Silicon oxycarbide glasses derived from polymeric networks with different molecular architecture prepared by hydrosilylation reaction

We have prepared two polysiloxane networks with different molecular structures and similar compositions as suitable precursors of silicon oxycarbide glasses (SiOC), in order to understand the influence of the molecular architecture of the polymeric networks on the structure of these glasses. The structural evolution from the polymeric precursor to glasses was followed by solid-state ²⁹Si magic angle spinning nuclear magnetic resonance (²⁹Si MAS NMR) and FTIR spectroscopies, X-ray diffraction, thermogravimetric analysis, and density measurements up to 1000 °C. The high- temperature behavior of SiOC glasses, up to 1600 °C, was studied by X-ray diffraction, and ²⁹Si MAS NMR spectroscopy. The formation of carbosilane bridges in the polymeric networks during the hydrosilylation reaction contributed to the generation of a larger amount of carbidic sites in the final products. An increase in the pyrolysis temperature led to a distribution of silicon sites and crystallization profiles that depended on the molecular architecture of the polymeric precursors.     

Effect of B2O3 addition on microhardness and structural features of 40Na2O-10BaO-xB2O3-(50-x)P2O5 glass system

Phosphate glasses having composition, 40Na₂O-10BaO-xB₂O₃-(50-x)P₂O₅, wherex = 0–20 mol% were prepared using conventional melt quench technique. Density of these glasses was measured using Archimedes principle. Microhardness (MH) was measured by Vicker’s indentation technique. Structural studies were carried out using IR spectroscopy and³¹P and¹¹B MAS NMR. Density was found to vary between 2.62 and 2.77 g/cc. MH was found to increase with the increase in boron content.³¹P MAS NMR spectra showed the presence of middle Q² groups and end Q¹ and Q⁰ groups with P-O-B linkages. FTIR studies showed the presence of BO₃ and BO₄ structural units along with the depolymerization of phosphate chains in conformity with³¹P MAS NMR.¹¹B NMR spectra showed increase in BO₄ structural units with increasing boron content. The increase in MH with B₂O₃ content is due to the increase of P-O-B linkages and BO₄ structural units as observed from MAS NMR studies resulting in a more rigid borophosphate glass networks.     

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.     

Structural and spatially resolved studies on the hardening of a commercial resin-modified glass-ionomer cement

A commercial photopolymerizable resin-modified glass-ionomer (Fuji II LC) was studied using a variety of nuclear magnetic resonance (NMR) techniques. ¹H and ¹⁹F stray-field imaging (STRAFI) enabled to follow the acid–base reaction kinetics in self-cured (SC) samples. Gelation and maturation processes with 25 min and 40 h average time constants, respectively, were distinguished. In self- & photo-cured (SPC) samples, two processes were also observed, which occurred with 2 s and 47 s average time constants. ¹H, ²⁷Al and ²⁹Si magic angle spinning (MAS) NMR, ¹³C cross-polarization (CP)/MAS NMR and ²⁷Al multiple quanta (MQ)MAS NMR spectroscopy were used to obtain structural information on the glass and cements that were either SC or SPC. The presence of methacrylate groups was identified in the solid component. Unreacted hydroxyl ethylmethacrylate (HEMA) was detected in self-cured cement. ²⁷Al data showed that approximately 28% and 20% of Al is leached out from glass particles in SC and SPC samples, respectively. The upfield shift detected in ²⁹Si MAS NMR spectra of the cements is consistent with a decrease in the number of Al species in the second coordination sphere of the silicon structures. Scanning electron microscopy (SEM) showed existence of 3D shrinkage of the cement matrix in photo-cured cements.     

Synthesis of Novel Supramolecular Complexes from Fullerene C60 and Two New Cavitands

Abstract

Two new cavitands were prepared, their reactions with fullerene C₆₀ afford novel complexes, hosting one and two C₆₀ molecules. The cavitands were studied by solution NMR and solid‐state ¹³C, ²⁹Si CP‐MAS NMR. The complexes obtained were characterized by elemental analysis, ¹³C and ²⁹Si CP‐MAS NMR, UV and FTIR. In the complexes π–π, CH–π and n–π interactions were observed.     

