State 29Si Nuclear Magnetic Resonance Research Articles

Tailoring the hydrophobicity of wrinkled silica nanoparticles and of the adsorption medium as a strategy for immobilizing lipase: An efficient catalyst for biofuel production

Hydrophobic wrinkled silica nanoparticles (WSNs) were obtained by surface functionalization with perfluorodecyltriethoxysilane (PDTES) by chemical vapour deposition (CVD). Surface functionalization was made to design a hydrophobic surface to immobilize lipase in its open active conformation by interfacial activation. Moreover, to modulate the closed/open form equilibrium, favouring the open conformation, n-hexane was added to the water/lipase solution, creating a micro-oily environment. Physicochemical characterization of supports was carried out by solid state 29Si nuclear Magnetic Resonance (NMR), the Brunauer–Emmett–Teller (BET) method, thermogravimetric (TG) analysis, contact angle (CA) measurement, scanning electron microscopy (SEM) and Fourier transform infrared (FT-IR) spectroscopy. Three different supports for physical immobilization of lipase were prepared, differing in the degree of hydrophobicity. The effect of the different hydrophobicity and of the addition of n-hexane on the adsorption of lipase was evaluated. The hyperactivation of the best biocatalyst was tested in the hydrolysis and transesterification of sunflower seed oil and compared to free lipase. The reaction yields were 87% and 75% respectively for hydrolysis, and 93% and 56% respectively for transesterification. The results suggest that both the hydrophobicity of the support and the addition of n-hexane favour the adsorption of lipase in the active conformation.

Effects of preparation parameters on the characteristics of SiO2- and CoxOy-modified-TiO2 colloids prepared by hydrolysis of titanium alkoxide

A series of SiO2-, and CoxOy-modified-TiO2 colloids prepared by hydrolysis of titanium alkoxide were synthesized. The effects of concentrations of water, acid, cobalt chloride, and tetraethoxysilane on the characteristics of colloids were investigated. The rheologic characteristics of the sols were characterized by liquid state 29Si nuclear magnetic resonance (NMR), Raman spectroscopy, and photon correlation spectroscopy. It was found that an increase in the acid concentration from 1 to 60 mM resulted in a decrease of the particle size from 17 to 9 nm, while the diffusion coefficient increased with twofold. The presence of water shortened the formation time of sol, and the specific concentration of hydrochloric acid stabilized the colloid system. The presence of Co(II) chloride enhanced the hydrolysis rate of tetraethoxysilane and the condensation rate of hydroxy derivatives. In contrast, Ti(IV) tetra-n-butoxide showed the opposite effect, slowing these processes and decreasing the degree of condensation of siloxane chains. The results of this study can be used to optimize the composition of stable homogeneous solutions to synthesize TiO2, TiO2–SiO2, TiO2–CoxOy, and TiO2–SiO2–CoxOy sols.

Fast synthesis of hierarchical nanosized pure Si-Beta zeolite via a steam-assisted conversion method

Abstract A hierarchical nanosized pure Si-Beta zeolite was firstly prepared via a micro-zone synchronous crystallization method by steam-assisted conversion taking inorganic silicon sources as raw material. Neither zeolite seeds nor fluoride mineralizing agent was required, only a bit of organic template agent (TEAOH/SiO2 = 0.05) was sufficient for constructing a self-sustaining plate-like nanosized aggregation with high surface area (631.09 m2/g) and pore volume (0.7 cm3/g) after 24 h period, much less than reported (TEAOH/SiO2≥0.54, 7–21 d). The pure Si-Beta zeolite also had a superior hydrophobicity than that of hydrothermal synthesis due to the advantage of micro-zone mass transfer. All the properties of resulting samples were investigated by comprehensive characterizations, including X-ray diffraction, scanning and transmission electron microscopy, nitrogen adsorption-desorption, water adsorption, Flourier transform infrared and solid state 29Si nuclear magnetic resonance. Importantly, a “micro-zone synchronous crystallization” mechanism was proposed to explain the formation of mesoporous structure and intrinsic micropores, so as to providing the theoretical guidance for one-step synthesis of hierarchical Beta and other zeolites.

