27Al Magic Angle Spinning Research Articles

Ni phosphide catalysts on Al2O3‐zeolite prepared by phosphidation for methyl palmitate hydroconversion

AbstractBACKGROUNDOne‐stage hydroconversion of fatty‐acid based feedstocks is a promising way to obtain high‐quality fuels. This process is based on hydrodeoxygenation, isomerization and hydrocracking reactions. In this work, Ni2P/Al2O3‐zeolite catalysts were synthesized and tested in hydroconversion of a model compound – methyl palmitate.RESULTSNi2P catalysts were prepared by in situ phosphidation of metallic Ni/Al2O3‐zeolite precursors by PPh3. Mixtures of zeolite (30 wt%) and boehmite were peptized and extruded to obtain the support granules. SAPO‐11, ZSM‐5, ZSM‐22, ZSM‐23 and ZSM‐12 were used as a zeolite component. The catalysts and supports were characterized by a range of physicochemical methods: chemical analysis (ICP‐AES), low‐temperature N2 adsorption, H2‐temperature programmed reduction, NH3‐temperature programmed desorption, Fourier transform infrared spectroscopy of adsorbed CO, X‐ray diffraction, transmission electron microscopy, X‐ray photoelectron spectroscopy, and 27Al and 31P magic angle spinning nuclear magnetic resonance. The catalysts were studied in methyl palmitate hydroconversion (one‐stage hydrodeoxygenation‐isomerization‐hydrocracking) in a continuous‐flow fixed bed reactor at 290–340 °C, 2 MPa, H2/feed = 600 Ncm3/cm3 and LHSV = 5.3 h−1. SAPO‐11 containing sample showed high selectivity to C15 and C16 iso‐alkanes (63%, at 340 °C), and all ZSM‐containing samples showed high selectivity to cracked C5–C9 products (55–100%, at 340 °C) with varying amounts of iso‐alkanes (31–57%, at 340 °C).CONCLUSIONThe results show that by choosing the zeolite component of the catalyst it is possible to finely tune product quality in the range from low‐temperature diesel fuel to jet fuel or gasoline. © 2024 Society of Chemical Industry (SCI).

Resolving intermediates during the growth of aluminum deuteroxide (Hydroxide) polymorphs in high chemical potential solutions

Aluminum hydroxide polymorphs are of widespread importance yet their kinetics of nucleation and growth remain beyond the reach of current models. Here we attempt to unveil the reaction processes underlying the polymorphs formation at high chemical potential. We examine their formation in-situ from supersaturated alkaline sodium aluminate solutions using deuteration and time-resolved neutron pair distribution function analyses, which indicate the formation of individual Al(OD)3 layers as an intermediate particle phase. These layers ultimately stack to form gibbsite- or bayerite-like layered heterostructures. Ex-situ characterization of the recovered precipitates using 27Al magic angle spinning nuclear magnetic resonance spectroscopy, Raman, X-ray diffraction, and scanning electron microscopy, suggests the presence of additional intermediate states, an amorphous compound bearing both tetrahededrally- and penta-coordinated Al3+. These observations reveal the complex pathways to form Al(OD)3 monolayers via either transient pentacoordinate species or amorphous-to-ordered transitions. The subsequent crystallization of admixed gibbsite/bayerite is followed by an Al(OD)3 monolayer attachment process.

Active species in chloroaluminate ionic liquids catalyzing low-temperature polyolefin deconstruction

Chloroaluminate ionic liquids selectively transform (waste) polyolefins into gasoline-range alkanes through tandem cracking-alkylation at temperatures below 100 °C. Further improvement of this process necessitates a deep understanding of the nature of the catalytically active species and the correlated performance in the catalyzing critical reactions for the tandem polyolefin deconstruction with isoalkanes at low temperatures. Here, we address this requirement by determining the nuclearity of the chloroaluminate ions and their interactions with reaction intermediates, combining in situ 27Al magic-angle spinning nuclear magnetic resonance spectroscopy, in situ Raman spectroscopy, Al K-edge X-ray absorption near edge structure spectroscopy, and catalytic activity measurement. Cracking and alkylation are facilitated by carbenium ions initiated by AlCl3-tert-butyl chloride (TBC) adducts, which are formed by the dissociation of Al2Cl7− in the presence of TBC. The carbenium ions activate the alkane polymer strands and advance the alkylation cycle through multiple hydride transfer reactions. In situ 1H NMR and operando infrared spectroscopy demonstrate that the cracking and alkylation processes occur synchronously; alkenes formed during cracking are rapidly incorporated into the carbenium ion-mediated alkylation cycle. The conclusions are further supported by ab initio molecular dynamics simulations coupled with an enhanced sampling method, and model experiments using n-hexadecane as a feed.