Quantitative Aspects of 27Al MAS NMR of Calcium Aluminoferrites

²⁷Al MAS NMR spectra of synthetic calcium aluminoferrites, Ca₂Al_xFe_2−xO₅ with x = 0.93, 1, 1.33, reveal only a few percent of the expected intensity for the ²⁷Al central transition, indicating that the calcium aluminoferrite phase in Portland cements can barely be observed by ²⁷Al MAS NMR. This result supports the use of ²⁷Al MAS NMR for quantitative analysis of the tricalcium aluminate phase in Portland cements.     

Synthesis and characterization of a basic molecular sieve: Nitrogen-incorporated SAPO-34

Microporous nitrogen-incorporated SAPO-34 molecular sieves were synthesized by thermal post-treatment of SAPO-34 in flowing dry ammonia at elevated temperatures. The results of property characterized by DRIFTS of CO₂ adsorption and CO₂–TPD showed that basic sites existed on the surface of nitridized samples probably due to the presence of nitrogen-containing species incorporating into the framework of SAPO-34 molecular sieves. The changes in structure of nitrogen-incorporated samples were investigated by ²⁷Al MAS NMR, ³¹P MAS NMR spectra X-ray diffraction and BET surface area measurements. It was found that nitrogen-incorporated SAPO-34 still kept good crystallinity and high specific surface area of precursors. And N-containing species had incorporated into the framework of samples during nitridation, in which N atom presumably bounded to Al and P atoms formed N-containing groups, but unfortunately some of them were not ascribed.     

Characterization of wurtzite indium nitride synthesized from indium oxide by In-115 MAS NMR spectroscopy

Wurtzite indium nitride (w-InN) powders synthesized from the reaction of indium oxide (In₂O₃) with ammonia were characterized by ¹¹⁵In magic-angle spinning (MAS) NMR spectroscopy and nitrogen analyzer. The powders were not a single phase of w-InN but a mixture of w-InN and In-incorporated w-InN. The incorporation of In metal in InN lattice due to thermal decomposition caused the ¹¹⁵In MAS NMR peak of w-InN to be downfield shifted and might be responsible for the increase in the band gap of w-InN.     

Structural studies of geopolymers by <Superscript>29</Superscript>Si and <Superscript>27</Superscript>Al MAS-NMR

A systematic study of geopolymers by ²⁹Si and ²⁷Al MAS NMR has been carried out in an attempt to understand polymer structural details. ²⁷Al MAS NMR data shows that transient aluminium species are formed during the reaction of metakaolin with NaOH. Interaction of silicate anions with the aluminium sites of metakaolin was evident during the synthesis of geopolymers as observed from low field shift of ²⁹Si MAS NMR resonance lines of silicate centres. As the reaction progresses, the coordination of aluminium (IV, V and VI) in metakaolin changes almost completely to IV. ²⁹Si MAS NMR of selected compositions of the ternary system of sodium silicate, metakaolin and aqueous alkali reveals that geopolymerisation occurs in a distinct compositional region. At high alkalinity [> 30% (mol/mol) overall Na²O content], connectivity of silicate anions is reduced, consistent with poor polymerisation. At low alkalinity [<10% (mol/mol) overall Na²O content], a clear ²⁹Si NMR resonance line due to unconverted metakaolin is observed. NMR spectra were recorded from a series of samples with a fixed Na²O content (20 mol%) and varied SiO²/Al²O³ ratio to observe aluminium substitution in the cross-linked silicon tetrahedra of polymer network. Aluminium insertion into the silicate network is confirmed from the observed ²⁹Si NMR shift as a function of Si/Al ratio. The identification of the presence or absence of metakaolin in the cured geopolymer product is not possible even by ²⁹Si NMR as the signal from metakaolin is indistinguishable from a broad ²⁹Si NMR peak consisting of many resonance lines from the network of cross-linked silicon/aluminium tetrahedra. In an attempt to identify metakaolin signal, we prepared geopolymers with higher SiO²/Al²O³ molar ratios. Since aluminium substitutions in the silicate tetrahedral network are decreased, this results in better-resolved ²⁹Si NMR lines. The ²⁹Si NMR signal due to metakaolin is then distinguishable in the spectra of cured products in a series of samples with 3 to 11 mol% metakaolin. These results indicate that a geopolymer structure is a network of silicon/aluminium tetrahedra with some presence of unreacted metakaolin. The silicon/aluminium tetrahedra might have connectivity ranging from 1 to 4.     

