29Si Solid-state Nuclear Magnetic Resonance Research Articles

Developing Innovative Cement Composites Containing Vine Shoot Waste and Superplasticizers.

The expansion of the construction industry requires large quantities of construction materials; therefore, the utilization of alternative raw materials that reduce the environmental impact and enhance the quality of the construction materials has received increasing interest. The comparative performance of 1% Dynamon SR3 or Dynamon SR41 superplasticizers on the properties of cement paste with 1 wt.% vine shoot waste addition (VSW) was investigated after 28 days using Fourier-transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), and solid-state 27Al and 29Si nuclear magnetic resonance (NMR) spectroscopy. VSW does not delay the formation of calcium hydroxide and C-S-H and a slight decrease of the -OH band in samples containing superplasticizers, suggesting that free lime is converted to carbonates. The highest degree of crystallinity was remarked for the samples with superplasticizers. The structure of the cement paste with VSW and superplasticizers was corroborated with mechanical properties, showing increased strength in using VSW and superplasticizers. The results showed that adding 1% VSW and superplasticizers does not change the performance of the cement paste but reduces the water-cement ratio. The combination of VSW and superplasticizers led to cement composite with improved structural and mechanical properties suitable for construction.

Sulfonic Acid-Grafted Hybrid Porous Polymer Based on Double-Decker Silsesquioxane as Highly Efficient Acidic Heterogeneous Catalysts for the Alcoholysis of Styrene Oxide.

β-Alkoxyalcohols generated from epoxide ring-opening reactions are significant due to their enormous value as pharmaceutical intermediates and fine chemicals. Using a phenyl-substituted double-decker-type silsesquioxane as the precursor, a hybrid porous material (PCS-DDSQ) was synthesized through a Scholl coupling reaction with an AlCl3 catalyst. Then, novel excellent Brønsted acid-derived silsesquioxane solid catalysts (PCS-DDSQ-SO3H-x) were successfully obtained through an electrophilic aromatic substitution reaction of chlorosulfonic acid on phenyl rings of PCS-DDSQ, fully characterized by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, powder X-ray diffraction, temperature-programmed desorption, water contact angle, Brunauer-Emmett-Teller model, thermogravimetric analysis, and solid-state 13C and 29Si nuclear magnetic resonance techniques. The catalytic behavior of the PCS-DDSQ-SO3H-x with different SO3H loadings for the methanolysis of styrene oxide was compared and evaluated. The presence of SO3H groups endows them with excellent catalytic abilities, achieving the highest values from PCS-DDSQ-SO3H-1 (the acid site of its catalyst is 1.84 mmol/g) as 99% conversion and 100% selectivity for the methanolysis of styrene oxide in 30 min, which shows superior catalytic properties of low dosage and high efficiency. Furthermore, the PCS-DDSQ-SO3H-1 catalyst can maintain high activity and selectivity after three cycles. This study provides a feasible method for the preparation of Brønsted solid acid catalysts with different acid loadings by introducing the sulfonic group into PCS-DDSQ.

Coal fly ash to Y zeolite of great purity and crystallinity: A new and green activation method of combined in situ microwave and ultrasound

Highly crystalline and pure Y (FAU) zeolite were synthesized from coal fly ash (CFA) using a combined in situ microwave and ultrasonic irradiation-assisted method, improving the extraction efficiency of silicon and aluminum from coal fly ash with limited energy usage relative to conventional microwave or ultrasound methods. Significant improvement in the combined method was evident following activation in 4 mol/L sodium hydroxide solution for 1 h at 100°C whereby 39.80 wt% conversion of CFA was attained along with 70.26 mol.% conversion of Si and 68.03 mol.% conversion of Al. Solid-state 29Si and 27Al magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectra were used to investigate the framework chemical coordination environment, while the temperature-programmed desorption of NH3 (NH3-TPD) and pyridine-Fourier transform infrared (Pyridine-FTIR) spectra were employed to quantitatively detect the acidity and types of acid sites of the sample. The Si to Al ratio (SAR) of the as-obtained CFA-based Y zeolite was 4.65 with a specific surface area of 916.10 m2/g, leading towards excellent CO2 adsorption (107.14 cm3/g at 0 °C). Furthermore, the thermocatalytic performance of the CFA-Y sample was analyzed in the conversion of cumene, with high silica commercial ultra-stable Y (USY) zeolite as a reference.

