Aluminum Alkoxide Research Articles

Transparent and high-porosity aluminum alkoxide network-forming glasses

Metal-organic network-forming glasses are an emerging type of material capable of combining the modular design and high porosity of metal-organic frameworks and the high processability and optical transparency of glasses. However, a generalizable strategy for achieving both high porosity and high glass-forming ability in modularly designed metal-organic networks has yet to be developed. Herein, we develop a series of aluminum alkoxide glasses and monoliths by linking aluminum-oxo clusters with alcohol linkers. A bulky monodentate alcohol modulator is introduced during synthesis and act as both network plasticizer and pore template, which can be removed by the subsequent solvent exchange to give gas accessible pores. Glasses synthesized with the modulator template exhibit well-defined glass transitions in their as-synthesized form and high surface areas up to 500 m2/g after activation, making them among the most porous glassy materials. The aluminum alkoxide glasses also have optical transparency and fluorescent properties, and their structures are elucidated by pair-distribution functions, spectroscopic and compositional analysis. These findings could significantly expand the library of microporous metal-organic network-forming glasses and enable their future applications.

Controlled engineering of high-purity pseudo-boehmite with large pore volume by aluminum alkoxide hydrolysis: Mechanistic understanding and reforming catalysis

The mechanistic understanding of the pore formation during aluminum alkoxide hydrolysis is of crucial importance for the controlled engineering of large pore volume pseudo-boehmite. The time-dependent structure evolution during n-hexanol-aluminum hydrolysis and the DFT calculations were performed to monitor the changes in the aluminum coordination. The results show that the hydrolysis, oxolation and alcoxolation reactions dominate the pore construction in turn with the continuous addition of water. The aluminum coordination undergoes aggregation from Al tetra-coordinates to Al hexa-coordinates and further stable Al3hexa-coordinates as repeating units for linear growth. The rate and amount of water injection is critical for the retention of at least one OR (R = -C6H13) group, which acts as a directed pore-forming group to promote the large cyclization growth of the Al3hexa-coordinates. Consequently, 1.44 cm3/g pore volume of high-purity pseudo-boehmite was obtained, and the prepared PtSn-Al2O3 catalyst exhibits a > 80 % of toluene selectivity for n-heptane reforming.

Study on Preparation Technology and Heat Conduction Mechanism of High-Purity & Ultra-Fine Alumina Powder from Scrap Aluminum Cans

In view of the increasing scarcity of bauxite resources in China, the high energy consumption and high pollution of electrolytic aluminum, and the requirements for energy conservation and environmental protection, aluminum recycling and high-value utilization of its derivatives have evolved into a crucial development requirement for the aluminum industry in the future. As an important part of the development of recycled aluminum resources, the high-value application of scrap aluminum cans has always been a hot research topic in various recycled aluminum processing enterprises and scientific research units. The traditional regeneration system of waste cans includes a series of complex technological processes such as pretreatment, paint removal, smelting system and casting system, which is difficult to control in the middle of the process. Most of the recycled scrap aluminum cans are cast and downgraded for later use, except for a part of them used as alloy materials for new cans. In this paper, combined with the research on the preparation of metal aluminum alkoxide, combined with recrystallization heat conduction to further study the effective dissolution or adsorption how to remove impurity elements to obtain high-purity aluminum alcohol salt mechanism research, and thermal effect of alcohols with different carbon chains on the synthesis of high-purity aluminum alkoxide was further investigated. Moreover, the changes in morphology and pore size distribution of hydrolyzed alumina precursor materials under different hydrothermal temperature conditions were discussed by means of the alkoxide hydrolysis-sol-gel process. Eventually, the aluminum alkoxide was obtained by the reaction of waste cans with isopropanol and heavy crystal thermal conductivity, and the high-purity aluminum alkoxide was purified by vacuum distillation. Under the hydrothermal condition of 160°C, the high-purity alumina material with a purity of 99.99% and an original crystal size of 200nm was prepared.

