Spinning Nuclear Magnetic Resonance Spectroscopy Research Articles

Effect of zeolite calcination temperature on the carbonation degree and strength of steel slag compacts

Steel slag partially substituted with zeolite (SZ) is beneficial for further improving the compressive strength and carbonation degree, after a combined curing (hydration and carbonation) process, owing to the pozzolanic reaction. In this study, the effect of clinoptilolite-type zeolite calcinated at different calcination temperatures (200–800 ℃) to modify the degree of the pozzolanic reaction is investigated. Moreover, the characteristics of SZ specimens after combined curing are also investigated. Additionally, the degree of the pozzolanic reaction and its mechanism in CHZ (Ca(OH)2 mixed with calcinated zeolite after 1 day (1d) of hydration) specimens are clarified and compared by various microscopy techniques. Compressive strength results revealed that the optimum calcination temperature was 800 ℃. The compressive strength and carbonation degree of CSZ5-800 (steel slag specimen containing calcined zeolite (800 ℃) after 1d of hydration followed by 2 h of carbonation curing) improved by 23.2 and 13.8 %, respectively, compared with that of the reference CSZ5-25. The porosity of CSZ5-800 was 30.8 and 21.9 % higher than that of CSZ0-25and CSZ5-25, respectively. New minerals AFmc and C-S-H gel were detected by X-ray diffraction (XRD) and mass angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy in CHZ specimens. Notably, the C-S-H gel and AFmc content in CHZ-800 were 7 and 57.6 % higher than that of CHZ-25, respectively.

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.

Adsorption of copper ions in water by adipic dihydrazide-modified kapok fibers

Abstract Kapok fibers (Ceiba pentandra) were modified for the removal of copper ions from aqueous solutions through adsorption. In this fast and facile method, the polysaccharide-like groups of kapok were oxidized with potassium periodate. The novel modification is the loading of the fibers with adipic dihydrazide (ADH) which contain nitrogen and oxygen atoms for heavy metal ion binding. Adsorption experiments have been carried out and analyzed via atom absorption spectroscopy and ultraviolet/visible spectroscopy. In preliminary adsorption experiments, different kapok-based materials have been analyzed on their adsorption capacity and removal efficiency via atom absorption spectroscopy. ADH-modified fibers showed the best results and an increase of copper removal efficiency by 30% in comparison to untreated kapok fibers and superior adsorption capacity compared to kapok fibers loaded with oxalic dihydrazide (ODH). Moreover, the impact of initial concentration and contact time on the adsorption capacity and on the removal efficiency values of the ADH-modified kapok fibers has been studied. Another comparison of the ADH-modified fibers with raw kapok which was cleaned with Milli-Q water, dichloromethane and ethylene glycol showed that the new adsorbents are best suited for copper solutions with concentration values of under 10 mg/L. The heavy metal adsorption experiments were analyzed through both isotherm models Langmuir and Freundlich. The Langmuir model is found to be a suitable model for copper ions. The value of the maximum adsorption capacity is 4.120 mg/g. The ADH-modified kapok fibers were characterized with attenuated total reflection infrared (ATR-IR) spectroscopy, magic-angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopy and scanning electron microscopy (SEM).

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.

High-Resolution Magic-Angle Spinning NMR Spectroscopy for Evaluation of Cell Shielding by Virucidal Composites Based on Biogenic Silver Nanoparticles, Flexible Cellulose Nanofibers and Graphene Oxide.

