission at 600 nm and this phosphor is promising for WLED device application.

Photocatalytic phenol oxidation over ball milled hexagonal boron nitride

Due to their high toxicity, even a small amount of phenols entering the surrounding aquatic environment poses a serious danger to all living beings. To address this important problem, commercial micron-sized h-BN powder was ball milled at 450, 600 and 750 rpm, surface-functionalized with hydroxyl and amino groups by sonication, and characterized as a promising photocatalyst. The samples were studied by X-Ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, 11B nuclear magnetic resonance, scanning and transmission electron microscopy, diffuse reflectance ultraviolet–visible spectroscopy and photoluminescence spectroscopy. At all rates of mechanical processing without the use of auxiliary reagents, exfoliation of h-BN flakes was achieved. An increase in the ball milling rate led to a decrease in crystallinity and structure refinement, which was accompanied by the formation of a large number of dislocations and nanocrystallites 2–5 nm in size. Upon subsequent sonication, the BN powder underwent partial oxidation and functionalization with O(H) groups. The observed increase in the photocatalytic activity of ball-milled h-BN particles in the phenol oxidation reaction is explained by an increase in the 254 nm UV-light absorption, a decrease in the rate of electron-hole recombination, and an increase in the formation rate of OH radicals. Our results clearly show the promise of ball milled commercial micron-sized h-BN powder as a photocatalyst in the phenol oxidation reaction.

Interaction of the anion [2-B<sub>10</sub>H<sub>9</sub>O(CH<sub>2</sub>)<sub>4</sub>O]− with secondary amines

Objectives. One of the most promising methods of treating malignant tumors is 10B-neutron capture therapy. While compounds based on cluster boron anions [BnHn]2− (n = 10, 12) are often used as boron-containing agents due to the very high specific concentration of boron atoms per particle, the use of such compounds is associated with the need to develop new methods for the functionalization of boron clusters associated with the production of boron-containing derivatives containing biologically active functional groups. One of the most convenient methods of modification of [BnHn]2− (n = 10, 12) anions is the interaction of their derivatives containing cyclic oxonium-type substituents with negatively charged or neutral nucleophilic reagents. The disclosure of substituents of this type leads to the formation of closo-borates with functional groups separated from the cluster by an alkoxyl spacer chain. The purpose of this study is to develop methods for the synthesis of derivatives of the closo-decaborate anion [B10H10]2− with pendant nitrogen-containing groups.Methods. The general control of the reactions of the disclosure of cyclic substituents was carried out on the basis of 11B nuclear magnetic resonance (NMR) spectroscopy data. The structure of the obtained derivatives, including the nature of the attached functional groups, was determined using 1H, 13C attached proton test (APT) NMR and infrared (IR) spectroscopy data. The molecular weight of the synthesized compounds was confirmed by electrospray ionization mass-spectrometry (ESI–MS).Results. The interaction of the anion [2-B10H9O(CH2)4O]− with secondary amines (dimethylamine, dipropylamine, diallylamine, dibutylamine, diisobutylamine, morpholine, di-sec-butylamine) in an ethanol environment is investigated. As a result of the reactions, a cyclic substituent is shown to expand with the addition of a nucleophilic reagent. Seven new derivatives of the closodecaborate anion with pendant nitrogen-containing groups have been synthesized.Conclusions. A developed method for obtaining closo-decaborates with ammonium groups separated from the boron cluster by an alkoxyl spacer group is presented. It is shown that the use of amines of various structures does not fundamentally affect the course of the reactions, allowing the composition and structure of the target derivatives to be effectively regulated. The resulting compounds can be involved in further modification reactions due to a reactive pendant group, as well as being suitable for use as effective polydentate ligands. Closo-decaborates with pendant nitrogen-containing groups and their derivatives are of considerable interest in the synthesis of compounds for use in 10B-neutron capture therapy of malignant tumors.

Liquid fragility maximum in lithium borate glass‐forming melts related to the local structure

