Understanding the Effect Models of Ionic Liquids in the Synthesis of NH4‐Dw and γ‐AlOOH Nanostructures and Their Conversion into Porous γ‐Al2O3

Well‐dispersed ammonium aluminum carbonate hydroxide (NH₄‐Dw) and γ‐AlOOH nanostructures with controlled morphologies have been synthesized by employing an ionic‐liquid‐assisted hydrothermal process. The basic strategies that were used in this work were: 1) A controllable phase transition from NH₄‐Dw to γ‐AlOOH could be realized by increasing the reaction temperature and 2) the morphological evolution of NH₄‐Dw and γ‐AlOOH nanostructures could be influenced by the concentration of the ionic liquid. Based on these experimental results, the main objective of this work was to clarify the effect models of the ionic liquids on the synthesis of NH₄‐Dw and γ‐AlOOH nanostructures, which could be divided into cationic‐ or anionic‐dominant effect models, as determined by the different surface structures of the targets. Specifically, under the cationic‐dominant regime, the ionic liquids mainly showed dispersion effects for the NH₄‐Dw nanostructures, whereas the anionic‐dominant model could induce the self‐assembly of the γ‐AlOOH particles to form hierarchical structures. Under the guidance of the proposed models, the effect of the ionic liquids would be optimized by an appropriate choice of cations or anions, as well as by considering the different effect models with the substrate surface. We expect that such effect models between ionic liquids and the target products will be helpful for understanding and designing rational ionic liquids that contain specific functional groups, thus open up new opportunities for the synthesis of inorganic nanomaterials with new morphologies and improved properties. In addition, these as‐prepared NH₄‐Dw and γ‐AlOOH nanostructures were converted into porous γ‐Al₂O₃ nanostructures by thermal decomposition, whilst preserving the same morphology. By using HRTEM and nitrogen‐adsorption analysis, the obtained γ‐Al₂O₃ samples were found to have excellent porous properties and, hence, may have applications in catalysis and adsorption.     

Microporous Crystalline γ‐Al2O3 Replicated from Microporous Covalent Triazine Framework and Its Application as Support for Catalytic Hydrolysis of Ammonia Borane

Significant progress has been made on the synthesis and application of mesoporous γ‐alumina. To date, little attention has been paid to the synthesis of microporous crystalline alumina. Here, fabrication of microporous crystalline γ‐alumina using a microporous covalent triazine framework (CTF‐1) as a template is described. Microporous crystalline γ‐alumina with a micro‐meso binary pore system was replicated by infiltration of aluminum nitrate into the micropores of the CTF‐1 template through a NH₃/water‐vapor‐induced internal hydrolysis method, followed by thermal treatment, and subsequent removal of the CTF‐1 template with a 30 % H₂O₂ aqueous solution. The obtained crystalline γ‐alumina material exhibits a large surface area (349 m² g⁻¹) with micropore distribution centered at about 1.27 nm. Ru supported on microporous γ‐Al₂O₃ can be employed as catalyst for hydrolytic dehydrogenation of ammonia borane, and it exhibits high catalytic activity and good durability. This finding provides a new benchmark for preparing well‐defined crystalline microporous alumina materials by a template method, which can be applied in a wide range of fields.     

Mesoporous Core–Shell Fenton Nanocatalyst: A Mild,Operationally Simple Approach to the Synthesis of Adipic Acid

