29Si Magic Angle Spinning NMR Research Articles

Structure of nanocrystalline calcium silicate hydrates: insights from X-ray diffraction, synchrotron X-ray absorption and nuclear magnetic resonance.

The structure of nanocrystalline calcium silicate hydrates (C-S-H) having Ca/Si ratios ranging between 0.57 ± 0.05 and 1.47 ± 0.04 was studied using an electron probe micro-analyser, powder X-ray diffraction, 29Si magic angle spinning NMR, and Fourier-transform infrared and synchrotron X-ray absorption spectroscopies. All samples can be described as nanocrystalline and defective tobermorite. At low Ca/Si ratio, the Si chains are defect free and the Si Q3 and Q2 environments account, respectively, for up to 40.2 ± 1.5% and 55.6 ± 3.0% of the total Si, with part of the Q3 Si being attributable to remnants of the synthesis reactant. As the Ca/Si ratio increases up to 0.87 ± 0.02, the Si Q3 environment decreases down to 0 and is preferentially replaced by the Q2 environment, which reaches 87.9 ± 2.0%. At higher ratios, Q2 decreases down to 32.0 ± 7.6% for Ca/Si = 1.38 ± 0.03 and is replaced by the Q1 environment, which peaks at 68.1 ± 3.8%. The combination of X-ray diffraction and NMR allowed capturing the depolymerization of Si chains as well as a two-step variation in the layer-to-layer distance. This latter first increases from ∼11.3 Å (for samples having a Ca/Si ratio <∼0.6) up to 12.25 Å at Ca/Si = 0.87 ± 0.02, probably as a result of a weaker layer-to-layer connectivity, and then decreases down to 11 Å when the Ca/Si ratio reaches 1.38 ± 0.03. The decrease in layer-to-layer distance results from the incorporation of interlayer Ca that may form a Ca(OH)2-like structure, nanocrystalline and intermixed with C-S-H layers, at high Ca/Si ratios.

Polysiloxane microspheres functionalized with imidazole groups as a palladium catalyst support

Polysiloxane microspheres containing a large number of silanol groups were obtained by an emulsion process of modified polyhydromethylsiloxane. N‐substituted imidazole groups were grafted on these microspheres by the silylation of their silanol groups with N‐[γ‐(dimethylchlorosilyl)propyl]imidazole hydrochloride. The progress of the reaction was monitored using 29Si and 13C magic angle spinning (MAS) NMR and its impact on microsphere morphology was studied using scanning electron microscopy (SEM). The usefulness of the imidazole‐functionalized microspheres as a support for a metal catalyst was demonstrated by their reaction with PdCl2(PhCN)2. In this way a new heterogenized catalyst, Pd(II) complex with imidazole ligands supported on polysiloxane microspheres, was generated. This catalyst, MPd, was characterized using 13C and 29Si MAS NMR, X‐ray photoelectron, Fourier transform infrared and far‐infrared spectroscopies, X‐ray diffraction, SEM–energy‐dispersive X‐ray spectroscopy and wide‐angle X‐ray scattering. The catalyst appears in two structures, as Pd(II) complex and Pd(0) nanoclusters. Its catalytic activity was tested using a model reaction, the hydrogenation of cinnamaldehyde, and compared with that of an analogous complex operating in a homogeneous system. MPd showed a high activity in the promotion of hydrogenation of cinnamaldehyde. The activity in the substrate conversion was stable at least in five cycles of this reaction. The main product was hydrocinnamaldehyde which could be obtained with a yield above 70%. A mechanism of the reaction is proposed. Copyright © 2016 John Wiley &amp; Sons, Ltd.

Transparent and Dense Ladder-Like Alkylene-Bridged Polymethylsiloxane Coating with Enhanced Water Vapor Barrier Property.