AbstractThe structure of liquid lithium pyroborate, Li4B2O5 (J = Li/B = 2), has been measured over a wide temperature range by high‐energy X‐ray diffraction, and compared to that of its glass and borate liquids of other compositions. The results indicate a gradual increase in tetrahedral boron fraction from 3(1)% to 6(1)% during cooling from T = 1271(15) to 721(8) K, consistent with the larger N4 = 10(1)% found for the glass, and literature 11B nuclear magnetic resonance measurements. van't Hoff analysis based on a simple boron isomerization reaction BØ3O2– ⇌ BØO22– yields ΔH = 13(1) kJ mol–1 and ΔS = 40(1) J mol–1 K–1 for the boron coordination change from 4 to 3, which are, respectively, smaller and larger than found for singly charged isomers for J ≤ 1. With these, we extend our model for N4(J, T), nonbridging oxygen fraction fnbr(J, T), configurational heat capacity , and entropy Sconf(J, T) contributions up to J = 3. A maximum is revealed in at J = 1, and shown semi‐quantitatively to lead to a corresponding maximum in fragility contribution, akin to that observed in the total fragilities by temperature‐modulated differential scanning calorimetry. Lithium is bound to 4.6(2) oxygen in the pyroborate liquid, with 2.7(1) bonds centered around 1.946(8) Å and 1.9(1) around 2.42(1) Å. In the glass, nLiO = 5.4(4), the increase being due to an increase in the number of short Li–O bonds.

Incommensurate Magnetic Order in Sm3BWO9 with Distorted Kagome Lattice

We investigate the magnetic ground state of Sm3BWO9 with a distorted kagome lattice. A magnetic phase transition is identified at T N = 0.75 K from the temperature dependence of specific heat. From 11B nuclear magnetic resonance measurements, an incommensurate magnetic order is shown by the double-horn type spectra under a c-axis magnetic field, and absence of line splitting is observed for field oriented within the ab-plane, indicating the incommensurate modulation of the internal field strictly along c-axis. From the spin dynamics, the critical slowing-down behavior is observed in the temperature dependence of 1/T 1 with μ 0 H⊥c-axis, which is completely absent in the case with μ 0 H||c-axis. Based on the local symmetry of 11B sites, we analyze the hyperfine coupling tensors and propose two constraints on the possible magnetic structure. The single ion anisotropy should play an important role in determination of contrasting ground states of Sm3BWO9 and Pr3BWO9.

Boronate derivatives of damnacanthal: Synthesis, characterization, optical properties and theoretical calculations

The natural anthraquinone Damnacanthal (1) was isolated from the roots of Morinda panamensis and used as a building block in the construction of five fluorescent boronate derivatives (4a–4e). The novel compounds were obtained in moderate yields by the condensation of 1, anthranilic acid (2) and diverse phenylboronic acids (3a–3e) in acetonitrile. Boronate derivatives were fully characterized by 1H, 13C, 11B and 2D nuclear magnetic resonance (NMR) spectroscopy, Fourier-transform infrared spectroscopy (FT-IR), ultraviolet–visible spectroscopy (UV–vis), and high-resolution mass spectrometry (HR-MS). The photophysical properties were evaluated in tetrahydrofuran revealing that the optical band gap (Egopt) values increase from 2.54 eV for 4a to 2.65 eV for 4d. The maximum emission wavelength and fluorescence quantum yield (ΦF) of the boron complexes were found to be sensitive to the substituents on the phenyl group attached to the boron atom. The resulting derivatives 4a–4c presented emission bands at approximately 522 nm (ΦF = 0.41, 0.13 and 0.37%, respectively); while derivatives 4d and 4e presented broad emission bands with maxima at 676 nm (ΦF = 6.27%) and 614 nm (ΦF = 0.78%), respectively. The molecular geometry, electronic properties and intramolecular non-covalent interactions of the new molecules were evaluated using density functional theory (DFT) and quantum theory of atoms in molecules (QTAIM) methods. The value of the energy gap between the HOMO and LUMO increases from 2.89 eV for 4b, 2.96 eV for 4c, 3.04 eV for 4e, 3.08 eV for 4a to 3.32 eV for 4d. Furthermore, compound 4d showed a higher rotational energy barrier (3.33 kcal/mol) at the dihedral angle N1/B1/C24/C25 than its analogs, due to the F∙∙∙π and F∙∙∙O interactions.

A new self‐consistent empirical potential model for multicomponent borate and borosilicate glasses

AbstractA new self‐consistent empirical potential model based on the BMP potential [Bertani et al., Phys. Rev. Mat. 5 (2021) 045602] has been developed for the simulation of multicomponent borate and borosilicate glasses. We exploited the Bayesian optimization approach to create a set of parameters for the B–O interaction, which depends on the glass composition, and in particular on the R = ([A2O]+[AEO])/[B2O3] (A = alkaline and AE alkaline‐earth ions) and K = [SiO2]/[B2O3] ratios. The obtained force field (FF) has been applied to several borate and borosilicate glass series containing, as modifier oxide, Na2O, Li2O, CaO, and MgO and tested on experimental data, such as the fraction of BO4 (N4), density, non‐bridging oxygen speciation, neutron diffraction spectra, 11B, 29Si, and 17O magic angle spinning nuclear magnetic resonance. A comparison with other interatomic potentials available in literature has also been performed. The results show that the FF reproduces well almost all the abovementioned properties, showing excellent agreement with experimental data in a wide range of compositions.