Chain extension epoxide polymerization to well‐defined block polymers using a N‐Al Lewis pair catalyst

AbstractBlock polyethers comprised of poly(propylene oxide) (PPO) and poly(ethylene oxide) (PEG or PEO) segments form the basis of ABA‐type PEO‐b‐PPO‐b‐PEO poloxamer materials. The inverse architecture with an internal hydrophilic PEO segment flanked by hydrophobic blocks can be difficult to prepare with control of architecture by use of traditional anionic polymerization. These oxyanionic polymerizations are plagued by chain‐transfer‐to‐monomer side reactions that occur with substituted epoxides such as propylene oxide (PO). Herein, we report a new method for the preparation of block polymers through a controlled polymerization involving a N‐Al Lewis adduct catalyst and an aluminum alkoxide macroinitiator. The Lewis pair catalyst was able to chain‐extend commercial PEO macroinitiators to prepare di‐, tri‐, and pentablock polyethers with low dispersity and reasonable monomer tolerance. Chain extension was confirmed using size exclusion chromatography and diffusion ordered nuclear magnetic resonance spectroscopy. The resulting block polymers were additionally analyzed with small‐angle X‐ray scattering to correlate the morphology to molecular architecture.

Ultrathin Flexible Encapsulation Materials Based on Al2O3/Alucone Nanolaminates for Improved Electrical Stability of Silicon Nanomembrane-Based MOS Capacitors.

Ultrathin flexible encapsulation (UFE) using multilayered films has prospects for practical applications, such as implantable and wearable electronics. However, existing investigations of the effect of mechanical bending strains on electrical properties after the encapsulation procedure provide insufficient information for improving the electrical stability of ultrathin silicon nanomembrane (Si NM)-based metal oxide semiconductor capacitors (MOSCAPs). Here, we used atomic layer deposition and molecular layer deposition to generate 3.5 dyads of alternating 11 nm Al2O3 and 3.5 nm aluminum alkoxide (alucone) nanolaminates on flexible Si NM-based MOSCAPs. Moreover, we bent the MOSCAPs inwardly to radii of 85 and 110.5 mm and outwardly to radii of 77.5 and 38.5 mm. Subsequently, we tested the unbent and bent MOSCAPs to determine the effect of strain on various electrical parameters, namely the maximum capacitance, minimum capacitance, gate leakage current density, hysteresis voltage, effective oxide charge, oxide trapped charge, interface trap density, and frequency dispersion. The comparison of encapsulated and unencapsulated MOSCAPs on these critical parameters at bending strains indicated that Al2O3/alucone nanolaminates stabilized the electrical and interfacial characteristics of the Si NM-based MOSCAPs. These results highlight that ultrathin Al2O3/alucone nanolaminates are promising encapsulation materials for prolonging the operational lifetimes of flexible Si NM-based metal oxide semiconductor field-effect transistors.

Cover Feature: Highly Electrophilic Mononuclear Cationic Aluminium Alkoxide Complexes: Syntheses, Reactivity and Catalytic Applications (Chem. Eur. J. 55/2023)

Cover Feature: Highly Electrophilic Mononuclear Cationic Aluminium Alkoxide Complexes: Syntheses, Reactivity and Catalytic Applications (Chem. Eur. J. 55/2023)

Highly Electrophilic Mononuclear Cationic Aluminum Alkoxide Complexes: Syntheses, Reactivity and Catalytic Applications.

Herein, we report on the synthesis of β-diketiminate supported aluminum complexes bearing terminal alkoxide and mono-thiol functional groups: LAlOMe(Et) (2), LAlOtBu(Et) (3), and LAlSH(Et) (4), (L= [HC{C(Me)N-(2,6-iPr2C6H3)}2]). Complexes 2 and 3 are further utilized as synthons to generate some fascinating cationic aluminum alkoxide complexes, [LAlOMe(µ-OMe)-Al(Et)L][EtB(C6F5)3] (5), [LAlOMe(OEt2)][EtB(C6F5)3] (6), and [LAlOtBu(OEt2)][EtB(C6F5)3] (8). These electrophilic cationic species are well characterized by spectroscopic and crystallographic techniques. The assessment of Lewis acidity by the Gutmann-Beckett method revealed superior Lewis acidity of the cations substituted with electron demanding alkoxy groups in comparison to the known methyl analogue [LAlMe][B(C6F5)4]. This has been further endorsed by computational calculations to determine the NBO charges and hydride ion affinity for complexes 6 and 8. These complexes are also capable of activating triethylsilane in stoichiometric reactions. The applicability of these complexes has been realized in the hydrosilylation of ethers, carbonyls, and olefines. Additionally, the solid state structure of a new THF stabilized aluminum halide cation [LAlCl(THF)][B(C6F5)4] (11) has also been reported.