A Nanocrystalline ZSM‐5 for the Catalytic Cracking of Waste Cooking Oil

AbstractA series of hierarchical ZSM‐5 nanocrystalline aggregates (HNZ‐5) was synthesized using a hydrothermal method with tetrapropylammonium hydroxide as a structural guide. The HNZ‐5 samples having different Si/Al molar ratios all showed suitable hierarchical architectures and the maximum surface area was found to be 329 m2/g. The SEM image displayed the width of the individual crystal particles was ~100 nm, and its nanocrystalline clusters generated intercrystalline pores. Temperature‐programmed desorption with NH3 indicated that the total acidity of this material increased with increases in the Al3+ content to a maximum of 0.47 mmol/g at a Si/Al ratio of 15. In addition, 27Al magic angle spinning nuclear magnetic resonance spectra showed that the acid sites were associated with tetrahedral and octahedral Al sites. This HNZ‐5 was applied to the catalytic cracking of waste cooking oil model compound and gave a light olefin yield as high as 43.9 % at 550 °C. Extending the reaction time to 6000 min provided a yield of light olefins in excess of 30 %, which was higher than that achieved using traditional ZSM‐5. These data confirmed that the hierarchical pore structure of HNZ‐5 resulting from the self‐assembly of nanocrystals, together with exposed acidic sites, promoted the catalytic conversion of large molecules.

Low temperature phase transition mechanism of amorphous Al-oxalate to nano α-alumina

α-Alumina (α-Al2O3), widely used as a raw material or production in advanced manufacturing industry, has attracted much attention in terms of its preparation temperature. A simple dissolution-evaporation-precipitation process was employed to obtain the amorphous Al-oxalate (AAO) precursor, serving as the starting material for the low temperature preparation of nano α-Al2O3. The crystalline structure and thermal behavior of the AAO were compared with commercially available aluminum hydroxide (Al(OH)3) powder using the X-ray powder diffraction (XRD) instrument, the thermal gravity analysis and differential scanning calorimetry (TG-DSC). The phase transition mechanism of AAO was investigated by the fourier transform infrared spectroscopy (FTIR), transmission electron microscope (TEM), scanning electron microscope (SEM), and 27Al magic angle spinning nuclear magnetic resonance (27Al-MAS-NMR). The DSC results indicated that AAO underwent a phase transformation at 982 °C. The α-alumina diffraction peaks appeared in AAO at 1000 °C, while α-Al2O3 phase was observed for Al(OH)3 at 1200 °C. Furthermore, an absorption peak at 452 cm−1, corresponding to Al–O bond in α-alumina was detected at 1000 °C. The proposed low-temperature preparation mechanism of α-alumina from AAO is as follows: four coordination Al-oxalate species entities coexist within the AAO sample; with increasing temperature, organic acid functional groups oxidize and volatilize, resulting in the formation of tetra-coordinate [AlO4], penta-coordinate [AlO5], and hexa-coordinate [AlO6] atomic groups; these atomic clusters further polymerize to form a structurally dense α-alumina crystal at the nano-scale (∼50 nm) at around 1000 °C. The experimental findings present a novel approach and method for the low-temperature preparation of nano-sized alumina powder. Additionally, a feasible theoretical reference for the low-temperature phase transition mechanism of amorphous Al-oxalate was provided.