Mesoporous nanoparticles composed of γ‐Al₂O₃ cores and α‐Fe₂O₃ shells were synthesized in aqueous medium. The surface charge of γ‐Al₂O₃ helps to form the core–shell nanocrystals. The core–shell structure and formation mechanism have been investigated by wide‐angle XRD, energy‐dispersive X‐ray spectroscopy, and elemental mapping by ultrahigh‐resolution (UHR) TEM and X‐ray photoelectron spectroscopy. The N₂ adsorption–desorption isotherm of this core–shell materials, which is of type IV, is characteristic of a mesoporous material having a BET surface area of 385 m² g^?1 and an average pore size of about 3.2 nm. The SEM images revealed that the mesoporosity in this core–shell material is due to self‐aggregation of tiny spherical nanocrystals with sizes of about 15–20 nm. Diffuse‐reflectance UV/Vis spectra, elemental mapping by UHRTEM, and wide‐angle XRD patterns indicate that the materials are composed of aluminum oxide cores and iron oxide shells. These Al₂O₃@Fe₂O₃ core–shell nanoparticles act as a heterogeneous Fenton nanocatalyst in the presence of hydrogen peroxide, and show high catalytic efficiency for the one‐pot conversion of cyclohexanone to adipic acid in water. The heterogeneous nature of the catalyst was confirmed by a hot filtration test and analysis of the reaction mixture by atomic absorption spectroscopy. The kinetics of the reaction was monitored by gas chromatography and ¹H NMR spectroscopy. The new core–shell catalyst remained in a separate solid phase, which could easily be removed from the reaction mixture by simple filtration and the catalyst reused efficiently.     

Structure Modification Function of g‐C3N4 for Al2O3 in the In Situ Hydrothermal Process for Enhanced Photocatalytic Activity

Heterojunctions of g‐C₃N₄/Al₂O₃ (g‐C₃N₄=graphitic carbon nitride) are constructed by an in situ one‐pot hydrothermal route based on the development of photoactive γ‐Al₂O₃ semiconductor with a mesoporous structure and a high surface area (188 m²g^?1) acting as electron acceptor. A structure modification function of g‐C₃N₄ for Al₂O₃ in the hydrothermal process is found, which can be attributed to the coordination between unoccupied orbitals of the Al ions and lone‐pair electrons of the N atoms. The as‐synthesized heterojunctions exhibit much higher photocatalytic activity than pure g‐C₃N₄. The hydrogen generation rate and the reaction rate constant for the degradation of methyl orange over 50 % g‐C₃N₄/Al₂O₃ under visible‐light irradiation (λ>420 nm) are 2.5 and 7.3 times, respectively, higher than those over pristine g‐C₃N₄. The enhanced activity of the heterojunctions is attributed to their large specific surface areas, their close contact, and the high interfacial areas between the components as well as their excellent adsorption performance, and efficient charge transfer ability.     

Microwave‐Assisted Hydrothermal Synthesis of [Al(OH)(1,4‐NDC)] Membranes with Superior Separation Performances

In this study, we report a facile ligand‐assisted in situ hydrothermal approach for preparation of compact [Al(OH)(1,4‐NDC)] (1,4‐NDC=1,4‐naphthalenedicarboxylate) MOF membranes on porous γ‐Al₂O₃ substrates, which also served as the Al³⁺ source of MOF membranes. Simultaneously, it was observed that the heating mode exerted significant influence on the final microstructure and separation performance of [Al(OH)(1,4‐NDC)] membranes. Compared with the conventional hydrothermal method, the employment of microwave heating led to the formation of [Al(OH)(1,4‐NDC)] membranes composed of closely packed nanorods with superior H₂/CH₄ selectivity.     

Location of the Spinel Vacancies in γ‐Al2O3

A non‐spinel model for the structure of γ‐Al₂O₃, with 25 % of the Al³⁺ cations at tetrahedral positions, has been the subject of wide interest. However, ¹⁷O NMR measurements and, more recently, ²⁷Al NMR measurements have shown that there are considerably more Al³⁺ cations at tetrahedral positions. This means that the Al³⁺ vacancies in γ‐Al₂O₃ are not at tetrahedral but at octahedral positions, as in isostructural γ‐Fe₂O₃ and in accordance with density functional theory predictions. This has consequences with regard to the surface structure of γ‐Al₂O₃, and thus, for catalysis.     