Functional Nano-Coating Materials by Michael Addition and Ring-opening Polymerization: Reactivity, Molecular Architecture and Refractive index

Understanding the molecular interaction and morphology of organic-inorganic hybrid materials is an important and fundamental assignment to develop novel high-performance materials. In this work, we developed two types of hybrid coating materials by using different silane coupling agents via Michael addition reaction and ring-opening polymerization. The changes in molecular interaction and morphology of the hybrid coatings due to chemical composition and curing temperature were studied by electron microscopy, spectroscopy and solid state 29Si nuclear magnetic resonance analysis. Fundamental differences were observed in HYBRID I and HYBRID II coatings during the nucleation stage that was dependent on the curing temperature. Higher curing temperature of the hybrid coatings resulted in improved uniformity and greater crystallinity of dispersed phases, and better control of the morphology compared with coatings cured at lower temperatures. The higher curing temperature provided more consistent nucleation sites for the growth of larger nanostructures of desired characteristics (e.g., size and surface features). There is great flexibility in synthesizingg these hybrid materials where different structure and morphology can be achieved to produce materials whose applications can range from adhesives to protective coatings. Refractive index results revealed that HYBRID I (90 °C) coating showed higher refractive index than HYBRID II (90 °C) coating.

Void Formation/Elimination and Viscoelastic Response of Polyphenylsilsesquioxane Monolith.

Polyphenylsilsesquioxane (PhSiO3/2) particles as an organic-inorganic hybrid were prepared using sol-gel method, and monolithic samples were obtained via a warm-pressing. The reaction mechanism of particles’ polymerization and transformation to the monolith under the warm-press were investigated using solid state 29Si nuclear magnetic resonance (NMR) spectrometer, thermal gravimetric-differential thermal analyzer (TG-DTA), mass spectrometer (MS) and scanning electron microscope (SEM). Transparent and void-free monoliths are successfully obtained by warm-pressing above 180 °C. Both the terminal –OH groups on particles’ surface and warm-pressing are necessary for preparation of void-free PhSiO3/2 monolith. From the load-displacement measurement at various temperatures, a viscoelastic deformation is seen for PhSiO3/2 monolith with voids. On the other hand, an elastic deformation is seen for void-free PhSiO3/2 monolith, and the void-free monolith shows much higher breakdown voltage.

Preparation, characterization and its flame retardance performance of microencapsulated ammonium polyphosphate/ bridged polysesquisiloxane polyurethane composites

A core shell material consisting of ammonium polyphosphate as core and 4,4-oxydianiline-formaldehyde resin as shell was prepared through a situ microencapsulation technology. The monomer of the polyurethane (PU) was modified to form bridged polysesquisiloxane. The purpose of modification is to improve the thermal stability of polyurethane matrix through the formation of networks. The degree of the networks was evaluated by solid state 29Si-nuclear magnetic resonance. The structure and hydrophobic property of microencapsulated flame retardant were characterized using X-ray photoelectron spectroscopy and water solubility. The results indicated that the microencapsulation of APP with 4,4′-oxydianiline-formaldehyde resin (OF resin) resulted in improved hydrophobicity. The thermal properties of final flame retardant were systematically analyzed through thermogravimetric analysis. Limiting oxygen index and UL-94 test were used to classfied the flame retardant properties of varying the composition of APP and OFAPP in silanol-terminated polyurethane composites. Pure PU exhibited an LOI of 17 % and failed the UL-94 test. The LOI values of the 40 % OFAPP-added composites can reach 41 % and pass V-0 level. The results revealed that the microcapsulation of commercial flame retardant can improve the flame retardance of the composites.