Monitoring the Geopolymerization Reaction of Geopolymer Foams Using 29Si and 27Al MAS NMR

This study aims to investigate the geopolymerization reaction of geopolymer foams produced with three different foaming agents: aluminum powder, zinc powder, and hydrogen peroxide. The geopolymerization reaction of geopolymer foam was monitored using the 27Al and 29Si magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy technique. 27Al MAS-NMR was used to monitor the reaction at an early stage, while 29Si and 27Al MAS-NMR analyses were employed at specific time intervals of 3, 6, 10, 15, and 28 days to examine the changes that occurred in the formed gel over time. We discussed in detail how the type of foaming agent used and the duration of the reaction both influence the quantity of gel formed and the amount of remnant fly ash. Our findings indicate that the type of foaming agent used affects the formation and structure of the gel, with aluminum powder leading to the highest gel formation. Additionally, the duration of the reaction plays a significant role in determining the quantity of remnant fly ash, with longer reaction times resulting in decreased fly ash content. This study sheds light on the relevance of understanding the role of foaming agents in the geopolymerization reactions of geopolymer foams and the influence of reaction time on the formed gel properties.

Influences of alumina type and sulfate content on hydration and physicochemical changes in Portland–limestone cement

This study explored the influence of alumina type and gypsum content on the hydration, mechanical properties, and chemical changes of Portland–limestone cement (PLC) using isothermal calorimetry, inductively coupled plasma-optical emission spectroscopy (ICP-OES), ionic chromatography (IC), compressive strength testing, X-ray diffraction (XRD), 27Al magic angle spinning nuclear magnetic resonance (27Al MAS NMR) spectroscopy, and mercury intrusion porosimetry (MIP) testing. The addition of alumina shortened the induction period, accelerated the acceleration period, and increased the mechanical strength of the PLC pastes with 3 and 7 wt% gypsum. The acceleration effect and strength enhancement were not distinct in the PLC pastes with less gypsum (0.1 wt%). The addition of γ-alumina led to the greatest accelerating effect and strength improvement in the PLC pastes with 3 and 7 wt% gypsum, and the compressive strength achieved was comparable to those of pure Ordinary Portland cement (OPC) pastes without limestone. The addition of γ-alumina induced the rapid dissolution of gypsum and consumption of sulfate ions. The chemical change affected by the addition of alumina varied greatly depending on the gypsum content, and trends in AFt and AFm formation in the PLC pastes with different gypsum contents were confirmed. Finally, pore size refinement was observed through the addition of alumina to PLC pastes with 3 and 7 wt% gypsum.

Fluorine in Complex Alumino-Boro-Silicate Glasses: Insight into Chemical Environment and Structure.

Fluorine incorporation into silicate glasses is important for technical fields as diverse as geophysics, extractive metallurgy, reconstructive dentistry, optical devices, and radioactive waste management. In this study, we explored the structural role of fluorine in alkaline alumino-borosilicate glass, with increasing amounts of fluorine up to 25 mol % F while maintaining the glass composition. Glasses were characterized by X-ray diffraction (XRD), 27Al and 19F magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy, and electron probe microanalysis. Results showed that essentially all F was retained; however, between 12 and 15 mol % F (∼3.6 and 4.5 wt % F), excess fluorine partitions to CaF2 and then NaF and Na-Al-F crystalline phases. Even prior to crystallization, there exist five distinct F sites, three of which evolve into crystalline phases. The two persistent glassy sites likely involve [4]Al-F-Ca/Na local structures. We propose a general understanding of the expected chemical shift of 19F NMR in systems containing Al, Ca, and Na.

Structural Insight into Protective Alumina Coatings for Layered Li-Ion Cathode Materials by Solid-State NMR Spectroscopy.

Layered transition metal oxide cathode materials can exhibit high energy densities in Li-ion batteries, in particular, those with high Ni contents such as LiNiO2. However, the stability of these Ni-rich materials often decreases with increased nickel content, leading to capacity fade and a decrease in the resulting electrochemical performance. Thin alumina coatings have the potential to improve the longevity of LiNiO2 cathodes by providing a protective interface to stabilize the cathode surface. The structures of alumina coatings and the chemistry of the coating-cathode interface are not fully understood and remain the subject of investigation. Greater structural understanding could help to minimize excess coating, maximize conductive pathways, and maintain high capacity and rate capability while improving capacity retention. Here, solid-state nuclear magnetic resonance (NMR) spectroscopy, paired with powder X-ray diffraction and electron microscopy, is used to provide insight into the structures of the Al2O3 coatings on LiNiO2. To do this, we performed a systematic study as a function of coating thickness and used LiCoO2, a diamagnetic model, and the material of interest, LiNiO2. 27Al magic-angle spinning (MAS) NMR spectra acquired for thick 10 wt % coatings on LiCoO2 and LiNiO2 suggest that in both cases, the coatings consist of disordered four- and six-coordinate Al-O environments. However, 27Al MAS NMR spectra acquired for thinner 0.2 wt % coatings on LiCoO2 identify additional phases believed to be LiCo1-xAlxO2 and LiAlO2 at the coating-cathode interface. 6,7Li MAS NMR and T1 measurements suggest that similar mixing takes place near the interface for Al2O3 on LiNiO2. Furthermore, reproducibility studies have been undertaken to investigate the effect of the coating method on the local structure, as well as the role of the substrate.