Preparation of high permeability γ-Al2O3 ultrafiltration membranes from pseudo-boehmite industrial precursor

To obtain γ-Al2O3 ultrafiltration membranes, AlOOH sols which were usually derived from aluminum alkoxide were used as the top layer precursor. However, the colloidal sols obtained by this process were complex, high cost and time-consuming. Pseudo-boehmite, an industrial product with characteristics of high purity, excellent gelation and strong caking property, was widely used to prepare γ-Al2O3 products. In this work, mesoporous γ-Al2O3 ultrafiltration membranes were prepared conveniently and quickly by using pseudo-boehmite powder as precursor with colloidal sol-gel route at room temperature. The effects of H+/Al3+ molar ratio and polyvinyl alcohol (PVA) content on the properties of AlOOH sols and γ-Al2O3 ultrafiltration membranes were analyzed. Results showed that the viscosity and hydrodynamic particle diameter of the AlOOH sols can be controlled by changing the H+/Al3+ molar ratio, and the pore size of the prepared γ-Al2O3 ultrafiltration membranes could be varied by adjusting the PVA content in the AlOOH sols coating slurry. The pore size increased from 6.98 nm to 11.34 nm by increasing PVA content from 1.25% to 1.50%. Additionally, the γ-Al2O3 ultrafiltration membranes derived from the pseudo-boehmite exhibited a relatively high permeability (＞94.5 L m−2 h−1⋅MPa−1), which was higher than that of the aluminum alkoxide derived.

Silica-magnesium-titanium Ziegler–Natta catalysts. Part II. Properties of the active sites and fragmentation behaviour

In this work, which follows Part I that is dedicated to the precatalyst, we investigate the electronic properties and the accessibility of the Ti active sites in a highly active silica-supported Ziegler–Natta catalyst for industrial polyethylene production, applying a multi-scale, multi-technique approach. Complementary electronic spectroscopies (i.e. Ti K-edge XANES, Ti L2,3-edge NEXAFS and DR UV–Vis-NIR) reveal the coexistence of several titanium phases, whose relative amount depends on the concentration of the alkyl aluminum activator. In addition to β-TiCl3-like clusters and monomeric Ti(IV) sites, which are already present in the precatalyst, isolated Ti(III) sites and α-TiCl3-like clusters are formed in the presence of the activator. Two families of alkylated Ti(III) sites characterized by a different electron density are detected by IR spectroscopy of adsorbed CO, and two types of Ti-acyl species are formed upon CO insertion into the Ti-alkyl bond, characterized by a different extent of η2-coordination. The whole set of data suggests that TiCl3 clusters are preferentially formed at the exterior of the catalyst particles, likely as a consequence of Ti(III) mobility in the presence of strong Lewis acids, in most cases hampering the spectroscopic detection of isolated Ti(III) sites. In contrast, only monomeric Ti(III) sites are formed at the interior of the catalyst particles, characterized by a high electron density evocative of the presence of electron donors in the close proximity (e.g. aluminum alkoxide by-products). These sites are less accessible because of diffusion limitations, and only become visible by surface-sensitive spectroscopic methods (such as Ti L2,3-edge TEY-NEXAFS) upon the fragmentation of the catalyst particles.