Organic-inorganic hybrid composites have been well-studied as water vapor barrier materials for their long diffusion length of water vapor in coatings which can be realized by improving the aspect ratio of inorganic components and regularity of nanostructure in coatings. In this paper, dense organic-inorganic hybrid coating based on ladder-like alkylene-bridged polymethylsiloxane (ABPMS) was successfully fabricated through the hydrosilylation reaction between polymethylhydrosiloxane and diene (1,5-hexadiene or 1,7-octadiene) in toluene under Pt/C catalysis. Its ladder-like structure was verified by 29Si magic angle spinning (MAS) NMR, 13C MAS NMR, and in-plane and out-of-plane glance-incident X-ray diffraction (GIXRD) techniques. Its corresponding coating showed excellent water vapor barrier ability for a typical water-soluble crystal, potassium dihydrogen phosphate (KDP). When treated in 50% relative humidity (RH) condition at 25 °C for 8 months, the ABPMS coating with 100 nm thickness displayed a very low transmittance loss of 1.6% compared with the high transmittance loss of 10% for uncoated KDP. Moreover, the ABPMS coating showed good ultraviolet radiation resistance, thermal stability, low mechanical property, and excellent compatibility with hydrophobic antireflective (AR) coatings.

Palladium Nanoparticles Supported in the Nanospaces of Imidazolium-Based Bifunctional PMOs: The Role of Plugs in Selectivity Changeover in Aerobic Oxidation of Alcohols

Novel heterogeneous catalyst systems comprised of palladium nanoparticles immobilized into the nanospaces of imidazolium-based bifunctional plugged and unplugged periodic mesoporous organosilicas (BFPMO) have been described for the selective aerobic oxidation of alcohols in water. BFPMOs were characterized by N2 adsorption–desorption analysis, transmission electron microscopy (TEM), powder X-ray diffraction (PXRD), thermal gravimetric analysis (TGA), 29Si and 13C cross-polarization magic angle spinning (CP MAS) NMR spectroscopy, diffuse reflectance infrared Fourier transform spectroscopy (DRIFT), elemental analysis, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The catalytic activity of all plugged and unplugged catalysts was investigated in the aerobic oxidation of benzylic alcohols by emphasizing the effect of different physiochemical properties as well as the plugs on the reaction selectivity. While unplugged catalysts exhibited much better activity for the selective o...

Distinctive Spectral and Microscopic Features for Characterizing the Three-Dimensional Local Aluminosilicate Structure of Perlites

Expanded perlite and raw perlites of various origins were examined using solid-state NMR and Fourier transform infrared (FTIR) spectroscopies, as well as scanning electron microscopy, in an attempt to correlate the characteristics of aluminosilicate framework with the material’s expansion properties. The 27Al magic angle spinning (MAS) NMR spectra indicated that aluminum atoms in perlite are mainly tetrahedrally coordinated in Q4 structures not participating in the expansion process; two different octahedral Al species were also identified in perlite. Owing to the tetrahedra−octahedra transformations, perlite may be classified among the metastable materials. The 29Si MAS NMR and 1H–29Si CPMAS NMR spectra showed that Q3 and Q4 units are mostly abundant, a fact that explains the low cation exchange capacity of perlites. Deconvoluted FTIR and 29Si MAS NMR spectra are consistent regarding the relative Qn intensities which, together with the network geometry, determine the expansibility of raw perlites. The calculated variations of the Si–O–Si angle are more significant than those of the Si–O bond length, remarkably affecting the structure of the aluminosilicate network. Thus, perlite samples of increasingly fragmentary framework exhibit the highest expansion ratios. SEM micrographs monitored the expansion process differentiating between the low- and high-expansibility perlites.

Thermal and mechanical stability of lanthanide-containing glass–ceramic sealants for solid oxide fuel cells