Antiviral and non-toxic effects of silver nanoparticles onto in vitro cells infected with coronavirus were evaluated in this study using High-Resolution Magic-Angle Spinning Nuclear Magnetic Resonance (HR-MAS NMR) spectroscopy. Silver nanoparticles were designed and synthesized using an orange flavonoid—hesperetin (HST)—for reduction of silver(I) and stabilization of as obtained nanoparticles. The bio-inspired process is a simple, clean, and sustainable way to synthesize biogenic silver nanoparticles (AgNP@HST) with diameters of ∼20 nm and low zeta potential (−40 mV), with great colloidal stability monitored for 2 years. The nanoparticles were used for the fabrication of two types of antiviral materials: colloids (AgNP@HST spray) and 3D flexible nanostructured composites. The composites, decorated with AgNP@HST (0.05 mmol L−1), were made using cellulose nanofibers (CNF) obtained from orange peel and graphene oxide (GO), being denominated CNF@GO@AgNP@HST. Both materials showed high virucidal activity against coronaviruses in cell infection in vitro models and successfully inhibited the viral activity in cells. HR-MAS 1H-NMR technique was used for determining nanomaterials’ effects on living cells and their influences on metabolic pathways, as well as to study viral effects on cells. It was proven that none of the manufactured materials showed toxicity towards the intact cells used. Furthermore, viral infection was reverted when cells, infected with the coronavirus, were treated using the as-fabricated nanomaterials. These significant results open possibilities for antiviral application of 3D flexible nanostructured composite such as packaging papers and filters for facial masks, while the colloidal AgNP@HST spray can be used for disinfecting surfaces, as well as a nasal, mouth, and eye spray.

Solid-state NMR spectroscopy measurement of fluoride reaction by bovine enamel and dentin treated with silver diammine fluoride

ObjectivesThe aim of this study was to investigate the formation of fluoride compounds in bovine enamel and dentin treated with silver diammine fluoride (SDF) using 19F and 31P solid-state magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy. MethodsEnamel and dentin powder, obtained from bovine teeth, were treated with 38% SDF for four minutes and then washed thoroughly with Milli-Q water. The dehydrated SDF-treated samples were then examined. 19F solid-state MAS NMR spectra were acquired and 1H–31P cross-polarization (CP) experiments were performed on SDF-treated enamel and dentin powder. The surfaces of SDF-treated enamel and dentin blocks were observed by Scanning Electron Microscope (SEM). Results19F MAS NMR detected a more pronounced signal intensity for the dentin sample than the enamel, indicating an increased reactivity of SDF for dentin, compared with enamel. 19F NMR spectra for the SDF-treated samples showed fluorhydroxyapatite (FHAp), and other fluoride compounds such as CaF2 and the fluoride-substituted carbonate. The 1H–31P CP intensities of prominent peaks were lower for the SDF-treated samples than the non-treated sample, indicating that the F- ion replaced the OH- ion in the lattice tunnel. SEM observations on the SDF-treated samples showed pronounced multiple precipitation and particles in dentin compared with enamel. SignificanceThe solid-state MAS NMR revealed the reaction of fluoride on enamel and dentin and the identification of fluoride compounds. In particular, the formation of FHAp indicates that SDF is effective in reducing the risk of tooth decay.

Evaluation of Zeolite Acidity by 31P MAS NMR Spectroscopy of Adsorbed Phosphine Oxides: Quantitative or Not?

31P magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy of adsorbed alkyl-substituted phosphine oxides has witnessed tremendous progress during the last years and has become one of the most informative and sensitive methods of zeolite acidity investigation. However, quantitative evaluation of the number of sites is still a challenge. This study clarifies the main origin of errors occurring during NMR experiments, introduces the appropriate standards (both internal and external), and determines the relaxation parameters and the conditions for the acquisition and integration of spectra. As a result, a methodology for the quantitative measurement of the content of Brønsted and Lewis sites and the amount of internal and external silanol groups is established. The application of probe molecules of different sizes (namely, trimethylphosphine oxide (TMPO), tri-n-butylphosphine oxide (TBPO), and tri-n-octylphosphine oxide (TOPO)) is shown to be a good tool for distinguishing between the active sites inside the zeolite pores, mesopores, and on the outer crystal surface. The methodology proposed is verified on BEA zeolites different in composition, texture, and morphology.