Synthesis,characterization and single crystal structure determination of aluminum alkoxydisilanolates: precursors for silica–alumina composite

Several novel aluminum alkoxydisilanolate complexes were prepared by reaction of triphenylsilanol with aluminum 2‐methoxyethoxide, aluminum 2‐ethoxyethoxide, aluminum sec‐butoxide and aluminum iso‐propoxide. All new complexes, [(Ph₃SiO)₂Al(OR)]₂ [where R = CH₂CH₂OCH₃ (1), CH₂CH₂OC₂H₅ (2), CH(CH₃)CH₂CH₃ (3) and CH(CH₃)₂ (4)] were characterized by elemental analysis, mass spectrometry and infrared spectroscopy (IR), as well as ¹H, ¹³C, ²⁹Si and ²⁷Al NMR spectroscopies. The solid‐state structures of the representative compound 2 and 4 were also verified by single‐crystal X‐ray analyses. Complexes 2 and 4 are dimers having distorted trigonal bipyramidal and tetrahedral coordination at the aluminum center, respectively. The ²⁷Al NMR spectrum of compound 2 showed that the solid‐state structure of the complex was not retained in solution, and tetracoordinated aluminum was found in solution in contrast to the pentacoordinated geometry in the solid state. The hydrothermal treatment of 1 and 4 at 200 °C and the subsequent calcination at 1000 °C resulted in the formation of alumina–silica composite (4SiO₂·Al₂O₃) with γ‐alumina in the silica matrix. Copyright © 2010 John Wiley & Sons, Ltd.     

The effect of iron phosphate,alumina and silica coatings on the morphology of carbonyl iron particles

Carbonyl iron powders were coated with iron phosphate using phosphating method and boehmite (γ‐AlOOH) or silicon hydroxide (Si(OH)₄) nanoparticles derived from the hydrolysis of tri‐sec‐butoxide (Al(OC₄H₉)₃) or tetramethylsilane (Si(OCH₃)₄) using sol–gel method. The coated powders were dried and calcined at 400 °C for 3 h in air. Cross‐section morphology of coated carbonyl iron powders were investigated by scanning electron microscopy energy dispersive X‐ray analysis. Coated Fe micro‐particles were spherical in shape with ‘shell/core’ structures. The shells consisted of an amorphous layer with varying thickness (100–800 nm) and the core represented a carbonyl iron. Gelatinous morphology of dried FePO₄ coating composed from nanoparticles of iron oxyhydroxides and hydrated iron phosphate with a shell thickness of ～100 nm around iron particles was observed. In coatings based on alumina or silica xerogels with a thickness of ～100–150 nm or ～200–500 nm, the coatings were composed of iron oxyhydroxides and γ‐AlOOH or Si(OH)₄. The resulting XRD diffractograms revealed the hematite (α‐Fe₂O₃) and magnetite (Fe₃O₄) that were formed in phosphated and sol–gel coated iron powders. The X‐ray diffraction patterns did not verify the presence of phosphates, alumina or silica and indicate the amorphous or nanocrystalline structure of FePO₄, γ‐Al₂O₃ and SiO₂. Copyright © 2009 John Wiley & Sons, Ltd.     

Controllable Synthesis of Mesoporous Iron Oxide Nanoparticle Assemblies for Chemoselective Catalytic Reduction of Nitroarenes

Iron(III) oxide is a low‐cost material with applications ranging from electronics to magnetism, and catalysis. Recent efforts have targeted new nanostructured forms of Fe₂O₃ with high surface area‐to‐volume ratio and large pore volume. Herein, the synthesis of 3D mesoporous networks consisting of 4–5 nm γ‐Fe₂O₃ nanoparticles by a polymer‐assisted aggregating self‐assembly method is reported. Iron oxide assemblies obtained from the hybrid networks after heat treatment have an open‐pore structure with high surface area (up to 167 m² g^?1) and uniform pores (ca. 6.3 nm). The constituent iron oxide nanocrystals can undergo controllable phase transition from γ‐Fe₂O₃ to α‐Fe₂O₃ and to Fe₃O₄ under different annealing conditions while maintaining the 3D structure and open porosity. These new ensemble structures exhibit high catalytic activity and stability for the selective reduction of aryl and alkyl nitro compounds to the corresponding aryl amines and oximes, even in large‐scale synthesis.     