Conversions in Silicon and Aluminum Alkoxide Gels during the Synthesis of Sialons as Probed by IR Spectroscopy

Conversions in Silicon and Aluminum Alkoxide Gels during the Synthesis of Sialons as Probed by IR Spectroscopy

Wear behavior and microstructure of alumina-mullite-zirconia composites prepared by a novel method: Coating of zircon powder by aluminum alkoxide

The formation of the mullite phase is the main challenge in the preparation of alumina-mullite-zirconia (AMZ) composites. To overcome this limitation, a novel method based on the coating of zircon powder with aluminum alkoxide was proposed in this study. Reaction sintering of alumina and coated zircon was carried out at 1630 °C for 3 h. The microstructural, physical, mechanical, and tribological properties of samples were compared with the conventional AMZ composites prepared by common mixing of alumina and zircon. The microstructural analysis indicated the higher alumina phase of the sample prepared with the conventional method. On contrary, the samples prepared with the proposed method included higher percentages of mullite phase. In terms of mechanical properties, the conventional AMZ samples performed better. However, due to the beneficial effect of the mullite phase in tribological applications, the samples prepared with this new method show superior wear resistance. Especially, the samples prepared from 30 wt% aluminum alkoxide exhibited the best wear resistance. The delamination and adhesive wear mechanisms govern the wear process.

Hydrothermal gasification of phenol with Ru added carbon-metal oxide composite-supported Ni catalysts prepared by sol-gel method

Ru promotion effect on carbon-metal oxide composite-supported Ni catalysts were tested for hydrothermal gasification of phenol in aqueous phase as a model process of wastewater treatment. The catalysts were prepared by the combination of aluminum, titanium and zirconium alkoxide, and polyethylene glycol as an organic template, with the addition of active metals, nickel nitrate hexahydrate and ruthenium chloride. In the hydrothermal gasification at 350 °C, pressure 20 MPa and phenol concentration in water 20 g/L, the effect of the addition of Ru to Ni/C/oxide was observed and the conversion of phenol increased. When the effect of metal oxide was compared at 5 wt% of Ru and 16 wt% of Ni contents, the conversion of phenol increased in the order ZrO2 < Al2O3 < TiO2. The activity of Al2O3 -supported catalysts increased with increasing Ru content while that of TiO2 -supported catalysts did not change with the Ru content.

Structurally characterized aluminum alkoxide derivatives for aerosol spray materials production

The synthesis of a family of aluminum alkoxides was undertaken via the reaction of trimethyl aluminum (Al(CH3)3) using a series of sterically varied ortho-substituted phenols (H-OAr), including: 2-methyl phenol (H-oMP), 2-isopropyl phenol (H-oPP), 2-phenyl phenol (H-oPhP), 2,6-di-methyl phenol (H-DMP), 2,6-di-isopropyl phenol (H-DIP), and 2,6-di-phenyl phenol (H-DPhP). The products isolated using the least sterically encumbered phenoxides proved to generate the homoleptic compounds: [(oMP)Al((μ-oMP)2Al(oMP)2)2] (1), and [Al(μ-oPP)(oPP)2]2 (2), [Al(μ-oPP)(oPP)2(THF)]2 (2-THF), and [Al(μ-oPhP)(oPhP)2]2 (3). As the steric bulk was increased only partial substitution was achieved forming the alkyl, alkoxide compounds: [Al(μ-OAr)(CH3)(OAr)]2 (OAr = trans-DMP (4a), cis-DIP (5a), trans-DPhP (6a)). Sub-stoichiometric metathesis reactions for the smaller OAr ligands were undertaken to produce a series of [Al(CH3)3-x(OAr)x]2 where × = 2: OAr = trans-oMP (1a); x = 1, OAr = oMP (1b), and DMP (4b). Alternatively, the use of neo-pentanol (H-ONep) led to the homoleptic species [(ONep)Al((μ-ONep)2Al(ONep)2)2] (7) and heteroleptic [Al(μ-ONep)(CH3)2]2 (7b). Efforts to generate 7 from [Al(OPri)3]4 resulted in the production of the mixed ligated species [Al4(μ-OPri)6(ONep)6] (8). The compounds were fully characterized using a variety of analytical tools as well as multinuclear NMR (1H, 13C, 27Al) spectroscopy. Select species were used for aerosol spray pyrolysis for the anticipated production of alumina (Al2O3) materials. The final products from 1, 1b, 7, and 7b proved to generate amorphous mesoparticles of size 2.1(0.1), 2.6(0.2), 2.7(0.2), and 2.5(0.2) μm, respectively as determined by SEM and pXRD analyses. Data collected using Single Particle Aerosol Mass Spectrometry (SPAMS) revealed that Al0 particles had been produced instead of the expected Al2O3 ceramic materials.