Ultrafast Nanocrystallization of BaF2 in Oxyfluoride Glasses with Crystal-like Nanostructures: Implications for Upconversion Fiber Devices

Transparent glass–ceramic fibers containing fluoride nanocrystals are attracting attention as upconversion devices. In this paper, a material design is proposed that eliminates the need for heat treatment processes. The impact of short- to medium-range structures on the crystallization of glasses was investigated to enable nanocrystallization in the quenching process via ultrafast nucleation. In this study, the short- to medium-range structures of (33.3 – x/3)BaF2–xZnO–(66.7 – 2x/3)B2O3 glasses were investigated by 11B- and 19F-magic-angle spinning nuclear magnetic resonance spectroscopy, molecular dynamics simulations, and the high-energy synchrotron X-ray diffraction. After heat treatment, glasses with x > 40 formed BaF2 nanocrystals with a diameter of ∼5 nm and a small particle size distribution (<1 nm). Based on the high-energy synchrotron X-ray diffraction, the critical size of the nuclei was estimated to be 4 nm, which was similar to the size of the precipitated crystals. Obvious selectivity in the binding was observed: F– preferred Ba2+ and O2– preferred B3+, whereas Zn2+ was bound to both anions. The binding selectivity caused a bicontinuous structure of oxide and fluoride domains, and the fluoride-related structure factors and bond distance were very similar to the peak positions of the precipitated crystals. Er3+-doped glasses with x > 40 showed upconversion luminescence with a spectrum similar to that of BaF2. These results suggested the pre-existence of a crystal-like structure with a composition, density, and ordering similar to those of the precipitated crystals. Moreover, glass with the modified composition was successfully crystallized during press-quenching of the melt and the fiber drawing process. These results could facilitate the production of photonic components such as nanocrystallized glass fibers and microspheres for upconversion lasers as well as a wide variety of glass–ceramic products.

A Simple and Feasible Quantification of Metabolites in the Human Follicular Fluid Using 1H HR-MAS NMR Spectroscopy

This study presents a reliable method for the quantification of metabolite concentrations in follicular fluid with the high-resolution magic angle spinning nuclear magnetic resonance (HR-MAS NMR) spectroscopy and the ERETIC2 (Electronic REference To access In vivo Concentrations) based on PULCON (pulse length based concentration determination) principle. The positive effect of the HR-MAS probe technology on spectral quality and its ability to perform analyses with very low sample amounts were the most important factors of proposing this method. In evaluating the performance of the proposed method, standard creatine solutions in different concentrations containing DSS (2,2-dimethyl-2-silapentane-5-sulfonate sodium salt) as an internal reference standard were analyzed using different pulse programs (cpmgpr1d and zg30). The results obtained with the ERETIC2 were compared with the classical internal standard NMR quantification method (DSS method). The relative standard deviation (RSD) values for ERETIC2 were in the range of 0.3% - 5.7% and recovery values were calculated as minimum 90.3%, while RSD values for DSS method were in the range of 0.1% - 3.1% and recovery values were minimum 97.0%. Besides, it was observed that the metabolite concentration values calculated using the ERETIC2 procedure of follicular fluid samples obtained from the women with endometriosis and healthy controls were compatible with the values those obtained using different methodologies. The obtained results showed that the proposed quantification method based on the HR-MAS spectroscopy can easily be used in biological fluids and therefore it can be utilized as a good alternative to the internal standard method considering its accuracy and precision.