Efficient conversion of fructose to 5‐hydroxymethylfurfural by functionalized γ‐Al2O3 beads

Millimeter size γ‐Al₂O₃ beads were prepared by alginate assisted sol–gel method and grafting organic groups with propyl sulfonic acid and alkyl groups as functionalized γ‐Al₂O₃ bead catalysts for fructose dehydration to 5‐hydroxymethylfurfural (5‐HMF). Experiment results showed that the porous structure of γ‐Al₂O₃ beads was favorable to the loading and dispersion of active components, and had an obvious effect on the properties of the catalyst. The lower calcination temperature of γ‐Al₂O₃ beads increased the specific surface area, the hydrophobicity and the activity of catalysts. Competition between the reaction of alkyl groups and ‐SH groups with surface hydroxyl during the preparation process of the catalyst influenced greatly the acid site densities, hydrophobic properties and activity of the catalyst. With an increase in the alkyl group chain, the hydrophobicity of catalysts increased obviously and the activity of the catalyst was enhanced. The most hydrophobic catalyst C₁₆‐SO₃H‐γ‐Al₂O₃–650°C exhibited the highest yield of 5‐HMF (84%) under the following reaction conditions: reaction medium of dimethylsulfoxide/H₂O (V/V, 4:1), catalyst amount of 30 mg, temperature of 110°C and reaction time of 4 hr.     

The influence of initial surface conditions on field crystallization of anodic aluminum oxide films determined by synchrotron X‐ray diffraction

X‐ray diffraction measurements were performed using synchrotron radiation at the SPring‐8 facility and electrochemical techniques to investigate the effect of polishing methods and storage conditions on the crystal structure of air‐formed oxide films and anodic oxide films formed on highly pure aluminum. Storage in an N₂ environment hinders local film breakdown during anodizing, and it was established that the X‐ray diffraction measurements showed the presence of a γ‐Al₂O₃ in the anodic oxide film formed on mechanically polished (MP) specimens. Formation of γ‐Al₂O₃ during anodizing was inhibited by electropolishing because of the removal of the work‐hardened layer that was formed on the MP by electro‐polishing. The X‐ray diffraction results do not show clear differences in the influence of the polishing method on the crystal structure of air formed oxide film. This is due to the very fast oxidation rate of the air‐formed oxide film and very long storage times for the X‐ray measurements. The anodic oxide film formed on aluminum, which has a very flat surface, shows color and the color depended on grain orientation. The electrochemical impedance of the MP specimen is slightly lower than that of the mechanically and then electrochemically polished specimen at the middle frequency range. This impedance difference may be due to formation of γ‐Al₂O₃ in the amorphous anodic oxide film and the thickness of the film. Copyright © 2010 John Wiley & Sons, Ltd.     

Effect of Hydrothermal on the Crystalline Phase and Morphology of Manganese Oxide Nanocrystals

The effect of hydrothermal on the crystalline phase and morphology of manganese oxide nanocrystals was studied. The Mn₃O₄ nanoparticles were transformed into γ‐MnOOH nanowires after hydrothermal treatment. The pH plays an important role in the transformation of crystalline phases. The whole nanowires of γ‐MnOOH were formed at pH 8 and pH 9 while the crystalline phase of Mn₃O₄ was still remained in the mixture of Mn₃O₄ and γ‐MnOOH at pH 10.     

A New Method of Synthesis of Nanosized Boehmite (AlOOH) Powders with a Low Impurity Content

A new method of synthesis of nanosized aluminum oxyhydroxide (AlOOH, boehmite) powders has been suggested through a hydrothermal treatment of nanosized γ-Al₂O₃ powder in water and a 1.5 wt % HCl solution at different temperatures. It has been found that hydrothermal treatment in a 1.5 wt % HCl solution leads to the purification of the starting material; different treatment durations allow one to obtain boehmite particles of different shape. It has been demonstrated that a nanosized boehmite powder is obtained upon the hydrothermal treatment of a nanosized γ-Al₂O₃ in water above 80°С. The nanosized boehmite powders synthesized at different temperatures have been studied by various methods.     