Role of Al Distribution in CO2 Adsorption Capacity in RHO Zeolites

Tailoring the CO2 adsorption performance of high-aluminum-containing zeolites is typically considered from the perspective of controlling the type and location of extra-framework cations. In this work, using solid-state 29Si nuclear magnetic resonance (NMR), we show that local order, i.e., the aluminum distribution within the framework of Na,Cs-RHO type zeolites with different Al contents, plays a fundamental role in governing the CO2 adsorption capacity and structural flexibility. From this analysis, the cation type and location within the RHO structure as a consequence of the framework Al distribution are not the only parameters that deserve consideration. This is despite their paramount importance in optimizing the adsorption capacity of samples with a fixed Al content. In addition, we observe strong correlations between the 29Si NMR barycenter and ellipticity of the eight-ring pore apertures and the nearest neighbor and next-nearest neighbor framework atom distances. From this analysis, we rationalize that the zeolite framework flexibility can be viewed as a consequence of the distribution of Si species rather than being exclusively a consequence of the type of cation loading only.

Use of Vine Shoot Waste for Manufacturing Innovative Reinforced Cement Composites

Due to the current concern with the environmental impacts produced by the construction industry, many studies have been conducted to capitalize on the advantages of waste to develop sustainable materials. The study reports an innovative, non-conventional cement-based composite material containing 10 wt.% vine shoot waste, representing a step forward toward the use of this lignocellulosic waste. The investigations were carried out using scanning electron microscopy with energy dispersive X-ray analysis, Fourier-transform infrared spectroscopy, thermogravimetric analysis, X-ray diffraction and solid-state 27Al and 29Si nuclear magnetic resonance spectroscopy. The addition of vine shoot waste to the cement paste increases the amount of hydration products (calcium silicate hydrate (CSH), calcium hydroxide (CH), calcium carbonate (CaCO3) and ettringite), leading to a more compact and dense structure. The structural characterization techniques also confirmed the formation of a higher amount of hydration products in the case of vine shoot waste added to the cement paste.

Direct Identification of Zeolite Beta Polymorphs by Solid-State 29Si Nuclear Magnetic Resonance Spectroscopy.

Stacking disorder and polymorphism in zeolite and zeolite-like materials hinder their structural characterization. In this work, we propose an advanced approach based on applying "pure shift" solid-state 29Si nuclear magnetic resonance (NMR) spectroscopy for the structural investigation of zeolitic materials containing intergrown polymorphs. The approach developed in the case study of zeolite beta allows for the resolution of 21 29Si signals, attributing them to non-equivalent T sites in polymorphs A, B, and C, reconstruction of individual 29Si magic angle spinning NMR spectra for each polymorph, and determination of the polymorph composition with higher accuracy than X-ray diffraction. The results reveal that two widely used synthetic routes for zeolite beta, alkaline and fluoride synthesis, lead to different polymorph compositions. These findings indicate that "pure shift" solid-state 29Si NMR can serve as a superior tool for the elucidation of polymorphism in zeolites.

29Si Solid-State NMR Analysis of Opal-AG, Opal-AN and Opal-CT: Single Pulse Spectroscopy and Spin-Lattice T1 Relaxometry