High-Entropy Polyanionic Lithium Superionic Conductors

High-entropy ceramics are attracting large interest because of their unique materials properties. Nevertheless, the effect of entropy on the lithium transport remains largely elusive. Here, we report, for the first time, about medium- and high-entropy polyanionic lithium superionic conductors crystallizing in the F–43m space group and adopting the so-called argyrodite structure. The Li6PS5[Cl0.33Br0.33I0.33], Li6P[S2.5Se2.5][Cl0.33Br0.33I0.33], and Li6.5[Ge0.5P0.5][S2.5Se2.5][Cl0.33Br0.33I0.33] materials were structurally characterized using complementary synchrotron and neutron scattering techniques in combination with 31P magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. We show that, in contrast to other high-entropy ceramics, an unequal distribution of elements over the respective crystallographic sites occurs in these materials. Using electrochemical impedance spectroscopy (EIS) and 7Li pulsed field gradient (PFG) NMR spectroscopy, we demonstrate that introducing entropy (compositional disorder) marginally affects the room-temperature ionic conductivity (∼10–3 S cm–1) but instead lowers the activation energy for conduction to 0.22 eV. Our results emphasize the possibility of increasing entropy in polyanionic materials, thereby opening up compositional space for the search of Li-ion conductors with unprecedented properties.

Synthesis and characterization of a polycarboxylate superplasticizer modified by sodium hypophosphite

AbstractA sodium hypophosphite (SHP) modified polycarboxylatesuperplasticizer (P‐PCE) was synthesized successfully and the synthesis parameters were optimized through orthogonal experiment. Gel permeation chromatography (GPC), X‐ray photoelectron spectroscopy (XPS), 31P magic spinning nuclear magnetic resonance (31P MAS NMR) spectroscopy and elemental analysis measurements were used to characterize the molecular structure of P‐PCE. Effects of P‐PCE on the dispersing performance of cement paste were systematically investigated via mini slump test. The results showed that P‐PCE exhibited superior dispersing performance, more retarding hydration effect and better sulfate and clay tolerance than conventional PCE (C‐PCE). Results showed that the maximum flow of cement paste could reach up to 305 mm, while that of the C‐PCE was 285 mm.The maximum variation of adsorption of P‐PCE was 9% and 15% in the presence of sulfate and clay, whereas that of C‐PCE was 15% and 25%, respectively, leading to better sulfate and clay tolerance. These significant advantages could be ascribed to the high anion density and high calcium complexing capacity induced by introducingphosphinate group and phosphonate group into the molecular structure of P‐PCE. The as‐synthesized P‐PCE can be used as a kind of high performance superplasticizer in concrete engineering.

Assessing Factors Controlling Structural Changes of Humic Acids in Soils Amended with Organic Materials to Improve Soil Functionality

Humic acids (HAs) regulate soil chemical reactivity and improve many soil functions. The amendment of soil with organic materials increases soil organic matter (SOM) content and promotes the formation of HAs. However, the effect of the type, frequency and duration of amendment, and pedoclimatic conditions on SOM transformation and HA structural changes remains unclear. Herein, four experimental field sites (S1–4) with short-to-long-term organic fertilisation schemes were used to assess the effects of such factors, i.e., S1: loamy sand amended once with farmyard manure (FYM), brown coal waste (BCW), and biochar (BIO) for 0.5 and 1.5 years; S2: silt loam amended once with BIO for 8 years; S3: loamy sand amended every 5 years with FYM for 94 years; and S4: clayey silt amended every 2 years with FYM for 116 years. All HAs were extracted and analysed for structural differences by elemental analysis (EA), attenuated total reflectance–Fourier transform infrared spectroscopy (ATR-FTIR), solid-state cross polarisation magic angle spinning nuclear magnetic resonance spectroscopy (CP/MAS 13C-NMR), and differential scanning calorimetry (DSC). Results from EA, FTIR, and NMR showed that the long-term samples from S3 (treatments, T9–T10) and S4 (T11–T12) had the greatest aromatic characteristics, which increased with FYM amendment (T10 and T12). These agreed with DSC data, which indicated lower aliphatic contents compared with other samples. Samples from S2 (T7–T8), with receded amendment effects, had less aromatic and greater aliphatic characteristics compared with the short-term samples, S1 (T1–T6). In S1, structural changes were limited, but aromaticity increased with BIO (T3 and T6) compared with corresponding FYM (T1 and T4) and BCW (T2 and T5) amendments due to inherently high aromatic groups in the former. Overall, the results showed that the site (due to differences in pedoclimatic conditions), field age of OM, and amendment frequency were the main factors that influenced HA structure, and hence SOM transformation. Regular, long-term organic amendment increases the aromatic characteristics of HAs, which can improve soil functionality, but short-term structural improvements are achievable only when amending material is rich in aromatic compounds.