Controllable synthesis of niobium doped mesoporous silica materials with various morphologies and its activity for oxidative catalysis

Nb doped HMS-X (Nb-HMS-X) was synthesized by sol–gel/emulsion method using non-ionic tri-block copolymer surfactant PEO140PPO39PEO140 (P123) as a structure directing agent. The effect of synthesis condition on the pore morphology and nature of pore ordering was investigated. Small-angle X-ray Scattering (SAXS) revealed highly ordered pore structure in Nb-HMS-X. It is demonstrated by Field Emission Scanning Electron Microscopy (FESEM) that the materials possessed various morphologies such as, regular spheres, disordered and tube-spheres depending on synthesis conditions. The solid state 29Si nuclear magnetic resonance measurements showed that chemical environment of silicon atoms get modified significantly with synthesis condition. Furthermore, the synthesized niobium doped hollow mesoporous silica (Nb-HMS-X) was effective to catalyze ethyl benzene oxidation reaction where activation of C–H bond took place.

Resistance to fire of intumescent silicone based coating: The role of organoclay

The fire performance of a curable-silicone based coatings containing expandable graphite (EG) and an organoclay is evaluated in hydrocarbon fire scenario (standard UL1709) using a lab-scale furnace test. It is shown that the use of organoclay allows achieving better performance. The influence of the clay as additional filler is investigated on the fire performance and on the mechanical properties of the char. It is shown that the clay increases significantly the mechanical properties of the char and hence, the fire performance of the silicone based coating. In a next part, the silicone/clay material was characterized by electron microscopy, wide-angle X-ray scattering and solid state 29Si nuclear magnetic resonance (NMR). It evidences the nanodispersion of the clay into the silicone matrix and two main interactions: (i) intercalation of some silicate layers and (ii) chemical reactions between the hydroxyl groups of the clay and the silicone matrix. Finally, X-ray fluorescence of the residue after fire testing shows the organoclay is present uniformly throughout the thickness of the char, due to the previous interaction, and hence increasing the cohesion of the char.

Surface modification of cotton nanocrystals with a silane agent

The research herewith aims at obtaining cellulose nanocrystals with a reduced hydrophilic surface character using a silane with isocyanate groups (isocyanatepropyltriethoxysilane), which are very reactive to hydroxyl groups and thus, are readily able to react with the low quantity of free hydroxyl groups present in the cellulose nanocrystal surfaces, therefore, promoting surface modification. Cellulose nanocrystals were obtained by hydrochloric acid hydrolysis of cotton fiber and were characterized by X-ray diffraction, Fourier transform infrared spectroscopy (FTIR) and solid state 29Si nuclear magnetic resonance (NMR) and their morphologies were investigated by scanning and transmission electron microscopy techniques. The nanocrystals presented a needle-like geometry with a 10 nm approximate diameter and a 166 nm average length. FTIR, 29Si NMR and silicon mapping images showed that nanocrystal surface chemical modification was successfully achieved. Also, the results confirm that the chemical modification occurred mainly at the nanocrystal surface, keeping the morphological integrity of the nanocrystals. The applied methodology for surface modification of the cellulose nanocrystals provided nanofillers with more appropriate surface characteristics that allow the dispersion in polymeric matrices and the adhesion at filler-matrix interface to be obtained. This may result in a better performance of these nanocrystals as reinforcing agents of hydrophobic polymer matrices.

Short range order at the amorphous TiO2–water interface probed by silicic acid adsorption and interfacial oligomerization: An ATR-IR and 29Si MAS-NMR study

Adsorption and oligomerization of H4SiO4 at the amorphous TiO2–aqueous interface were studied using in situ Attenuated Total Reflectance Infrared (ATR-IR) and ex situ solid state 29Si nuclear magnetic resonance (NMR). The ATR-IR spectra indicate that a monomeric silicate species is present at low silicate surface concentration (ΓSi). Above a threshold ΓSi linear silicate oligomers are formed and these oligomers dominate the surface at high ΓSi. Interestingly the ATR-IR spectra of H4SiO4 on the TiO2 surface are very similar to those previously observed on the poorly ordered iron oxide phase ferrihydrite. The 29Si NMR spectrum of silicate on the TiO2 surface shows the presence of Si in three states with chemical shifts corresponding to isolated monomers (Q0), the ends of linear oligomers (Q1) and the middle of linear oligomers (Q2). The ratio of the area of the Q1 and Q2 peaks was ≈2:1 which is consistent with the proposed formation of linear silicate trimers by insertion of a solution H4SiO4 between adjacent suitably orientated adsorbed silicate monomers. A structural interpretation indicates that the observed interfacial silicate oligomerization behavior is a general phenomenon whereby bidentate silicate monomers on oxide surfaces are disposed towards forming linear oligomers by condensation reactions involving their two terminal Si–OH groups. The high surface curvature of nanometer sized spheres inhibits the formation of interfacial silicates with a higher degree of polymerization.