Single pulse, solid-state 29Si nuclear magnetic resonance (NMR) spectroscopy offers an additional method of characterisation of opal-A and opal-CT through spin-lattice (T1) relaxometry. Opal T1 relaxation is characterised by stretched exponential (Weibull) function represented by scale (speed of relaxation) and shape (form of the curve) parameters. Relaxation is at least an order of magnitude faster than for silica glass and quartz, with Q3 (silanol) usually faster than Q4 (fully substituted silicates). 95% relaxation (Q4) is achieved for some Australian seam opals after 50 s though other samples of opal-AG may take 4000 s, while some figures for opal-AN are over 10,000 s. Enhancement is probably mostly due to the presence of water/silanol though the presence of paramagnetic metal ions and molecular motion may also contribute. Shape factors for opal-AG (0.5) and opal-AN (0.7) are significantly different, consistent with varying water and silanol environments, possibly reflecting differences in formation conditions. Opal-CT samples show a trend of shape factors from 0.45 to 0.75 correlated to relaxation rate. Peak position, scale and shape parameter, and Q3 to Q4 ratios offer further differentiating feature to separate opal-AG and opal-AN from other forms of opaline silica. T1 relaxation measurement may have a role for provenance verification. In addition, definitively determined Q3/Q4 ratios are in the range 0.1 to 0.4 for opal-AG but considerably lower for opal-AN and opal-CT.

Experimental and Theoretical Solid-State 29Si NMR Studies on Defect Structures in La9.33+x(SiO4)6O2+1.5x Apatite Oxide Ion Conductors.

Oxide ion conductors can be used as electrolytes in solid oxide fuel cells, a promising energy-conversion technology. Local structures around the defects in oxide ion conductors are key for understanding the defect stabilization and migration mechanisms. As the defect contents are generally low, it is rather difficult to characterize the defect structure and therefore elucidate how oxide ions migrate. Solid-state nuclear magnetic resonance (NMR) spectroscopy is a powerful technique for probing the local structures. However, the interpretation of NMR signals mainly based on the empirical knowledge could lead to unprecise local structures. There is still controversy regarding the defect structures in the apatite-type interstitial oxide ion conductors containing isolated tetrahedral units. Here, we combine the experimental solid-state 29Si NMR spectroscopy with theoretical density functional theory calculations to investigate the defect structures in La9.33+x(SiO4)6O2+1.5x apatites. The results indicate that the 29Si resonance signals on the high field side of the main peak corresponding to the Si atoms in the bulk structure are related to La vacancies and there is no steady-state SiO5 in the defect structures. This finding provides new atomic-level understanding to the stabilization and migration of interstitial oxide ions in silicate apatites, which could guide the design and discovery of new solid oxide fuel cell electrolyte materials.

Preparation of microporous glass fiber cloth without cracking

A glass fiber cloth (GFC) with microporosity was prepared upon the suppression of crack generations. After the prepared GFC was heat-treated, it was slowly cooled to room temperature and then subsequently treated with hydrochloric acid. The experimental data through complementary techniques including scanning electron microscopy, nitrogen adsorption/desorption isotherm, solid-state 29Si nuclear magnetic resonance spectroscopy, and elemental analysis revealed the conversion of the slowly-cooled GFC into a microporous solid with no cracks in each glass fiber upon the alkaline leaching by hydrochloric acid. These results clearly indicated the formation of microporous GFC without cracking.

Internal carbonation of belite-rich Portland cement: An in-depth observation at the interaction of the belite phase with sodium bicarbonate

The potential for the internal carbonation of belite-rich Portland cement with the addition of sodium bicarbonate is proposed in the present study with a particular observation of the microstructural evolution of the belite phase. Cement paste samples having additional dosages of NaHCO3 of 0, 1, 2, and 5 wt% were fabricated and characterized by means of X-ray diffractometry, pH measurements, thermogravimetry analyses, isothermal calorimetry, and solid-state 29Si nuclear magnetic resonance spectroscopy. The test results indicated that the CO2 released from the added NaHCO3 was uniformly dissolved in the matrix, facilitating internal carbonation. In addition, the formation of C–S–H was further promoted upon the incorporation of NaHCO3, signifying a reaction of belite with the NaHCO3. Isothermal calorimetry results confirmed that the NaHCO3 enhanced the early reaction kinetics. Meanwhile, the pH value of the samples increased due to the anion exchange between the NaHCO3 and Ca(OH)2.