Catalytic Effect of Ionic Liquid Induced H2-Release from Morpholine Borane Complex: An Efficient Hydrogen Storage Carrier

The demand for effective and secure chemical hydrogen storage systems impedes hydrogen’s usage as an alternative energy carrier. This work reports the use of morpholine borane (MB) as a novel, efficient, and widely viable chemical hydrogen storage material for mobile applications. Herein, for the first time, hydrogen generation from the thermolytic dehydrogenation of MB in the presence of ionic liquid (IL) media is reported. Initially, the COSMO-SAC model was utilized to determine the most appropriate solvent. [Bmim][HSO4] proved to be an excellent catalytic solvent media with maximum solubility in the morpholine borane complex. Thermal dehydrogenation experiments were conducted separately on solid-state and MB-IL systems at 60 and 80 °C in a vacuum-sealed experimental setup. After a prolonged heating period, the solid-state dehydrogenation of the MB complex released 0.62 equiv of hydrogen, whereas the dehydrogenation of the MB-IL system at 60 and 80 °C released 1.75 and 1.46 equiv of hydrogen in a shorter time. The residue products were characterized using 1H and 11B nuclear magnetic resonance (NMR). 1H NMR validated IL’s activity as a catalytic solvent without affecting its structural identity, whereas 11B NMR helped establish an intra- and intermolecular dehydrogenation mechanism connected with MB. As confirmed by the density functional theory-based transition state calculations, the intramolecular dehydrogenation pathway results in a dehydrocoupled product with minimal energy required for the dehydrogenation reaction.

Mixing nitrogen-containing compounds for synthesis of porous boron nitride for improved porosity, surface functionality, and solid base catalytic activity

Porous boron nitride was synthesized using boric acid with urea and/or hexamethylenetetramine (HMTA) via pyrolysis method. X-ray diffraction and Fourier transform infrared measurements indicated that the synthesized boron nitride has a turbostratic structure with both amino and hydroxyl group on the surface. The synthesis using a mixture of two nitrogen-containing precursors was found to not only significantly increase the porosity, but also improve the surface functionality. X-ray photoelectron spectroscopy and B K-edge and O K-edge X-ray absorption fine structure measurements revealed that the proportion of amino and hydroxyl groups on the surface increased with increasing concentration of HMTA during synthesis. Solid-state 11B nuclear magnetic resonance spectroscopy indicated that all samples contained trigonal B-N, trigonal B-O and tetrahedral B-O sites, and that samples prepared with high concentrations of HMTA had less tetrahedral B-O sites, suppressing the formation of BOx species as byproducts. Solid base catalytic activity was evaluated through Knoevenagel condensation, and the catalytic performance was significantly improved by synthesizing boron nitride catalyst using a mixture of the two nitrogen-containing precursors. The enhancement of the activity was influenced by the development of the pore structure as well as the emergence of functional groups on the surface.

Structural dependence of crystallization in phosphorus‐containing sodium aluminoborosilicate glasses

AbstractThe article reports on the structural dependence of crystallization in Na2O–Al2O3–B2O3–P2O5–SiO2‐based glasses over a broad compositional space. The structure of melt‐quenched glasses has been investigated using 11B, 27Al, 29Si, and 31P magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy, while the crystallization behavior has been followed using X‐ray diffraction and scanning electron microscopy combined with energy dispersive spectroscopy. In general, the integration of phosphate into the sodium aluminoborosilicate network is mainly accomplished via the formation of Al–O–P and B–O–P linkages with the possibility of formation of Si–O–P linkages playing only a minor role. In terms of crystallization, at low concentrations (≤5 mol.%), P2O5 promotes the crystallization of nepheline (NaAlSiO4), while at higher concentrations (≥10 mol.%), it tends to suppress (completely or incompletely depending on the glass chemistry) the crystallization in glasses. When correlating the structure of glasses with their crystallization behavior, the MAS NMR results highlight the importance of the substitution/replacement of Si–O–Al linkages by Al–O–P, Si–O–B, and B–O–P linkages in the suppression of nepheline crystallization in glasses. The results have been discussed in the context of (1) the problem of nepheline crystallization in Hanford high‐level waste glasses and (2) designing vitreous waste forms for the immobilization of phosphate‐rich dehalogenated Echem salt waste.