Thermal stability of lanthanide (Ln = La, Nd, Gd, Yb) containing glass and glass–ceramics (GCs) was characterized for their application as sealants for solid oxide fuel cells (SOFCs). X-ray diffraction (XRD) in conjunction with the Rietveld-RIR and solid-state NMR techniques was employed to quantify the crystalline and amorphous fractions in the glasses sintered/heat treated at 850 °C in air for 1–1000 h. The structure and crystalline phase evolution of Ln containing aluminosilicate glasses depend markedly on the Ln3+ cation field strength over both short and intermediate length scales. Along with diopside, Ln containing silicate apatites, with general formula Ln9.33+2x(Si1−xAlxO4)6O2 (Ln = La, Nd and Gd; with x varying between 0 and 0.33), were observed in the GCs after the heat treatment periods of 1 to 1000 h at 850 °C, leading to moderately higher electrical conductivity. The substantial amount of the remaining glassy phase in Gd2O3-containing GC after 1000 h at 850 °C is likely to confer self-healing properties to this composition, in accord with the oxygen leakage measurements on thermal cycling. 29Si, 27Al and 11B magic-angle spinning (MAS) NMR spectra confirmed the results of the XRD RIR analysis. The values of Weibull characteristic strength and of average flexural strengths for all the GCs are higher than those reported for G-18 commercial glass (51 MPa), with Weibull modulus varying in the range 11.6–34.4 towards good mechanical reliability. Thermal shock resistance of model electrochemical cells made of yttria-stabilized zirconia (YSZ) was evaluated employing quenching from 800 °C in air and water. All the GC seals bonded well to YSZ and Sanergy HT metallic interconnects without gap formation. Suitable thermal expansion coefficient (9.7–11.1 × 10−6 K−1), mechanical reliability, high electrical resistivity, strong adhesion to Sanergy HT interconnects and YSZ, and sufficient thermal shock resistance indicate good suitability of the lanthanide-containing sealants for SOFC applications.

Post-synthetic modification of crystal-like periodic mesoporous phenylene-silica with ferrocenyl groups

Amination of crystal-like 1,4-phenylene-bridged periodic mesoporous organosilica (Ph-PMO) was achieved with about 35% conversion of phenylene groups. Ferrocenylimine groups were subsequently anchored onto this material by condensation of acetylferrocene with amino groups. Elemental analysis indicated that about 15% of amino groups in PMO-NH2 were derivatized, resulting in an iron loading of 0.21 mmol g−1. Evidence for the presence of ferrocenylimine groups in the derivatized material (PMO-Fc) was obtained from 13C cross-polarization (CP) magic-angle spinning (MAS) NMR and FT-IR spectroscopies. PMO-Fc was further characterized by 29Si MAS NMR spectroscopy, powder X-ray diffraction (XRD), N2 adsorption–desorption, and thermogravimetric analysis (TGA). Powder XRD and N2 adsorption–desorption data for PMO-NH2 and PMO-Fc indicated that the mesoporous structure and molecular-scale periodicity in PMO-NH2 were largely retained upon treatment with acetylferrocene. The material PMO-Fc was examined as a catalyst for the oxidation of styrene at 55 °C using hydroperoxides as oxidants. The reaction products were benzaldehyde (major) and styrene oxide (minor), with the aldehyde being formed in yields of 25–27% at 24 h. Recycling experiments indicated that the material was susceptible to leaching of catalytically active species into the liquid phase due to the pronounced water sensitivity of the azomethine linkage.

NaRb7(Si4–xGex)2 – Soluble Zintl Phases Containing Heteroatomic Tetrahedral ­[Si4–xGex]4– Clusters

AbstractThe quaternary phases NaRb7(Si4–xGex)2 (x = 1–3) crystallize with an NaRb7Ge8‐type structure and contain tetrahedral four‐atom clusters that consist of Si and Ge atoms. The quaternary phases possess larger cell volumes with increasing Ge amount. The formation of heteroatomic [Si4–xGex]4– clusters is indicated by chemically different Si environments, which were analyzed by means of solid‐state 29Si MAS (magic‐angle spinning) NMR spectroscopy of a 29Si‐enriched NaRb7(Si4–xGex)2 sample with x = 0.5 as well as quantum chemical calculations of the NMR coupling parameters. NaRb7(Si4–xGex)2 represents another rare example of a phase with exclusively tetrahedral clusters that readily dissolves in liquid ammonia. The nature of the heteroatomic clusters was further investigated by dissolution of NaRb7(Si4–xGex)2 with x = 2 in liquid ammonia. In the presence of MesCu (Mes = mesityl) and 18‐crown‐6 as a sequestering agent, crystals with the composition [Rb(18‐crown‐6)]2Rb2[(MesCu)2(Si4–xGex)](NH3)11 were isolated with x = 2.2(1). [(MesCu)2(Si4–xGex)]4– represents another isomer of a MesCu‐stabilized tetrahedral anion and supports the observation that Zintl phases, which contain solely tetrahedranide subunits, represent a new class of soluble Zintl phases.