Quantitative analysis of C-(K)-A-S-H-amount and hydrotalcite phase content in finely ground highly alkali-activated slag/silica fume blended cementitious material

For the development of CO2-reduced binders for structural engineering and for predicting their performance, knowledge of the amount formed in weight fractions of the reaction products is essential. This paper presents a method to specify the hydration products of an alkali-activated slag/silica fume blended cementitious material by weight. The 29Si and 27Al magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy to determine the C-A-S-H phases was coupled with energy dispersive analysis (EDX) technology to determine the bound K/Si ratio. Furthermore, the 27Al MAS NMR was used to define the amount of hydrotalcite. With the help of the developed model, the hydration phases of alkali-activated slag/silica fume blended cementitious material in dependency of the activator can be calculated. The results of the mass ratios deduced by NMR with coupled EDX was in agreement with the loss of ignition measured by thermogravimetric analysis (TGA). Consequently, the hydration products can be self-checked.

A Metabonomic View on Wilms Tumor by High-Resolution Magic-Angle Spinning Nuclear Magnetic Resonance Spectroscopy.

Pediatric cancer NMR-metabonomics might be a powerful tool to discover modified biochemical pathways in tumor development, improve cancer diagnosis, and, consequently, treatment. Wilms tumor (WT) is the most common kidney tumor in young children whose genetic and epigenetic abnormalities lead to cell metabolism alterations, but, so far, investigation of metabolic pathways in WT is scarce. We aimed to explore the high-resolution magic-angle spinning nuclear magnetic resonance (HR-MAS NMR) metabonomics of WT and normal kidney (NK) samples. For this study, 14 WT and 7 NK tissue samples were obtained from the same patients and analyzed. One-dimensional and two-dimensional HR-MAS NMR spectra were processed, and the one-dimensional NMR data were analyzed using chemometrics. Chemometrics enabled us to elucidate the most significant differences between the tumor and normal tissues and to discover intrinsic metabolite alterations in WT. The metabolic differences in WT tissues were revealed by a validated PLS-DA applied on HR-MAS T2-edited 1H-NMR and were assigned to 16 metabolites, such as lipids, glucose, and branched-chain amino acids (BCAAs), among others. The WT compared to NK samples showed 13 metabolites with increased concentrations and 3 metabolites with decreased concentrations. The relative BCAA concentrations were decreased in the WT while lipids, lactate, and glutamine/glutamate showed increased levels. Sixteen tissue metabolites distinguish the analyzed WT samples and point to altered glycolysis, glutaminolysis, TCA cycle, and lipid and BCAA metabolism in WT. Significant variation in the concentrations of metabolites, such as glutamine/glutamate, lipids, lactate, and BCAAs, was observed in WT and opened up a perspective for their further study and clinical validation.

Crystallochemical Characterizations, Raman Spectroscopy and Studies Nuclear Magnetic Resonance (NMR) of Cu&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;Zn(Sn, Si)S&amp;lt;sub&amp;gt;4 &amp;lt;/sub&amp;gt; Compounds for Photovoltaic Applications