Poly(vinyltriethoxysilane) modified MWCNT/polyimide nanocomposites—Preparation, morphological, mechanical, and electrical properties

AbstractMulti‐walled carbon nanotube (MWCNT) modified by vinyltriethoxysilane (VTES) via free radical reaction has been prepared (poly (vinyltriethoxysilane) modified MWCNTs, PVTES‐MWCNT). Precursor of polyimide, polyamic acid has been synthesized by reacting 4,4′‐oxydianiline with 3,3′,4,4′‐benzophenone tetracarboxylic dianhydride. PVTES‐MWCNT were then mixed with polyamic acid and heated to 300 °C to form CNT/polyimide composite. During the imidization processes, the silanes on CNT surface reacted with each other and may be connected together by covalent bond (SiOSi). The PVTES‐MWCNT was analyzed by Fourier transform infrared and X‐ray photoelectron spectroscopy. The PVTES‐MWCNT/polyimide composites were analyzed by CP/MAS solid state 29Si nuclear magnetic resonance (NMR) spectroscopy. Morphological properties of the PVTES‐MWCNT/polyimide composites were investigated by scanning electron microscope and transmission electron microscope. Electrical conductivity increased dramatically comparing to the unmodified MWCNT/polyimide composites. Mechanical properties of nanocomposite were enhanced significantly by PVTES‐MWCNT. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 803–816, 2008

Effect of synthesis conditions on the mesoscopical order of mesoporous silica SBA-15 functionalized by amino groups

Mesoporous amine-functionalized SBA-15 silica has been synthesized directly by the co-condensation of tetraethyl orthosilicate (TEOS) and aminopropyl-trimethoxysilane (APTMS) under acidic conditions with an APTMS/(APTMS + TEOS) molar ratio of 10%. The effect of synthesis conditions, including TEOS pre-hydrolysis, as well as the heating temperature and time, on the mesoscopical order and pore structure of the functionalized SBA-15 have been studied in detail by means of powder X-ray diffraction, nitrogen sorption, transmission electron microscopy, infrared spectra and solid state 29Si nuclear magnetic resonance. A functionalized SBA-15 silica with a highly ordered two-dimensional P6 mm hexagonal symmetry and a narrow pore size distribution centered at 6 nm can be obtained if TEOS is allowed to pre-hydrolyze for 2 h. For the sample with TEOS pre-hydrolysis time of 4 h, aging at 50°C or 150°C leads to a more ordered pore arrangement compared to 100°C and also a narrower pore size distribution with larger pore volume. Increasing aging time is in favor of the formation of mesoscopically ordered structure, but fails to obtain a superior pore structure.

Direct synthesis of thiol-ligands-functionalized SBA-15: Effect of 3-mercaptopropyltrimethoxysilane concentration on pore structure

Mesoporous thiol-functionalized SBA-15 silicas have been directly synthesized by co-condensation of tetraethyl orthosilicate and 3-mercaptopropyltrimethoxysilane with triblock copolymer poly(ethylene glycol)-B-poly(propylene glycol)-B-Poly(ethylene glycol) as structure-directing agent under hydrothermal condition. Mesoporous structure was obtained after the surfactant removal by Soxhlet ethanol extraction. These materials have been characterized by means of powder X-ray diffraction, nitrogen sorption, transmission electron microscopy, thermogravimetry analysis, elemental analysis and solid state 29Si nuclear magnetic resonance. The effect of 3-mercaptopropyltrimethoxysilane concentration in the initial mixture on the pore structure of functionalized SBA-15, including pore ordering, surface area, pore size and pore volume, is investigated in detail. In order to functionalize the SBA-15 silicas without a significant change of pore structure, the molar concentration of 3-mercaptopropyltrimethoxysilane should be limited to less than 20%.