Revisiting structure of silica gels from water glass: an 1H and 29Si MAS and CP-MAS NMR study

The silica gels, derived from water glass solution with pH adjusted at 3.0 and 9.9, were revisited to investigate their constitution, although water glass has been studied for last tens of decades on gelation. Solid-state nuclear magnetic resonance spectroscopy was applied to the nuclei 1H and 29Si, by the use of magic angle spinning (MAS), 1H → 29Si CP-MAS (CP: cross-polarization), and modern techniques such as 2D HETCOR (two dimensional heteronuclear correlation), and variable-contact time CP techniques. Gelation time (tgel) showed U-letter shape dependence on pH. All gels consisted of Qn groups (n: 2, 3, and 4), where Qn stands for a silicate unite [(O1/2)nSi (–O−)4−n] (n: 0–4). The analysis of the 1H → 29Si CP kinetics and 1H-29Si HETCOR spectra elucidated the presence of four kinds of 1H nuclei, i.e., those giving a peak at 6.9 ppm in chemical shift δ: 1H–OSi hydrogen bonded to H2O molecules; one at 4.3 ppm: 1H of adsorbed water molecules, hydrogen-bonded to the silanol groups; one at 1.7 ppm: 1H–OSi confined in the gel lattice, including that forming aggregations like Si–OH/NaO–Si; and one at 4.2 ppm: 1H of water molecules on the outermost hydration layer.

Magnesium analogues of aluminosilicate inorganic polymers (geopolymers) from magnesium minerals

Attempts to synthesise magnesium-containing analogues of aluminosilicate geopolymers from the 1:1 and 2:1 layer magnesiosilicate minerals chrysotile and talc, as well as the magnesium mineral sepiolite are reported. The effect of pre-treating these starting minerals by grinding and/or dehydroxylation was also investigated by XRD, 29Si and natural-abundance 25Mg solid-state magic angle spinning (MAS) NMR spectroscopy. The products from sepiolite most closely resembled an aluminosilicate geopolymer, setting at 40 °C to an X-ray amorphous product containing a broad characteristic 29Si MAS NMR resonance at −90 ppm. The 25Mg MAS NMR spectrum of this product also showed evidence that some of the Mg was located in tetrahedral sites, as expected for a conventional geopolymer. A similar 25Mg MAS NMR result was obtained for chrysotile, but talc proved to be extremely resistant to geopolymer synthesis, requiring treatment at 120 °C for 3 days to set to a friable material retaining the XRD and NMR characteristics of the original talc or its crystalline dehydroxylation products. This lack of reactivity may be related to the 2:1 layer-lattice talc structure, or to the fact that a suitably reactive amorphous product is not formed upon dehydroxylation.

Silicon carbide polytype characterisation in coated fuel particles by Raman spectroscopy and 29Si magic angle spinning NMR

The silicon carbide layer of a batch of as-produced TRISO (tristructural isotropic) coated fuel particles with zirconia kernels was characterised by Raman spectroscopy and magic angle spinning nuclear magnetic resonance (MAS-NMR). The techniques were evaluated as a probe for the evolution of SiC local structure as a function of chemical vapour deposition processing. Nuclear magnetic resonance resolved 29Si resonances for multiple hexagonal or cubic silicon local environments, consistent with a mixture of 6H, 15R and 4H polytypes, within a majority (36%) 3C–SiC target structure. Polarised Raman spectroscopy by contrast, showed some evidence of hexagonal and cubic local environments but no evidence for clearly defined hexagonal or orthorhombic polytypes. It was clear from the Raman that there was significant scattering from q>0 regions of the Brillouin zone, consistent with a loss of translational symmetry associated with stacking faults. Simulation and TEM images suggested that the signals observed in Raman and NMR correspond closer to a random arrangement of SiC layers in which structures similar to the various polytypes occur over short distances. As NMR is a probe of local environment, the signals obtained were similar to those that would come from a mixture of crystallites, each of a well-defined polytype. The NMR data was analysed quantitatively by fitting the spectra of known polytypes and by using a simple model to represent the random arrangement of layers in a heavily faulted crystal.