Fe K‐Edge X‐ray Absorption Fine Structure Determination of γ‐Al2O3‐Supported Iron‐Oxide Species

The structure of FeO_x species supported on γ‐Al₂O₃ was investigated by using Fe K‐edge X‐ray absorption fine structure (XAFS) and X‐ray diffraction (XRD) measurements. The samples were prepared through the impregnation of iron nitrate on Al₂O₃ and co‐gelation of aluminum and iron sulfates. The dependence of the XRD patterns on Fe loading revealed the formation of α‐Fe₂O₃ particles at an Fe loading of above 10 wt %, whereas the formation of iron‐oxide crystals was not observed at Fe loadings of less than 9.0 wt %. The Fe K‐edge XAFS was characterized by a clear pre‐edge peak, which indicated that the Fe?O coordination structure deviates from central symmetry and that the degree of Fe?O?Fe bond formation is significantly lower than that in bulk samples at low Fe loading (<9.0 wt %). Fe K‐edge extended XAFS oscillations of the samples with low Fe loadings were explained by assuming an isolated iron‐oxide monomer on the γ‐Al₂O₃ surface.     

Synthesis and Characterization of Spinel‐Type Gallia‐Alumina Solid Solutions

By precipitation with ammonia of ethanolic solutions containing the appropriate proportions of gallium and aluminium nitrate, following by calcination of the resulting gels at 773 K, mixed Ga₂O₃/Al₂O₃ oxides having Ga:Al ratios of 9:1, 4:1, 1:1, 1:4 and 1:9 were obtained. Powder X‐ray diffraction showed that these mixed metal oxides form a series of solid solutions having the spinel‐type structure; also shown by γ‐Al₂O₃ and γ‐Ga₂O₃. The specific surface area (determined by nitrogen adsorption at 77 K) was found to range from 160 m² g^?1 for the mixed oxide having Ga:Al = 9:1 up to 370 m² g^?1 for that having Ga:Al = 1:9. High resolution MAS NMR showed that Ga³⁺ and Al³⁺ ions occur at both tetrahedral and octahedral sites in the spinel‐type structure of the mixed metal oxides, although there is a preferential occupation of tetrahedral sites by Ga³⁺ ions. A proportion of penta‐coordinated Al³⁺ ions was also found. IR spectra of carbon monoxide adsorbed at 77 K showed that the mixed metal oxides have a considerable Lewis acidity, related mainly to tetrahedrally coordinated metal ions exposed at crystal surfaces. The characteristic infrared absorption band of coordinated (adsorbed) CO appears in the range 2205–2190 cm^?1, and its peak wavenumber is nearly independent of Ga:Al ratio in the mixed gallia‐alumina oxides.     

Efficient Noble‐Metal‐Free γ‐Fe2O3@NiO Core–Shell Nanostructured Photocatalysts for Water Oxidation

Flowerlike noble‐metal‐free γ‐Fe₂O₃@NiO core–shell hierarchical nanostructures have been fabricated and examined as a catalyst in the photocatalytic oxidation of water with [Ru(bpy)₃](ClO₄)₂ as a photosensitizer and Na₂S₂O₈ as a sacrificial electron acceptor. An apparent TOF of 0.29 μmols^?1 m^?2 and oxygen yield of 51 % were obtained with γ‐Fe₂O₃@NiO. The γ‐Fe₂O₃@NiO core–shell hierarchical nanostructures could be easily separated from the reaction solution whilst maintaining excellent water‐oxidation activity in the fourth and fifth runs. The surface conditions of γ‐Fe₂O₃@NiO also remained unchanged after the photocatalytic reaction, as confirmed by X‐ray photoelectron spectroscopy (XPS).     

Engineered mesoporous ionic‐modified γ‐Fe2O3@hydroxyapatite decorated with palladium nanoparticles and its catalytic properties in water

A new mesoporous organic–inorganic nanocomposite was formulated and then used as stabilizer and support for the preparation of palladium nanoparticles (Pd NPs). The properties and structure of Pd NPs immobilized on prepared 1,4‐diazabicyclo[2.2.2]octane (DABCO) chemically tagged on mesoporous γ‐Fe₂O₃@hydroxyapatite (ionic modified (IM)‐MHA) were investigated using various techniques. The synergistic effects of the combined properties of MHA, DABCO and Pd NPs, and catalytic activity of γ‐Fe₂O₃@hydroxyapatite‐DABCO‐Pd (IM‐MHA‐Pd) were investigated for the Heck cross‐coupling reaction in aqueous media. The appropriate surface area and pore size of mesoporous IM‐MHA nanocomposite can provide a favourable hard template for immobilization of Pd NPs. The loading level of Pd in the nanocatalyst was 0.51 mmol g^?1. DABCO bonded to the MHA surface acts as a Pd NP stabilizer and can also lead to colloidal stability of the nanocomposite in aqueous solution. The results reveal that IM‐MHA‐Pd is highly efficient for coupling reactions of a wide range of aryl halides with olefins under green conditions. The superparamagnetic nature of the nanocomposite means that the catalyst to be easily separated from solution through magnetic decantation, and the catalytic activity of the recycled IM‐MHA‐Pd showed almost no appreciable loss even after six consecutive runs.     