Synthesis of short-range ordered aluminosilicates at ambient conditions

We report here on structure-related aggregation effects of short-range ordered aluminosilicates (SROAS) that have to be considered in the development of synthesis protocols and may be relevant for the properties of SROAS in the environment. We synthesized SROAS of variable composition by neutralizing aqueous aluminium chloride with sodium orthosilicate at ambient temperature and pressure. We determined elemental composition, visualized morphology by microscopic techniques, and resolved mineral structure by solid-state 29Si and 27Al nuclear magnetic resonance and Fourier-transform infrared spectroscopy. Nitrogen sorption revealed substantial surface loss of Al-rich SROAS that resembled proto-imogolite formed in soils and sediments due to aggregation upon freezing. The effect was less pronounced in Si-rich SROAS, indicating a structure-dependent effect on spatial arrangement of mass at the submicron scale. Cryomilling efficiently fractured aggregates but did not change the magnitude of specific surface area. Since accessibility of surface functional groups is a prerequisite for sequestration of substances, elucidating physical and chemical processes of aggregation as a function of composition and crystallinity may improve our understanding of the reactivity of SROAS in the environment.

Titanium-modified MCM-41 molecular sieves as efficient supports to increase the hydrogenation abilities of NiMoS and CoMoS catalysts

Ti modified MCM-41-supported NiMo and CoMo catalysts and their respective Ti free reference catalysts were prepared, characterized, and tested for the hydrodesulfurization reactions. The samples were synthesized by well-known procedures, such as liquid crystal templating and successive impregnation method for the supports and catalysts, respectively. Ti precursor was directly incorporated into the micellar solution before adding the silica precursor at different molar Si/Ti ratios (x=75 and 50). Fourier transform infrared spectroscopy, solid-state 29Si-nuclear magnetic resonance, small- and wide-angle X-ray diffraction, and nitrogen physisorption were used as characterization techniques. Four sulfided catalysts were also characterized by high-resolution transmission electron microscopy. The catalysts showed important increases in the reaction rates during both thiophene and dibenzothiophene hydrodesulfurization when the support was structurally modified with Ti-atoms. The samples supported on Ti-MCM-41(75) presented a higher activity than those supported on Ti-MCM-41(50), and they were superior to their respective Si-MCM-41-supported NiMoS and CoMoS catalysts, even NiMoTiM75 and CoMoTiM75 catalysts presented better performance compared to the conventional NiMo/Al2O3 and CoMo/Al2O3 catalysts in the DBT hydrodesulfurization. Ti incorporation also enhanced the selectivities to the hydrogenated products, which could be beneficial to destabilize refractory S-containing molecules.

A novel approach to characterization of a relatively unstable intercalation compound under ambient conditions: revisiting a kaolinite-acetone intercalation compound.

Characteristics of a kaolinite-acetone intercalation compound prepared using a kaolinite N-methylformamide intercalation compound (Kaol-NMF) as an intermediate were obtained by a set of techniques with attention to suppressing evaporation and deintercalation of acetone. X-ray diffraction (XRD) with spectroscopic analyses, Fourier-transform infrared spectroscopy (FTIR) accompanied by solid-state 13C and 29Si nuclear magnetic resonance (NMR) spectroscopy with cross polarization (CP) and magic angle spinning (MAS) enable us to demonstrate full replacement of a pre-intercalated NMF monolayer with an acetone monolayer between the layers of kaolinite with an increase in the basal spacing from 1.08 nm (Kaol-NMF) to 1.12 nm. In addition, the appearance of an additional OH stretching band at 3630 cm-1 and the shift of the C[double bond, length as m-dash]O stretching band to a lower wavenumber, from 1714 to 1701 cm-1, in the FTIR spectrum, along with a downfield shift of the signal due to C[double bond, length as m-dash]O groups from 209 ppm, where a singlet was observed in the liquid-state 13C NMR spectrum of acetone in CDCl3, to 219 ppm in the 13C CP/MAS NMR spectrum, indicate hydrogen bond formation between interlayer hydroxyl groups of kaolinite and C[double bond, length as m-dash]O groups of the intercalated acetone molecules. These careful characterization studies provide information on an interaction between kaolinite and acetone under ambient conditions.

Quantitative Correlation between the Degree of Reaction and Compressive Strength of Metakaolin-Based Geopolymers.