Influence of methyl‐modified silyl groups on the properties of polymers and Si/B/N/C ceramics derived from N‐silylated borazine derivatives

Thermal silazane cleavage of dichloroboryldisilylamines (SiClmMe3−m)N(SiMe3)(BCl2) (1: m = 1; 2: m = 2) at 196 °C leads to the borazine derivates [(SiClmMe3−m)NB(ClnMe1−n)]3 (3: m = 1, n = 0.185; 4: m = 2, n = 0.111) characterized by NMR and IR spectroscopy and mass spectrometry. Single‐crystal X‐ray diffraction structure analyses reveal (BN)3 units with unusual twisted boat conformations in both compounds. Additionally, more detailed studies are done to clear up the function of the by‐products (SiClmMe3−m)N(SiClMe2)(BClMe) formed during the cyclization step leading to asymmetrically boron substituted borazine derivatives. The single‐source precursors 3 and 4 were cross‐linked with methylamine producing polymers 3P and 4P, which were transformed into black amorphous materials with ceramic yields of 20.8 % and 50.3 %, respectively. Ceramic 4C (Si1.00B0.98 N2.55 C1.37O0.05) was further investigated by 11B and 29Si magic angle spinning (MAS) NMR spectroscopy. A combined study of high‐temperature TG analyses and X‐ray powder diffraction analyses confirms the thermal stability of 4C up to 1670 °C. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Synthesis and Mechanical Properties of Organic–Inorganic Hybrid Materials from Lignin and Polysiloxanes

The preparation of silica-containing organic-inorganic hybrid materials composed of kraft lignin, alkoxysilanes, and organic linkers was investigated. 3-Glycidyloxypropyltrimethoxysilane, 3-(triethoxysilyl)propylisocyanate (IPTES), and bis(trimethoxysilyl)hexane were selected as the most promising linkers. The best materials obtained showed improved mechanical and thermal properties compared with lignin itself. The reaction of the hydroxyl groups with IPTES and the sol-gel reaction between the organic linker molecules were studied by attenuated total reflectance FTIR and solid-state ²⁹Si magic-angle spinning NMR spectroscopy. The homogeneous composition was demonstrated by electron microscopy and energy-dispersive X-ray spectroscopy mapping. The mechanical properties were investigated by microindentation and dynamic mechanical thermal analysis.

Formation of a crosslinked POSS network by an unusual hydrosilylation: Thermo-oxidative stabilization of the α-cristobalite phase in its amorphous regions

A semicrystalline inorganic–organic hybrid crosslinked network containing polyhedral oligomeric silsesquioxane (POSS) cores was constructed by the unusual hydrosilylation of the terminal vinyl groups of an internal acetylene-containing silane linker by a POSS monomer. Products from the thermal treatments of this network in either argon or air at 250, 550, and 1000 °C, respectively, were characterized by Fourier transform infrared, Solid-state 13C and 29Si magic angle spinning NMR, X-ray diffraction and XPS analyses. The highly symmetrically functionalized POSS silica clusters, in the fluorite silica phase, in the network were found to remain unchanged on thermal treatment possibly due to the shielding of the silica core by the functionalities and a cancellation of thermal stresses on the silica core. Stabilization of the metastable α-cristobalite phase, which is typically formed on cooling by a β- to α-transition of the β-cristobalite phase formed above 1400 °C, was observed in the amorphous regions in the network sample treated only to 1000 °C in air. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Natural hydrous amorphous silica: Quantitation of network speciation and hydroxyl content by 29Si MAS NMR and vibrational spectroscopy