Luminescence of heat-treated silicon-based polymers: promising materials for LED applications

A new strategy to obtain transparent, thermally stable, and formable photoluminescent materials for LED applications is presented. Starting from commercially available silicon-based polymers, luminescence properties are developed by means of simple heat treatment. Solid polymethylsilsesquioxane MK (Wacker-Besil^®PMS MK) and liquid poly(ureamethylvinyl)silazane Ceraset (Kion Ceraset^® PUVMS) were thermally treated between 200 and 700 °C for 2 h under Ar atmosphere. Photoluminescence properties were observed in all the samples. The structural rearrangements during thermal annealing were effective in order to red-shift the emission spectra of the untreated polymers to the visible range. The formation of dangling bonds and carbon sp², associated with the annealing procedure and confirmed by means of Electron Paramagnetic Resonance (EPR) spectroscopy and solid state Magic Angle Spinning NMR (MAS-NMR) contribute to the red-shift of the photoluminescence emissions of the polymers. After heat treatment at low temperatures (200, 300, and 400 °C), both the polymers show fluorescence in the UV range. While the polysiloxane reveals white luminescence after annealing at 500 and 600 °C, the polysilazane heat-treated at 500 °C exhibits emission in the blue-green range and is transparent. At higher temperatures the presence of free carbon counteracts the luminescence properties.     

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.     

29Si and 17O NMR investigation of the structure of some crystalline calcium silicate hydrates

This paper presents the results of a systematic investigation of the structure of ¹⁷O-enriched, hydrothermally synthesized 1.1-nm tobermorite, 1.4-nm tobermorite, jennite, calciochondrodite, xonotlite, and hillebrandite, using ²⁹Si magic angle spinning (MAS) NMR, ¹H-²⁹Si cross-polarization magic angle spinning (CPMAS) NMR, and ¹⁷O MAS NMR. The ¹⁷O and most of the ¹H-²⁹Si CPMAS results are the first reported for these phases. Six types of oxygen sites were observed in tobermorite and jennite, including both SiOH CaOH linkages. The structure of 1.4-nm tobermorite is similar to that of 1.1-nm tobermorite with about 26% of the Ca²⁺′s in the interlayers. The results support the proposed jennite structure in which silicate chains and rows of OH⁻ groups alternately occur along the CaO layers [1]. Jennite contains long, single silicate chains similar to those in 1.4-nm tobermorite, with SiOH sites primarily occurring on bridging tetrahedra, and there seems to be no interlayer Ca²⁺′s. Although the Si sites in xonotlite and calciochondrodite cross-polarize well, neither contains SiOH linkages.     

Novel polysiloxane microspheres: Preparation and application in chlorinated butyl rubber (CIIR) damping composites

Polysiloxane microspheres (PSM) were prepared from a linear siloxane polymer by a simple emulsion procedure. Then, novel modified polysiloxane microspheres (MPSM) containing Si-OH groups were generated by introducing of organic hindered phenol groups, which were exploited for the functionalization of the microspheres with hydroxyl groups. The structure and properties of PSM and MPSM were revealed by various analysis, such as FTIR, XRD, SEM, TG, BET, etc. These polysiloxane microspheres, PSM and MPSM, were then used as rubber reinforcing fillers. The PSM and MPSM offered obvious effects on the properties of chlorinated butyl rubber (CIIR) and can improve its damping performance in a different agree. In addition, thermal stability, thermal conductivity, tensile properties, and toughing and damping mechanisms of the rubber composites were also investigated.     