For geopolymers (usually composed of unreacted precursor and gel), the compressive strength is controlled by two factors. The first is the degree of reaction, or, equivalently, the amount of gel formed, including any calcium silicate hydrate gel in calcium-containing mixtures. The second factor is the gel composition, generally given by the Si/Al ratio. These two parameters are interrelated for typical silicate-activated metakaolin geopolymers. By separating out effects of Si/Al ratio and degree of reaction, this study quantitatively correlates the degree of reaction with the compressive strength of metakaolin-based geopolymers with and without calcium. Solid-state 29Si nuclear magnetic resonance (NMR) aided with chemical extractions was used to determine gel amounts and composition for several geopolymer mixtures. The compressive strength was also measured for each mixture at 7 days. Both the increase of Na/Al ratio in mixtures without calcium and addition of external calcium increased the degree of reaction, and compressive strength correlated linearly (R2 > 0.88) with the degree of reaction.

Structure and ionic conductivity of Na3+xSc2SixP3-xO12 (x=0.0, 0.2, 0.4, 0.8) NASICON materials: A combined neutron diffraction, MAS NMR and impedance study

A knowledge of structural parameters that play a role in influencing ionic conduction is the key to the design of improved NASICON materials which have attracted significant attention in recent years as potential solid electrolytes for sodium ion batteries. In this article, we report the results of our study on a series of scandium-based NASICON compounds, namely Na3+xSc2SixP3-xO12 (x= 0.0, 0.2, 0.4, 0.8) that have been prepared by the ceramic route. These materials have been characterized by powder X-ray and neutron diffraction, as well as solid-state 23Na, 45Sc, 31P, and 29Si nuclear magnetic resonance (NMR) spectroscopy at room temperature (RT). The electrical conductivity of the compounds in the temperature range of RT ̶400 °C has been determined by impedance spectroscopy. Rietveld refinement of the diffraction patterns confirms monoclinic C2/c unit cell for the Na3Sc2P3O12 but indicates a rhombohedral R3‾c unit cell for Na3+xSc2SixP3-xO12 compounds. The local environments surrounding sodium, scandium, phosphorus and silicon atoms have been deduced from solid-state NMR. 23Na NMR results gave evidence of Na-ion mobility at RT. AC impedance measurements show that the total conductivity of the sample increases with increasing substitution of P with Si. However, it is much reduced for x = 0.8 composition. Na-ion conductivity of 2.4×10-3 S cm−1 at 30 °C has been measured in Na3.4Sc2Si0·4P2·6O12 compound, which is comparable to the best-performing polycrystalline NASICONs. Parameters such as the area of the bottleneck region, Na–Na hopping distances, and the activation energy for Na-ion conduction have been determined from the structural data. A correlation has been found between the conductivity and the ratio of Na site vacancy to Na site occupancy. Possible reasons for the significant variation of the Na-ion conductivity with x are also discussed in the context of the structure and Na site occupancy.

Effects of silane on reaction process and microstructure of metakaolin-based geopolymer composites

A series of metakaolin-based geopolymer (MG) organic-inorganic composites were prepared by incorporating with different contents of silane. The silane was used as coupling agent to recombine different components in geopolymer pastes. During the hydration process, the hydration heat evolution, structure and chemical compositions were obtained to characterize the reaction kinetics. The use of silane (APTES) retarded the geopolymer hydration significantly with the increase of silane content. Fourier transform infrared (FT-IR) spectroscopy and solid-state 29Si nuclear magnetic resonance (NMR) indicated that the tetrahedral structure ([SiO4]4- and [AlO4]4-) of aluminosilicate was decomposed and migrated and recombined to form a new tetrahedral network. SEM microscope images and EDS maps showed that the addition of silane enabled geopolymer to achieve a structural homogeneity, which resulted in the significant increase of the content of carbon and the formation of the chemical bonding reaction in organic-inorganic geopolymer composites.