In this study, Si-doped Cu2ZnSnS4 compounds (Cu2ZnSn1-xSixS4, 0 ≤ x ≤ 1) were prepared by solid state reaction method for use of materials for photovoltaic cells. The structural and spectroscopic properties of the as-prepared compounds were studied by X-ray diffraction (XRD), 119Sn, 29Si and 65Cu Magic Angle Spinning nuclear magnetic resonance (MAS NMR) and Raman spectroscopy. The Si-substitution in the Sn-site induces three different types of XRD patterns which depend largely on the Si content in the compound. For 0 ≤ x ≤ 0.5, XRD analysis reveals the presence of a pure tetragonal phase of solid solution with I-42m as a space group. Mixed tetragonal and orthorhombic phases were observed for 0.5 1 at high content of Si (x ≥ 0.8). 119Sn MAS NMR spectra show the presence of Sn/Si disorder as a function of the Si content. The 65Cu MAS NMR spectra of the quadratic solid solution confirm the presence of the two copper sites (Cu-2a and Cu-2c) at 780 ppm while in the case of the orthorhombic solid solution samples, a very broad band is observed. The optical properties were investigated of all compounds by UV-Vis diffuse reflectance and the obtained optical band gap values (1.31 to 2.43 eV) confirm a semiconductor character.

Spectroscopic evaluation of UVI-cement mineral interactions: ettringite and hydrotalcite.

Portland cement based grouts used for radioactive waste immobilization contain high replacement levels of supplementary cementitious materials, including blast-furnace slag and fly ash. The minerals formed upon hydration of these cements may have capacity for binding actinide elements present in radioactive waste. In this work, the minerals ettringite (Ca6Al2(SO4)3(OH)12·26H2O) and hydrotalcite (Mg6Al2(OH)16CO3·4H2O) were selected to investigate the importance of minor cement hydrate phases in sequestering and immobilizing UVI from radioactive waste streams. U LIII-edge X-ray absorption spectroscopy (XAS) was used to probe the UVI coordination environment in contact with these minerals. For the first time, solid-state 27Al magic angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopy was applied to probe the Al coordination environment in these UVI-contacted minerals and make inferences on the UVI coordination, in conjunction with the X-ray spectroscopy analyses. The U LIII-edge XAS analysis of the UVI-contacted ettringite phases found them to be similar (>∼70%) to the uranyl oxyhydroxides present in a mixed becquerelite/metaschoepite mineral. Fitting of the EXAFS region, in combination with 27Al NMR analysis, indicated that a disordered Ca- or Al-bearing UVI secondary phase also formed. For the UVI-contacted hydrotalcite phases, the XAS and 27Al NMR data were interpreted as being similar to uranyl carbonate, that was likely Mg-containing.

Reactions of metal chlorides with hexamethyldisilazane: Novel precursors to aluminum nitride and beyond

AbstractMetal nitrides are intensely investigated because they can offer high melting points, excellent corrosion resistance, high hardness, electronic and magnetic properties superior to the corresponding metals/metal oxides. Thus, they are used in diverse applications including refractory materials, semiconductors, electronic devices, and energy storage/conversion systems. Here, we present a simple, novel, scalable and general route to metal nitride precursors by reactions of metal chlorides with hexamethyldisilazane [HMDS, (Me3Si)2NH] in tetrahydrofuran or acetonitrile at low temperatures (ambient to 60°C/N2). Such reactions have received scant attention in the literature.The work reported here focuses primarily on the Al‐HMDS precursor produced from the reaction of AlCl3 with HMDS (mole ratio = 1:3) characterized by matrix‐assisted laser desorption/ionization‐time of flight, Fourier‐transform infrared spectroscopy, thermogravimetric analysis‐differential thermal analysis, and multinuclear nuclear magnetic resonance spectroscopy (NMRs) for chemical and structural analyses. The Al‐HMDS precursor heated to 1600°C/4 h/N2 produces aluminum nitride, characterized by X‐ray powder diffraction, X‐ray photoelectron spectroscopy, scanning electron microscopy/energy‐dispersive X‐ray spectroscopy, and magic‐angle spinning NMR. On heating to 800–1200°C/4 h/N2, the precursor transforms to an amorphous, oxygen‐sensitive powder with very high surface areas (&gt;200 m2/g) indicating nanosized particles, which can be used as additives to polymer matrices to modify their thermal stabilities. Al2O3 is also presented in the final product after heating, due to its high susceptibility to oxidation.This approach was extended via proof‐of‐concept studies to other metal chloride systems, including Zn‐HMDS, Cu‐HMDS, Fe‐HMDS, and Bi‐HMDS. The formed precursors are volatile, offering the potential utility as gas‐phase deposition precursors for their corresponding metal nitrides.