Effect of addition of LiAlSiO4 on microstructure, phase composition, and electrical properties of Li1.3Al0.3Ti1.7(PO4)3–based solid electrolyte

Li1.3Al0.3Ti1.7(PO4)3 (LATP) NASICON-type ceramic, due to its high bulk conductivity, is believed to be one of the most appropriate material for application as solid electrolyte in all-solid-state lithium-ion batteries. However, its highly resistant grain boundaries strongly limit the total ionic conductivity. Therefore, in this work, an attempt has been made to overcome this problem by introducing a Li-ion conducting additive LiAlSiO4 (LASO) to LATP base matrix in order to provide more conduction paths for lithium ions between grains. The properties of Li1.3Al0.3Ti1.7(PO4)3–xLiAlSiO4 (0.02 ≤ x ≤ 0.1) composite system were studied by means of: high-temperature X-ray powder diffractometry (HTXRD), 6Li, 27Al, and 31P magic angle spinning nuclear magnetic resonance spectroscopy (MAS NMR), scanning electron microscopy (SEM), and impedance spectroscopy (IS) methods. The obtained ceramic LATP–LASO materials exhibited high values of bulk conductivity, above 10−3 S/cm, and good total conductivity, exceeding 10−4 S/cm. The factors responsible for the enhancement, but also for the deterioration of total conductivity, i.e. microstructure and grain boundaries, are identified and discussed in this work.

Densification of sodium and magnesium aluminosilicate glasses at ambient temperature: structural investigations by solid-state nuclear magnetic resonance and molecular dynamics simulations.

Sodium and magnesium aluminosilicate glasses with compositions 20Na2O-20Al2O3-60SiO2 (NAS) and 20MgO-20Al2O3-60SiO2 (MAS) were subjected to a 12 and 25 GPa compression and decompression at room temperature, resulting in density increases from 3.7% to 5.3% (NAS) and from 8.2 to 8.4% (MAS), respectively. The pressurization at 25 GPa was done on 17O-enriched glasses, to facilitate characterization by 17O NMR. The structural changes associated with this process have been investigated by solid state 29Si, 27Al, 23Na, 25Mg, and 17O magic-angle spinning NMR and compared with the situation in thermally relaxed glasses and/or glasses prepared at ambient pressure. While in the Na aluminosilicate glass only subtle structural changes were observed in a sample densified at 12 GPa, the average coordination number of Al 〈CN(Al)〉 increases moderately from 4.00 to 4.26 by pressurization at 25 GPa. In the Mg-based system, 〈CN(Al)〉 increases from 4.34 to 4.57 to 4.83 in the sequence 10-4 GPa → 12 GPa → 25 GPa. The experimental result at 25 GPa was qualitatively confirmed by molecular dynamics (MD) simulations. Overall, pressurization results in more positive 29Si and 17O chemical shifts, most likely reflecting a reduction in the Si-O-Si and Si-O-Al bonding angles in the pressurized glasses. Furthermore, the results are also consistent with either an increased number of non-bridging O-atoms upon pressurization, or a larger number of Si-O-Al or Al-O-Al linkages. The significantly higher sensitivity of MAS, compared to NAS glass, to an increase in 〈CN(Al)〉 upon pressurization, provides a good structural rationale for its significantly higher crack initiation resistance.