Synthesis and robocasting of YAG xerogel: one-step conversion of ceramics

An optimized sol–gel protocol was carried out to produce an yttrium aluminum garnet (YAG) xerogel from aluminum alkoxide and an yttrium salt on a semi-pilot scale. This xerogel was successfully used without prior pyrolysis as a solid load with the aid of additives in the preparation of pastes. Thermal treatment of the green bodies, obtained by robocasting of the paste, led to cohesive single-phase YAG ceramics. Manufacturing ceramic pieces by additive methods will allow shaping complex forms, while the single step conversion/consolidation would simplify the technological process, reducing global energy costs. Since YAG possesses high strength and good creep behavior at high temperatures, these refractory pieces could replace the metal alloys used in turbine blades for deep space exploration. Structural, thermal and chemical characterizations were performed on xerogel powders, pastes, and YAG ceramics.

Compound surfactant-based emulsion method for the preparation of high-porosity alumina microspheres

Porous alumina microspheres have attracted significant attention owing to their high mechanical strength and excellent chemical and thermal stability. The emulsion method is considered as a simple and controllable method for the preparation of inorganic microspheres. However, preparing alumina microspheres with the emulsion method is challenging because the emulsification of the precursor is inhibited by the rapid hydrolysis of aluminum alkoxide. Herein, we report a new emulsion method for the preparation of high-porosity alumina microspheres using a combination of ionic and non-ionic surfactants; in this method, the compound surfactants act as a template agent to guide aluminum alkoxide to form a lamellar structure through self-assembly. The decomposition of the templating agent and transformation of the alumina crystal at a high temperature result in structural collapse and formation of lamellar pores. Compound surfactants increased the spheroidization rate of the emulsion from 47% to 63% after hydrolysis, whereas the particle size was decreased by almost half. Additionally, the morphology and porosity of the alumina microspheres were changed. With increasing anionic surfactant content, the porosity increased initially and then decreased. The porosity of the alumina microspheres reached a maximum value of 76% at the 1:1 mass ratio of the non-ionic to anionic surfactants. Heat treatment was found to change the size of lamellar pores, with the pore diameter reaching maximum value at 1300 °C. The compound surfactants also increased the compressive stress and specific surface area of the porous alumina microspheres.

Organic/inorganic double-precursor cross-linked alumina aerogel with high specific surface area and high-temperature resistance

Alumina aerogel has drawn a great research interest in the aerogel community owing to its great high-temperature heat resistance. The typical preparation can be divided into two approaches depending on the type of precursors. However, the alumina aerogel derived from organic aluminum alkoxides suffers from poor monolithic integrity, whereas the one from inorganic aluminum salts presents unsatisfied thermal stability. In this work, we develop a novel organic/inorganic double-precursor cross-linking method to prepare alumina aerogels. Aluminum chloride hexahydrate is used to provide an acid condition for the hydrolysis and condensation reaction of aluminum sec-butoxide (ASB), and serves as a reactant to co-condensate with the hydrolyzed ASB to form an interpenetrating chain structure. The resulting alumina aerogel exhibits a high specific surface area (SSA) of 667 m2/g and good high-temperature thermal insulation performance. Moreover, it can still retain SSA of 224 and 105 m2/g after heating at 1000 and 1300°C, respectively.

Elaboration of porous alumina nanofibers by electrospinning and molecular layer deposition for organic pollutant removal

The development of heterogeneous nanomaterials with high surface to volume ratio is crucial for enhancing the adsorption of water pollutants, such as toxic organic dyes. Here, we describe the synthesis of polyacrylonitrile (PAN) nanofibers coated with porous alumina nanolayers, and their application for adsorption of the organic dye methylene blue (MB). First, we produced PAN nanofibers by electrospinning, and then coated them with an aluminum alkoxide hybrid films fabricated using molecular layer deposition. Finally, we used thermal annealing to obtain the final PAN nanofibers coated with porous alumina nanolayers. We characterized the obtained nanostructured materials by scanning electron microscopy, transmission electron microscopy, N 2 desorption/adsorption porosimetry (BET theory), and Fourier-transform infrared spectroscopy. The porous nanomaterials had a surface area of 631.79 m 2 /g that allowed reaching an adsorption efficiency of 88% with 10 ppm MB. The adsorption kinetics and isotherms were better described by a pseudo-first-order model and the Langmuir adsorption model, respectively, based on physical adsorption (monolayer adsorption) of the adsorbed molecules. • Alucone Hybrid polymeric thin films grown on PAN nanofibers prepared by MLD route using TMA and EG as precursors. • Hybrid alucone polymeric thin films annealed in air gives a Mesoporous structure of Al 2 O 3 with a surface area of 631.8 m 2 /g. • Adsorption efficiency of 88% for 10 ppm MB dye concentration was reached due to high porosity of the alumina structure. • The adsorption of MB onto alucone is a monolayer adsorption process confirmed by the Langmuir model.