Natural and synthetic hydrous amorphous silicas were investigated with single-pulse 29Si magic angle spinning (MAS) NMR and with vibrational spectroscopic methods. Samples included a volcanically derived silica coating on young basalt from Kilauea, Hawaii, as well as hyalite (opal-AN), silica sinters, and synthetic silica gels and silicic acid. Pulse delays of up to an hour were employed for silica samples with slow spin lattice relaxation rates, and nearly fully relaxed spectra (90-100%) were demonstrably achieved for all samples. 29Si NMR spectra consisted of two broad, overlapping peaks at -111 and -102 ppm and a smaller peak at -92 ppm, corresponding to Q4, Q3, and Q2 sites, respectively. The Hawaiian silica coating and silicic acid samples displayed high Q3 and Q2 contents; in particular, the structural Si-OH content of the coating was unusually high for a natural silica (5.4 ± 0.4 wt% H2O). Saturation-recovery spectra of the Hawaiian silica with increasing delay times were consistent with “stretched exponential” relaxation behavior and three-dimensional distribution of paramagnetic centers. Attenuated total reflectance infrared (ATR-IR) and Raman spectra of the silica powders indicated fully amorphous structures, and displayed hydrous (SiO3OH) and anhydrous silicate vibrational bands in positions consistent with previous work. Raman spectra of some samples indicated modest grain to grain heterogeneity. Inferred Si-OH contents from ATR-IR band ratios were strongly correlated with hydroxyl contents calculated from NMR spectra. The high Si-OH content of the Hawaiian silica coating suggests it is diagenetically immature and has not been exposed to elevated temperatures.

Preparation and Photocatalytic Activity of Lanthanide Loaded Microporous Titanosilicate ETS-10 Catalysts

The three dimensional microporous titanosilicate, ETS-10, was synthesized by a hydrothermal synthesis route using TiCl 4 and a sodium silicate aqueous solution as starting materials. Lanthanide (La, Ce, Pr, Nd) loaded ETS-10 catalysts were prepared by the impregnation method. The catalysts were characterized by X-ray diffraction, 29 Si magic angle spinning NMR, UV-Vis diffuse reflectance spectroscopy, N 2 adsorption-desorption measurement, and X-Ray fluorescence spectroscopy. The degradation of methyl orange under near-UV light was used to investigate the photocatalytic activity of the catalysts in aqueous suspensions. The lanthanide loaded ETS-10 catalysts exhibit higher activity than the unmodified ETS-10. The combination of loading lanthanide and increasing the surface defects of ETS-10 by a HF treatment gave an enhancement of the photocatalytic activity, which became comparable with that of anatase TiO 2 . 以水玻璃和四氯化钛为原料, 在不使用有机模板剂、氟离子和晶种的条件下, 用水热法合成了钛-硅沸石 ETS-10, 将 La、Ce、Pr 和 Nd 四种稀土元素负载到合成的 ETS-10 上. 通过 X 射线粉末衍射、N 2 吸附-脱附、 29 Si 魔角旋转核磁共振、紫外漫反射光谱、X 射线荧光光谱等表征手段对负载前后的 ETS-10 进行了表征. 以有机染料甲基橙为底物, 考察了负载各种稀土及氢氟酸腐蚀对 ETS-10 的光催化活性的影响. 结果表明, 四种稀土元素的引入均可有效提高 ETS-10 的光催化活性. 反应活性提高的程度与稀土元素负载量有关. 对 ETS-10 同时进行氢氟酸腐蚀和稀土元素的负载, 可以将 ETS-10 的光催化活性提高近一倍, 与锐钛矿相 TiO 2 相当, 但前者更易分离. Microporous titanosilicate, ETS-10, was prepared and further modified by loading lanthanide or a HF treatment. The resulting catalysts showed a high photocatalytic activity comparable with that of anatase TiO 2 .

Synthesis, characterization and catalytic activity of acid–base bifunctional materials through protection of amino groups

Acid–base bifunctional mesoporous material SO3H-SBA-15-NH2 was successfully synthesized under low acidic medium through protection of amino groups. X-ray diffraction (XRD), N2 adsorption–desorption, transmission electron micrographs (TEM), back titration, 13C magic-angle spinning (MAS) NMR and 29Si magic-angle spinning (MAS) NMR were employed to characterize the synthesized materials. The obtained bifunctional material was tested for aldol condensation reaction between acetone and 4-nitrobenzaldehyde. Compared with monofunctional catalysts of SO3H-SBA-15 and SBA-15-NH2, the bifunctional sample of SO3H-SBA-15-NH2 containing amine and sulfonic acid groups exhibited excellent acid–basic properties, which make it possess high activity for the aldol condensation.