Infrared transparent CaO–Ta2O5–Al2O3 glass-ceramics with high microhardness: Crystallization behavior and microstructure development

Infrared (IR) transparent materials with longer optical window and higher mechanical properties are highly demanded in optical communication, IR imaging, sensing and laser optics. Although transparent ceramics have higher mechanical strength, their production is still difficult using conventional sintering techniques. Herein, new IR transparent CaO–Ta2O5–Al2O3 glass-ceramics (TGCs) containing cubic ɑ-CaTa2O6 nanocrystals are reported. They exhibit a broadband transmitting window (0.5–5.5 μm) with high IR transmittance (∼80 %) and high refractive indices (nd = 1.96, n1530 = 1.93). The effects of heat treatment holding time on the structure and properties of TGCs are investigated. A slightly increased proportion of crystalline phase is determined by Rietveld refinement. 27Al magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy reveals that partial Al[4] and almost all Al[5] in the precursor glass are converted to Al[6] in the residual glass after crystallization. CaTa2O6 nanocrystals with amorphous shells are present within the nanodroplet domains, and a significant Ta enrichment is clearly observed. A confined crystallization process is proposed to understand the heat treatment time dependent structural characteristics and mechanical properties of the obtained TGCs. Vickers hardness (HV) of 12.01 GPa and Young's modulus (E) of 248.8 GPa are achieved in TGCs, making them promising candidates as high-performance IR materials for optical applications.

Conversion of methanol and ethanol into hydrocarbons over zeolites with different pore structure and acid properties

Methanol and ethanol are converted into hydrocarbons over zeolites with different pore structures and acid properties. It is an alternative technology for generating petrochemical feedstocks, particularly ethene and propene. Thus, the search for catalysts with physicochemical properties that maximize activity and selectivity to products of interest in the reaction has increased. In this study, ZSM-5 and MCM-22 zeolites in their acid form (HZSM-5 and HMCM-22), as well as ITQ-2, the delaminated form of MCM-22, were investigated as catalysts for methanol (MeOH) and ethanol (EtOH) conversion. All samples were characterized by X-ray diffractometry (XRD), X-ray fluorescence spectrometry (XRF), 27Al magic angle spinning nuclear magnetic resonance spectrometry (27Al MAS/NMR), N2 physisorption and temperature programmed desorption of ammonia (TPD of NH3). A comparison of the catalytic performance at 500 °C and atmospheric pressure showed that the product distribution and catalyst stability were significantly influenced by the studied alcohol, suggesting that these results reflected the differences in the mechanism for the formation of hydrocarbons.

Conversion of N-Acetylglucosamine to 3-Acetamido-5-Acetylfuran over Al-Exchanged Montmorillonite.

3-Acetamido-5-acetylfuran (3A5AF) is a potential platform compound for the production of nitrogen-containing pharmaceuticals and chemicals. 3A5AF can be obtained by dehydration of chitin or its monomer, N-acetylglucosamine (NAG). Here, we examined the use of solid catalysts for the dehydration of NAG to 3A5AF to achieve a more economical process that uses a recyclable catalyst. NAG was dehydrated using various solid catalysts in the presence of NaCl and N,N-dimethyl acetamide as solvent at 433 K. The yield of 3A5AF with the solid catalysts decreased in the following order: Al-exchanged montmorillonite>H-ZSM-5 (SiO2 /Al2 O3 =40)>H-montmorillonite (K-10)>Amberlyst15>H-ZSM-5 (SiO2 /Al2 O3 =300)>TiO2 >γ-Al2 O3 >ZrO2 >SiO2 ⋅ MgO>Na-montmorillonite. The highest yield of 3A5AF (14 %) was obtained with the Al-exchanged montmorillonite. The montmorillonite catalysts were characterized by using inductively coupled plasma optical emission spectroscopy, energy-dispersive X-ray spectroscopy, N2 adsorption, Fourier-transformed infrared spectroscopy, X-ray diffraction, and 27 Al magic-angle spinning nuclear magnetic resonance spectroscopy (MAS-NMR). In addition, a combined catalyst of Al-exchanged montmorillonite and Cl- from synthetic hydrotalcite was found to be an active and recyclable solid catalyst for NAG dehydration to 3A5AF.

Highly Efficient Decomposition of Perfluorocarbons for over 1000 Hours via Active Site Regeneration.