First Principles Modelling of Growth of Alucone Thin Films from Aromaticalcohol and Amine Precursors

Hybrid materials composed of organic and inorganic components offer the opportunity to develop interesting materials with well-controlled properties. Molecular Layer Deposition (MLD) is a suitable technique for the controlled growth of thin, conformal hybrid films. Despite growing interest in these materials, there is, however, insufficient understanding of the atomistic mechanism of MLD film growth.In this contribution, we present a first principles investigation of the molecular mechanism of the growth of hybrid organic−inorganic thin films of aluminium alkoxides, known as ”alucones”, grown by MLD. We investigate in detail the chemistry of the MLD process between the post-TMA pulse methyl-terminated Al2O3 surface and the homo- or hetero- bifunctional aromatic compounds with hydroxy and/or amino groups as reactive groups: hydroquinone (HQ), 4-aminophenol (AP) and p-phenylenediamine (PDA). Double reactions of HQ, AP and PDA with the alumina surface are explored in detail to assist the interpretation of the experimental findings regarding the differences in alucone films grown with HQ, AP and PDA. DFT calculations show that all aromatic precursor molecules bind favorably to the methyl terminated Al2O3, via formation of Al-O and Al-N bonds and CH4 elimination. However, reaction energetics suggest lower reactivity of the amino groups with TMA in comparison to the hydroxyl groups. Therefore, we expect that in the case of the heterobifunctional precursor, AP, for which one of the groups is more reactive (OH) than the other (NH2), the unwanted double surface reactions are reduced and the organic molecule can be self-assembled in a more up-right configuration, which leads to higher growth per rates. We also analyze the reactions between the methyl-terminated Al2O3 with 2-methylhydroquinone, 2-methoxyhydroquinone, 2-chlorhydroquinone and 2-nitrohyrdoquinone to examine the influence of the activating groups –CH3, -OCH3 and deactivating groups –Cl and –NO2 on the interaction between the O site of the organic molecule and the Al site of TMA. This study contributes to the understanding of growth process of HQ-alucones, AP-alucones and PDA-alucones at the molecular level and is valuable in supporting experimental data on hybrid film growth.

Different approaches to obtain functionalized alumina as additive in polymer electrolyte membranes

A series of sulfated aluminum oxides (S-Al2O3), investigated as an electrolyte additive in Nafion membranes, was synthesized via three different methods: (i) sol–gel sulfation starting from an aluminum alkoxide precursor, (ii) room temperature sulfation of fumed aluminum oxide, and (iii) hydrothermal sulfation of fumed aluminum oxide. Through the characterization of the synthesized S-Al2O3 by means of X-ray diffraction (XRD), thermogravimetric analysis (TGA), and infrared (IR) spectroscopy, a higher sulfation rate was found to be achieved via a hydrothermal sulfation, and the coordination state of sulfate groups was identified as monodentate. By using this hydrothermally synthesized S-Al2O3 as additive, a composite Nafion-based membrane was realized and compared to plain Nafion, by means of thermal analyses and fuel cell tests. Although higher hydration degree was found for the undoped membrane by differential scanning calorimetry (DSC), improved retention of fuel cell performance upon the increase of operation temperature was observed by using the composite electrolyte, confirming the stabilizing effect of the acidic inorganic additive.

Nitrogenation Conditions for Mixed Silicon and Aluminum Alkoxide Xerogels

Nitrogenation Conditions for Mixed Silicon and Aluminum Alkoxide Xerogels