Nonaqueous Fluoride/Chloride Anion-Promoted Delamination of Layered Zeolite Precursors: Synthesis and Characterization of UCB-2

The delamination of layered zeolite precursor PREFER is demonstrated under mild nonaqueous conditions using a mixture of cetyltrimethylammonium bromide, tetrabutylammonium fluoride, and tetrabutylammonium chloride in N,N-dimethylformamide (DMF) as solvent. The delamination proceeds through a swollen material intermediate which is characterized using powder X-ray diffraction (PXRD). Subsequent addition of concentrated HCl at room temperature leads to synthesis of UCB-2 via delamination of the swollen PREFER material and is characterized using PXRD, transmission electron microscopy (TEM), and argon gas physisorption, which shows lack of microporosity in UCB-2. 29Si magic angle spinning (MAS) NMR spectroscopy indicates lack of amorphization during delamination, as indicated by the entire absence of Q2 resonances, and 27Al MAS NMR spectroscopy shows exclusively tetrahedral aluminum in the framework following delamination. The delamination process requires both chloride and fluoride anions and is sensitive to solvent, working well in DMF. Experiments aimed at synthesizing UCB-2 using aqueous conditions previously used for UCB-1 synthesis leads to partial swelling and lack of delamination upon acidification. A similar lack of delamination is observed upon attempting synthesis of UCB-1 under conditions used for UCB-2 synthesis. The delamination of PREFER is reversible between delaminated and swollen states in the following manner. Treatment of as-made UCB-2 with the same reagents as used here for the swelling of PREFER causes the delaminated UCB-2 material to revert back to swollen PREFER. This causes the delaminated UCB-2 material to revert back to swollen PREFER. Altogether, these results highlight delamination as the reverse of zeolite synthesis and demonstrate the crucial role of noncovalent self-assembly involving the zeolitic framework and cations/anions/structure-directing agent and solvent during the delamination process.

Examining correlations between composition, structure and properties in zircon-containing raw glazes

The effects of additions of zircon (5–17wt%) to conventional single firing ceramic glazes is examined. The structural and morphological characteristics of the glazes were determined by Scanning Electron Microscopy, X-ray diffraction, infra-red spectroscopy, as well as 27Al and 29Si magic angle spinning (MAS) NMR. The presence of zircon microcrystals was revealed by X-ray diffraction (XRD) combined with scanning electron microscopy (SEM) and EDAX microanalysis. The chemical durability of the glasses is revealed to be acceptable for certain practical applications. The color characteristics of the glazes obtained were estimated in the HunterLab system (L*C*h*, emission spectra). The outcomes of the study established correlations between composition, structure and some of the physical properties.

Structural and dynamic characterization of Li12Si7 and Li12Ge7 using solid state NMR

Local environments and lithium ion dynamics in the binary lithium silicide Li12Si7, and the analogous germanium compound have been characterized by detailed 6Li, 7Li, and 29Si variable temperature static and magic-angle spinning (MAS) NMR experiments. In the MAS-NMR spectra, individual lithium sites are generally well-resolved at temperatures below 200K, whereas at higher temperatures partial site averaging is observed on the kHz timescale. The observed lithium chemical shift ranges of up to 60ppm indicate a significant amount of electronic charge stored on the lithium species, consistent with the expectation of the extended Zintl–Klemm–Bussmann concept used for the theoretical description of lithium silicides. Furthermore the strongly diamagnetic chemical shifts observed for the lithium ions situated directly above the five-membered Si5 rings suggest the possibility of aromatic ring currents in these structural elements. This assignment is confirmed further by 29Si{7Li} CPMAS-heteronuclear correlation experiments. The 29Si MAS-NMR spectra of Li12Si7, aided by 2-D J-resolved spectroscopy, are well suited for differentiating between the individual sites within the silicon framework, while further detailed connectivity information is available on the basis of 2-D INADEQUATE and radio frequency driven recoupling (RFDR) spectra. Variable temperature static 7Li NMR spectra reveal the onset of strong motional narrowing effects, illustrating high lithium ionic mobilities in both of these compounds.