Preparation of aluminosilicate precursor by mechanochemical method from gibbsite-fumed silica mixtures

Aluminosilicate (mullite) precursor was prepared by mechanochemical treatment of gibbsite and fumed silica mixtures. The effect of grinding on its structure and thermal behaviour was examined by²⁷Al and²⁹Si MAS NMR, XRD, DTA-TG and FTIR. Thermal treatment of this precursor led to the crystallization of mullite at about 1200°C via a spinel-phase.²⁷Al and²⁹Si MAS NMR spectroscopies show lowering of mullitization temperature, which is associated with increased homogeneity of the precursor. Mechanochemical treatment of gibbsite and fumed silica mixtures resulted in the formation of a more homogeneous aluminosilicate precursor.     

Synthesis of acid-base bifunctional mesoporous materials by oxidation and thermolysis

A novel and efficient method has been developed for the synthesis of acid-base bifunctional catalyst SO₃H-MCM-41-NH₂. This method was achieved by co-condensation of tetraethylorthosilicate (TEOS), 3-mercaptopropyltrimethoxysilane (MPTMS) and (3-triethoxysilylpropyl) carbamicacid-1-methylcyclohexylester (3TAME) in the presence of cetyltrimethylammonium bromide (CTAB), followed by oxidation and then thermolysis to generate acidic site and basic site. X-ray diffraction (XRD) and transmission electron micrographs (TEM) show that the resultant materials keep mesoporous structure. Thermogravimetric analysis (TGA), X-ray photoelectron spectra (XPS), back titration, solid-state ¹³C CP/MAS NMR and solid-state ²⁹Si MAS NMR confirm that the organosiloxanes were condensed as a part of the silica framework. The bifunctional sample (SO₃H-MCM-41-NH₂) containing amine and sulfonic acids exhibits excellent acid-basic properties, which make it possess high activity in aldol condensation reaction between acetone and various aldehydes.     

(Na4BH4) guests inside aluminosilicate, gallosilicate and aluminogermanate sodalite host frameworks studied by H, B, and Na MAS NMR spectroscopy

We report tetrahydroborate aluminosilicate, gallosilicate and aluminogermanate sodalites studied by ¹¹B, ¹H and ²³Na MAS NMR spectroscopy. The spectral parameters are consistent with the local environments of each investigated nucleus obtained from the crystal structures. The ¹¹B MAS NMR spectra exhibit a sharp narrow line at about −49.0 ppm, which is assigned to BH₄⁻ enclathrated into the sodalite framework matrix. The lineshape of the signal shows no quadrupolar interactions due to discreteness and high symmetry of the BH₄⁻ unit as well as possible fast dynamic site exchange of hydrogen atoms. The ²³Na MAS NMR signals also show a narrow Gaussian lineshape, which clearly indicates a single type of sodium coordination, and a centrosymmetrical charge distribution around the sodium atom. The ¹H MAS NMR spectra can clearly distinguish between hydrogen in BH₄⁻ anions (−0.6 ppm), H₃O₂⁻ anions (1.2 ppm) and H₂O molecules (5.0 ppm). The structural properties of BH₄⁻ intercalation into sodalite framework matrix help connect the microporous materials to hydride-containing A, X and Y type zeolites.     