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.

Trash into treasure: Converting waste polyester into C3N4-based intramolecular donor-acceptor conjugated copolymer for efficient visible-light photocatalysis

Carbon nitride (C3N4) is regarded as one of the most prospective photocatalysts for environmental remediation. The design of intramolecular donor-acceptor (D-A) conjugated structure has aroused particular interest for improving visible-light photocatalytic activity of C3N4, but remains a huge challenge. Herein, a novel C3N4-based D-A conjugated copolymer is synthesized by incorporating aromatic ring into the C3N4 skeleton by copolymerization of melamine with terephthalic acid from the in-situ controlled degradation of recycled poly(ethylene terephthalate) catalyzed by ZnO at 360 °C. The results of X-ray diffraction, solid-state 13C cross-polarization magic-angle spinning nuclear magnetic resonance, thermodynamics analysis, and X-ray photoelectron spectroscopy confirm the structure of C3N4-based D-A conjugated system, consisting of terminal amino group of the tri-s-triazine unit as electron-donating group and aromatic ring as acceptor. Notably, the C3N4-based D-A conjugated copolymer displays shorter lifetime of light-induced charge carriers, lower photoluminescence emission, and larger photocurrent response than pristine C3N4, certifying that the D-A conjugated system significantly promotes the separation efficiency of light-induced charge carriers. As such, the C3N4-based D-A conjugated copolymer displays high performance in the photocatalytic degradation of Amido black 10B upon visible light illumination, of which the kinetic constant is 101 times that of unmodified C3N4. Lastly, reactive oxygen species including ·OH, ·O2- and 1O2 are proved to be the main active sites. This work not only offers new insights into the synthesis of efficient C3N4-based D-A conjugated copolymers, but also will inspire new paradigms toward sustainable transformation of waste plastics into value-added products for environmental remediation.

Crystal Structure and Energetics of Arsenic(III)-Oxide Intercalates with Rubidium Chloride and Their Comparison with Isostructural Intercalates of Potassium Halides

Two intercalation compounds of arsenic(III) oxide and rubidium chloride have been crystallized and characterized. The first, anhydrous RbCl·2As2O3 (PRbCl), crystallizes in space group P6/mmm with cell parameters a = 5.23520(16) Å and c = 9.0495(4) Å, and it is isostructural with anhydrous intercalates of arsenic(III) oxide with potassium halides. The second one, RbCl·As2O3·1/2H2O (Y′RbCl), crystallizes in space group P6/mmm with a = 5.25072(17) Å and c = 12.6472(5) Å, and its crystal structure is very similar to that of KCl·As2O3·1/2H2O. In the case of a large single crystal of compound Y′RbCl, weak satellite reflections were observed. The commensurate superstructure that gives rise to them has been described using the supercell approach (a = 9.019(4) Å, c = 12.6433(7) Å) and briefly discussed. The structures of intercalates PRbCl and Y′RbCl have been studied by 87Rb solid-state magic-angle spinning nuclear magnetic resonance (ssNMR) spectroscopy which has indicated the presence of one and two rubidium cations with distinct chemical environments, respectively. The comparison of these spectra allowed for the assignment of peaks to rubidium cations occupying particular sites. Infrared (IR) spectra and 1H ssNMR spectra of intercalate Y′RbCl have revealed dynamic disorder of water molecules occurring on the time scale of the IR experiment. Last but not least, interlayer interaction energies as well as thermodynamic stability of intercalate PRbCl and isostructural arsenic(III)-oxide intercalates with potassium halides have been studied computationally in the framework of density functional theory. Results of the calculations indicate that an increase in the size of anions or cations leads to an increase in the stability of the obtained intercalates.