Synthesis-Morphology-Mechanical Properties Relationships Of Polymer-Silica Nanocomposite Hybrid Materials

ABSTRACTTwo types of polymer-silica nanocomposites have been prepared by undergoing free radical polymerization of 2-hydroxyethyl methacrylate (HEMA) either in the presence of HEMA-functionalized SiO2 nanoparticles (Type 1) or during the simultaneous in situ growing of the silica phase through the acid-catalyzed sol-gel polymerization of tetraethoxysilane (TEOS) (Type 2). Relationships between synthesis, morphology and mechanical properties are discussed mainly on the basis of solid state 29Si nuclear magnetic resonance spectroscopy (NMR), transmission electron microscopy (TEM), small angle X-ray scattering (SAXS), and dynamic mechanical analysis (DMA).

Structural investigation of ormosils with potential as host photonic materials

Class II ormosils in the systems: methyl, propyl, vinyl and phenyl silicates have been structurally investigated for their suitability as photonic materials and this paper is a precis of many data. From visible and near-infrared spectroscopy these ormosils have: (i) intrinsic optical windows in the visible and at 1.06, 1.3 and 1.55 μ m and (ii) low residual water, despite being synthesised at only 60° C. The residual water can be expelled under vacuum. Solid state29 Si nuclear magnetic resonance spectroscopy shows that matrix condensation increases as the organic content of the matrix is increased; this is accompanied by a decrease in BET surface area.

Ormosil coatings of high hardness

Organically modified silicates (ormosils) of two systems were coated on polyethyleneterephthalate (PET) substrates. One was the tetraethoxysilane (TEOS)-vinyltriethoxysilane (VTES) system and the other was the TEOS-tetraisopropyltitanate (TIPT)-VTES system. The reactions among the alkoxides were examined by liquid state 29Si nuclear magnetic resonance (NMR) spectroscopy. The chemical bonds between TEOS and VTES, between TEOS and TIPT, and between VTES and TIPT are shown in the spectra and the reaction schemes are proposed. Vickers hardnesses of the ormosil coatings were obtained by using the models developed by Jonsson and Hogmark, and the theoretical models developed by the authors were valuable to predict the hardness values. The ormosil coatings obtained in the present study were much harder than the hardest transparent plastics, and thus are very useful for hard or protective coatings on organic polymers.

An XAFS study of the poly-carbosilane conversion to SixC1−x

Abstract The pyrolysis process from polycarbosilane (PCS) to SixC1−x has been followed up to 1473 K mainly by means of Si K X-ray absorption fine structure spectroscopy and solid state 29Si nuclear magnetic resonance. The structural conversion from the starting PCS to the resulting amorphous SixC1−x phase has been discussed from the obtained X-ray absorption near edge structure and 29Si magic-angle spinning nuclear magnetic resonance results. The silicon environment of the original and pyrolyzed PCS samples has been studied by extended X-ray absorption fine structure results.

Study of calcium silicate hydrates by solid state high resolution 29Si nuclear magnetic resonance

Synthetic calcium silicate hydrates were hydrothermally prepared at temperatures between 100 and 200°C. Preparations of tobermorite, xonotlite, hillebrandite, gyrolite, kilchoanite, calciochondrodite, α-dicalcium silicate hydrate and tricalcium silicate hydrate were characterized by X-ray diffraction, scanning electron microscopy and infra-red spectroscopy. The products were examined by high resolution solid state 29Si nuclear magnetic resonance (NMR) spectroscopy. Spectra for tobermorite, xonotlite, hillebrandite and tricalcium silicate hydrate have previously been reported, hut spectra for gyrolite, kilchoanite, calciochondrodite and α-dicalcium silicate hydrate are reported for the first time. NM R spectra reveal information about phase structure suggesting that some of the postulated crystal structures are incorrect. NMR spectroscopy shows promise as a means of identifying constituent phases of the silicate matrix in autoclaved cement pastes.