Syntheses of intercalation compounds of tetraamine in α-Zr(HPO4)2·H2O and the structures of guest molecules by solid state NMR

Conformational change of N,N′-Bis-(3-aminopropyl)-1,3-propanediamine (3P4A) intercalated in α-zirconium phosphate (α-ZrP) is reported. It is demonstrated that two kinds of intercalation compounds with different interlayer spacings, i.e., d=2.0 nm and d=1.7 nm, can be isolated by reacting at ca. 333 K and at ca. 298 K in aqueous suspension of 3P4A and α-ZrP, respectively. The lineshape analysis of ¹³C CP/MAS NMR spectra suggests that the conformation of 3P4A assumes the ‘straight’ form in the higher temperature product while it assumes the ‘bent’ form in the lower temperature product. According to this model, ³¹P MAS NMR spectra can be consistently assigned. It is found that ³¹P chemical shift values strongly depend on the bonding state of the amine groups in 3P4A molecule to the phosphate groups of α-ZrP. It is also shown that removing and/or controlling the amount of water molecules in the intercalation compounds are very important for the detailed assignment of the complicated ³¹P resonances.     

Investigation of Al-O-Al sites in an Na-aluminosilicate glass

This paper reports the presence of Al- O- Al linkages in an aluminosilicate glass where Si/Al = 1 by using 2D¹⁷O triple quantum MAS NMR technique (3Q MASNMR). The experiments were performed at external magnetic fields of 8.4 and 14.4T. Despite¹⁷OMAS NMR spectra of the sample in both fields do not give much information about the different kinds of linkages in the sample, 3Q MAS NMR spectrum shows clear evidence that there are some amounts of Al-O-Al linkages in the sample giving two completely resolved peaks. These two peaks were attributed to the Si-O-Al and Al-O-Al linkages on the basis of their chemical shifts and, quadrupolar coupling constants which are quite sensitive to the local structure.     

Preparation and characterization of α-chitin from cicada sloughs

In this study, a new source of insect chitin was proposed. Insect chitin was extracted from cicada sloughs by 1 M HCl and 1 M NaOH treatment for demineralization and deproteinization, respectively. The brown color of this chitin from cicada sloughs was removed using 6% sodium hypochlorite as an oxidizing agent. It was found that the insect chitin extracted from the cicada sloughs has a higher percent recovery than the chitin from rice-field crab shells. The chemical structure and physicochemical properties of α-chitin from cicada sloughs were characterized using elemental analysis (EA), attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), proton nuclear magnetic resonance spectroscopy (¹H NMR), solid-state ¹³C cross-polarization magic-angle-spinning nuclear magnetic resonance (CP/MAS) NMR spectroscopy, X-ray diffractometry (XRD), and thermogravimetry (TG). The degree of acetylation (DA) was determined by EA, ¹H NMR, and ¹³C CP/MAS NMR techniques. The DA values of chitin from cicada sloughs were in the range of 97% to 102% depending on each technique. Furthermore, it was found that the DA increased with an increasing thermal property and crystallinity.     

Synthesis and NMR characterization of SAPO-35 from non-aqueous systems using hexamethyleneimine template

SAPO-35 was synthesized using hexamethyleneimine template in non-aqueous systems. X-ray diffraction and scanning electron micrograph analysis shows the synthesized sample is pure and well crystalline. Presence of four stages (1.6%, 0.8%, 7.8% and 8.4%) of weight loss is observed by TG/DTA analysis. FT-IR analysis in the framework region shows the presence of tetrahedral T-O-T vibrations is similar to the other known aluminophosphate molecular sieves. FT-IR spectrum in the OH region shows stretching vibrations at 3631, 3604 and 3580 cm⁻¹ can be assigned to OH groups in bigger cages near S6R, in bigger cages near D6R and those actually confined inside the D6R, respectively. The spectra for the as-synthesized sample show a single symmetrical ²⁷Al MAS NMR line at δ = 36.26 indicating the presence of a single tetrahedral aluminium species. Where as ²⁹Si and ³¹P MAS NMR shows the presence of two peaks in both at (−89.9 and −95.15 ppm) and (−34.01 and −40.45 ppm) due to the Si substitution of P present in two different locations in double 6 ring (D6R) and in single 6 ring (S6R). ²⁷Al 3Q-MAS NMR shows two peaks for environmentally different tetrahedral aluminium atoms. This is the first time we are showing such a fact which is not observable using ordinary MAS NMR.