Tetrafluoromethane (CF4), the simplest perfluorocarbon (PFC), has the potential to exacerbate global warming. Catalytic hydrolysis is a viable method to degrade CF4, but fluorine poisoning severely restricts both the catalytic performance and catalyst lifetime. In this study, Ga is introduced to effectively assists the defluorination of poisoned Al active sites, leading to highly efficient CF4 decomposition at 600°C with a catalytic lifetime exceeding 1,000 hours. 27Al and 71Ga magic-angle spinning nuclear magnetic resonance spectroscopy (MAS NMR) showed that the introduced Ga exists as tetracoordinated Ga sites (GaIV), which readily dissociate water to form Ga-OH. In-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and density function theory (DFT) calculations confirmed that Ga-OH assists the defluorination of poisoned Al active sites via a dehydration-like process. As a result, the Ga/Al2O3 catalyst achieved 100% CF4 decomposition keeping an ultra-long catalytic lifetime and outperforming reported results. This work proposes a new approach for efficient and long-term CF4 decomposition by promoting the regeneration of active sites.

Local Structure and Mixed Proton-Hole Conduction in Y and Al-Doped BaZrO3

A mixed proton-hole conductor is expected to be an excellent cathode material for proton-conducting solid oxide fuel cells (PCFCs). Accepter-doped BaZrO3 has oxygen vacancies that can be either proton defects in wet or holes in oxidizing conditions. When both proton and hole concentrations are high enough, mixed proton-hole conduction is achieved. Our group has investigated the relationship between local structural distortion and hydration energy of accepter-doped BaZrO3. It was suggested that large Y3+ prefers the compensation by protonic defects; on the other hand, small Al3+ does holes or oxygen vacancies. Thus, by doping Y and Al into BaZrO3 simultaneously, high mixed proton-hole conduction is expected without transition metals. This study focuses on the local structure around dopants, especially around Al, which can be observed by nuclear magnetic resonance (NMR) spectroscopy. The coordination number of oxygen around Al can be converted to the number of oxygen vacancies. Based on the local structural analysis, the defect equilibrium and mixed conductivity of Y and Al co-doped BaZrO3 can be discussed. BaZr0.8Y0.2-xAlxO3-δ (BZYA) was prepared by solid-state reaction method. Proton concentration was evaluated by thermogravimetric analysis at 350 ºC. AC impedance measurement was performed to evaluate the electrical conductivity of BAYA in dry or wet Ar. The proton transport number was measured at 600 ºC using a water-vapor concentration cell. 27Al Magic-Angle Spinning (MAS) NMR was performed to investigate the configuration around Al. The proton concentration of BZY10A10 and BZY15A5 was 0.6 mol%, 1.8 mol%, respectively. These proton concentrations were much smaller than that of BZY20, 18.6 mol%. This indicates that Al substitution led to a decrease in proton concentration. Meanwhile, those BZYAs showed a relatively high proton transport number, 0.84. This was found to be due to the unique oxygen configuration around Al. The local structure around Al and its effect on proton concentration and mixed conduction will be discussed in the presentation.

Effect of Tetrahedrally Coordinated Al on the Surface Acidity of Mg-Al Binary Mixed Oxides.

Metal oxides (MOs) having Mg and Al with Mg/Al ratios of 1, 2, 3, and 4 were synthesized via calcination of the layered double hydroxides (LDH). The X-ray diffraction analysis revealed that all the MO consisted of periclase (MgO) crystallite with comparable crystallinity regardless of the metal ratio. According to the 27Al magic-angle spinning nuclear magnetic resonance, the phase transformation from LDH to MO upon calcination facilitated the evolution of the Al3+ ions with unsaturated coordination at the surface of MO. The specific surface area values of MOs were not significantly different from each other, ranging between 100 and 200 m2/g, suggesting that the metal ratio did not strongly influence the porous structure of MO. The temperature-dependent desorption of ammonia demonstrated that the Lewis acidity of the Al-rich MOs was the largest with an Mg/Al ratio of 1, attributed to the efficient exposure of the surface-active site Al3+-O2- pairs. The acidity of heterogenous Al-rich MOs significantly increased with the exposed tetrahedral Al site on the surface and dramatically diminished when the molar ratio (Mg/Al) was over two.