Sorption—desorption studies of anionic dyes on alumina pretreated with acids

Sorption—desorption behaviour of the anionic dyes naphthol blue-black (NB) and lissamine green ‘BN’ (LG) on chromatographic alumina, pretreated with mineral acids, is described. Alumina samples of surface-phase pH 1.0–8.0 were prepared and studied for their sorption behaviour. The sorption was found to vary with surface pH of the substrate and acid used for pretreatment. Quantitative sorption was shown at pH ⩽ 4.0 (NB) and pH ⩽ 3.5 (LG) on Al₂O₃ treated with HNO₃ [Al₂O₃(n)], and maximum sorption occurred at pH 5.0 (NB) and pH 5.5 (LG) on Al₂O₃ treated with H₂SO₄ [Al₂O₃(s)] and pH 2.5 (NB) and pH 3.0 (LG) on Al₂O₃ treated with H₃PO₄ [Al₂O₃(p)]. Variation in sorption with time (10 min-72, h), temperature (30–60°C) and regeneration of the substrates with aqueous electrolytes is also reported. Desorption efficacy of anions was in the order: PO³⁻₄ > SO²⁻₄ > NO⁻₃. The acid-treatment, and hence the specifically adsorbed anions (NO⁻₃, SO²⁻₄, PO³⁻₄), appears to modify the sorption properties of alumina significantly. It appears that the controlling force for adsorption is predominantly ion exchange. A few synthetic mixtures of the dyes were separated by column chromatography, using inorganic electrolytes as eluents.     

Kinetics of the uptake of SO2 on mineral oxides: Improved initial uptake coefficients at 298 K from pulsed Knudsen cell experiments

The uptake of SO₂ on γ‐Fe₂O₃, γ‐Al₂O₃, and Saharan dust has been studied at T = 298 K using a Knudsen cell reactor operated in a steady‐state as well as in a pulsed mode. The initial uptake coefficients determined in the steady‐state mode have been found to be affected by surface saturation as well as bulk diffusion of SO₂ resulting in an apparent dependence of the initial uptake coefficients on the sample mass of the mineral oxides. However, by operating the Knudsen cell in the pulsed mode with shorter response time, these effects could be suppressed. Initial uptake coefficients of γ_ini (Fe₂O₃) = (8.8 ± 0.4) × 10^?2, γ_ini (Al₂O₃) = (7.4 ± 0.9) × 10^?3, and γ_ini (Saharan dust) = (7.6 ± 0.5) × 10^?2 were derived. This suggests that Fe₂O₃ is an important component in determining the reactivity of mineral dusts. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 242–249, 2006     

Effect of Hydrothermal Time,pH, and Alkali on Crystal Phase and Morphology of Manganese Oxides

γ‐MnOOH nanowires and Mn₃O₄ nanoparticles were prepared in the hydrothermal process. The effect of hydrothermal time, pH, and alkali on morphology and composition of manganese oxides was investigated. The results of XRD, TEM, and SEM showed that the γ‐MnOOH prepared in shorter hydrothermal time was a mixture of nanocubes and nanowires, while in longer hydrothermal time was pure nanowires. Interestingly, increasing the pH of the reaction system from 8 to 10, the mixture of γ‐MnOOH nanowires and Mn₃O₄ nanoparticles was obtained. Alkali types also were discussed in directing the reaction and crystallization of manganese oxides. The product was pure γ‐MnOOH when using NaOH in the system, but a mixture of Mn₃O₄ and γ‐MnOOH was obtained when using NH₃ · H₂O.