Annealing induced structural evolution in feldspar dental glass-ceramics investigated by solid-state NMR spectroscopy

Glass-ceramics are an attractive oxide-based material routinely used for biomineral repair such as porcelain veneers in dental crown applications. The short- and long-range structure of a commercial glass-ceramic feldspar material, VITA VM9, has been investigated as a function of annealing temperature. The relative amounts of amorphous and crystalline components were monitored using a combination of powder X-ray diffraction and solid-state 23Na, 27Al, and 29Si nuclear magnetic resonance spectroscopy. The insight gained from this study was then applied to analyze a series of synthetic lab-grade ceramics Na0.5K0.5Al1–xMxSi3O8 (x ​= ​0.1; M ​= ​B, Al, Ga), whose onset of crystallization was found to resemble that of the commercial ceramic material.

Fundamental Insights into the Covalent Silane Functionalization of NiFe Layered Double Hydroxides.

Layered double hydroxides (LDHs) are a class of 2D anionic materials exhibiting wide chemical versatility and promising applications in different fields, ranging from catalysis to energy storage and conversion. However, the covalent chemistry of this kind of 2D materials is still barely explored. Herein, the covalent functionalization with silanes of a magnetic NiFe-LDH is reported. The synthetic route consists of a topochemical approach followed by anion exchange reaction with surfactant molecules prior to covalent functionalization with the (3-aminopropyl)triethoxysilane (APTES) molecules. The functionalized NiFe-APTES was fully characterized by X-ray diffraction, infrared spectroscopy, electron microscopy, thermogravimetric analysis coupled with mass spectrometry and 29 Si solid-state nuclear magnetic resonance, among others. The effect on the electronic properties of the functionalized LDH was investigated by a magnetic study in combination with Mössbauer spectroscopy. Moreover, the reversibility of the silane-functionalization at basic pH was demonstrated, and the quality of the resulting LDH was proven by studying the electrochemical performance in the oxygen evolution reaction in basic media. Furthermore, the anion exchange capability for the NiFe-APTES was tested employing CrVI , resulting in an increase of 200 % of the anion retention. This report allows for a new degree of tunability of LDHs, opening the door to the synthesis of new hybrid architectures and materials.

Facile Fabrication of Lilium Pollen-like Organosilica Particles.

Organosilica particles with a novel lilium pollen-like morphology were synthesized by a one-step sol-gel method. The hydrolysis and co-condensation of vinyltrimethoxysilane (VTMS) and tetraethoxysilane (TEOS) took place in an aqueous medium with ammonia as the catalyst. The growth process of the organosilica particles was tracked by scanning electron microscopy (SEM). The bulk and surface composition of the lilium pollen-like organosilica particles were characterized by solid-state 29Si nuclear magnetic resonance (NMR) spectroscopy and X-ray photoelectron spectroscopy (XPS), respectively. In addition, bowl-like, golf ball-like, and walnut kernel-like organosilica particles could also be obtained by changing the concentration of ammonia, the amount of silane precursors, or the reaction medium. This study provides a facile method to prepare nonspherical organosilica particles with controllable morphologies.

A new peak fitting method for 1D solid-state 29Si NMR spectra based on singular spectrum analysis

[Formula: see text]Si Nuclear Magnetic Resonance (NMR) can measure the molecular structure of silicate in oilfield reinjection water. However, noise in [Formula: see text]Si NMR spectra (NMRS) affects the determination of silicate molecular structure type. To solve this problem, a new peak fitting method (Two-step Greedy-Singular Spectrum Analysis-Gaussian Fitting Method, TSG-SSA-GFM) is proposed in this paper. This method first uses TSG to determine the embedding dimension, then uses SSA to determine the characteristic peak position. Finally, GFM is used to calculate the molar ratio of characteristic peaks. The results show that TSG can quickly determine the embedding dimension and reduce computation by at least 50% vs. the global ergodic method. The mean deviation of characteristic peak positions determined by SSA is 0.07 ppm, while Discrete Wavelet Transform (DWT) and Empirical Mode Decomposition (EMD) cannot determine characteristic peaks of [Formula: see text]Si NMRS containing overlapping peak. The average [Formula: see text]-squared of Gaussian fitting of [Formula: see text]Si NMRS is 98.4% while Lorentzian is 90.6%. Therefore, this study provides an important method for quantitative analysis of [Formula: see text]Si NMRS.