Structure, thermal properties and crystallization behavior of binary Y2O3–Al2O3 glasses with high alumina content

Five compositions in the system Al2O3–Y2O3 with high level of homogeneity were prepared in the form of glass microspheres by flame synthesis. The amorphous nature of prepared glasses with highly disordered structure was confirmed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman and nuclear magnetic resonance (NMR) spectroscopy. In the NMR spectra, typical signals with chemical shifts of 75, 42 and 12 ppm were observed, which were attributed to the presence of AlO4, AlO5 and AlO6 motifs in the glass structure. The ratio of individual motifs in glass samples did not change significantly with the composition. The crystallization of yttrium-aluminium garnet (YAG) phase was observed as a major process in the glasses thermally treated up to 1450 °C, with slow crystallization of θ- and α-Al2O3 phases detected in the temperature interval 980–1450 °C. IR and Raman spectra of the microspheres crystallized at 998, 1300 and 1500 °C for 4 h contained typical bands, that were assigned to the vibrations of AlO4 and AlO6 groups in YAG and Al2O3 structures. The comparison of 27Al and 89Y magic angle spinning (MAS) NMR spectra showed the presence of only YAG and α-Al2O3 phase in the samples crystallized at 1500 °C and the presence of a trace amount of θ-Al2O3 in the sample crystallized at 998 and 1300 °C. The yttrium aluminium perovskite (YAP) and yttrium aluminium monoclinic (YAM) phases, expected in this system, were no detected.

Mapping the structural trends in zinc aluminosilicate glasses.

The structure of zinc aluminosilicate glasses with the composition (ZnO)x(Al2O3)y(SiO2)1-x-y, where 0 ≤ x < 1, 0 ≤ y < 1, and x + y < 1, was investigated over a wide composition range by combining neutron and high-energy x-ray diffraction with 27Al magic angle spinning nuclear magnetic resonance spectroscopy. The results were interpreted using an analytical model for the composition-dependent structure in which the zinc ions do not act as network formers. Four-coordinated aluminum atoms were found to be in the majority for all the investigated glasses, with five-coordinated aluminum atoms as the main minority species. Mean Al-O bond distances of 1.764(5) and 1.855(5) Å were obtained for the four- and five-coordinated aluminum atoms, respectively. The coordination environment of zinc was not observed to be invariant. Instead, it is dependent on whether zinc plays a predominantly network-modifying or charge-compensating role and, therefore, varies systematically with the glass composition. The Zn-O coordination number and bond distance were found to be 4.36(9) and 2.00(1) Å, respectively, for the network-modifying role vs 5.96(10) and 2.08(1) Å, respectively, for the charge-compensating role. The more open coordination environment of the charge-compensator is related to an enhanced probability of zinc finding bridging oxygen atoms as nearest-neighbors, reflecting a change in the connectivity of the glass network comprising four-coordinated silicon and aluminum atoms as the alumina content is increased.

Spherical silica particles coated with lamellar nanocomposites based on a hydrophobic functionalized phyllosilicate

The surface of spherical silica particles (monodisperse, 2.6 µm) was modified with inorganic–organic lamellar ordered hybrids for applications as hydrophobic dye supports in cosmetics. The inorganic–organic multilayers comprised a 2:1 phyllosilicate (two sheets of linked SiO4 tetrahedra with one sheet of M2–3(OH)6 octahedra, where M is either magnesium or aluminum), consisting of octyl chains directly bonded to the inorganic sheets via Si–C covalent bonds. Octyltriethoxysilane was allowed to react at room temperature with spherical silica and aluminum acetylacetonate in a mixed aqueous solution of NaOH and NaCl at pH 10. The formation of a 2:1 phyllosilicate grafted with an octyl chain was confirmed by X-Ray powder diffraction, where a lamellar structure with the d001 value of 2.4 nm was displayed. The lamellar structure included the isomorphic substitution of Si by Al and the formation of C–Si–O–Aloct bonds, as shown in 29Si–and 27Al–magic angle spinning (MAS)–nuclear magnetic resonance (NMR) spectra. Further, the 23Na–MAS NMR spectrum indicated the incorporation of Na aquo complex cations into the organophyllosilicate. The hydrated Na ions were exchanged with a cationic dye (methylene blue) to be adsorbed. An anionic dye (Phloxine B), which has frequently been used as cosmetic pigments, was adsorbed onto the resulting hybrid particles when Al3+ was present in the dye solution. The hydrophobic dye supports can be used instead of plastic beads to reduce marine pollution.