Facile synthesis of thermally stable mesoporous crystalline alumina by using a novel cation–anion double hydrolysis method

By using the double hydrolysis of Al³⁺ and AlO₂^- in the presence of Pluronic P123 as the structure directing agent, mesoporous crystalline alumina was easily synthesized, which exhibits high specific surface area, narrow pore size distribution, and excellent thermal stability.     

N2 adsorption curve of mesoporous SiO2: A neglected characterization technique

Mesoporous SiO₂ sieve and SiO₂ nanoparticles were synthesized by a traditional method in the presence and absence of tri-block copolymer surfactant P123 as structure directed agent respectively. The characterization results show that the mesoporous SiO₂ sieve has larger specific area (789 m²/g) than SiO₂ nanoparticles (373 m²/g), and there exists a substantial difference in the N₂ adsorption curves between the two samples. A speculative scheme shows that the formation of bottleneck during the N₂ adsorption process of mesoporous SiO₂ sieve should be responsible for the phenomenon.     

Controllable synthesis and magnetic properties of Fe3O4 and Fe3O4@SiO2 microspheres

We present a systematic study on the preparation, microstructure, and magnetic properties of Fe₃O₄ microspheres and Fe₃O₄@SiO₂ microspheres. Results showed that Fe₃O₄ microspheres’ diameter can be tuned by Fe³⁺ concentration, whereas their average grain size can be tuned by polyethylene glycol (PEG) 2000 dosage or PEG molecular weight. The magnetic saturation value of Fe₃O₄ microspheres was observed to be dependent on their average grain size, but not the sphere diameter. Fe₃O₄@SiO₂ microspheres with different magnetic saturation values were achieved by adjusting shell thickness. Furthermore, the synthesized Fe₃O₄ and Fe₃O₄@SiO₂ microspheres with high and controllable magnetic saturation value endow them with great application potentials.     

Morphological control on SBA-15 mesoporous silicas via a slow self-assembling rate

Pluronic 123-templated mesoporous SBA-15 silica rods with a length of ca. 3.0–4.0 μm were easily synthesized in a dilute silicate solution with a pH value of 2.0 at room temperature. Through a good control on the synthetic condition and the chemical components, a high homogeneity (>95%) of the hexagonal SBA-15 silica rods can be achieved. In addition, the effect of the synthetic conditions including acid source, weight ratio of the P123/sodium silicate, temperature, water content, pH value, and applying shearing flow were explored in detail to tailor the morphologies of the SBA-15 mesoporous silicas. In this paper, we also focused on the counterion effect on the synthesis of the SBA-15 mesoporous silicas. It was found that the SO₄ ²⁻ counterion from H₂SO₄ has higher affinity to induce the formation of P123 rod-like micelles than that of Cl⁻, NO₃ ⁻. Meanwhile, we postulated that the self-assembly pathway of the silica species and the neutral tri-block copolymer micelles in a dilute solution with a pH value of 2.0 would occur through an S⁰···I⁰ rather than the S⁰X^−…I⁺ one as previously discussed. We further employed the SAB-15 mesoporous silica rods as the templates to synthesize high-quality CMK-3 mesoporous carbon rods by using commercially available phenol–formaldehyde (PF) resin as the carbon source.     

Influence of dispersant on the morphology of silica-coated cobalt nanoparticles synthesized by a wet based method

Co/SiO₂ nanospheres with nearly perfect core–shell structure were prepared by an improved sol–gel method combined with hydrogen reduction. The products were characterized by X-ray diffraction spectra (XRD), transmission electron microscopy (TEM) and Fourier transform infrared (FT-IR) spectra. The results indicated that polyethylene glycol (PEG 8000) could act as a more efficient dispersive reagent than citric acid monohydrate (CAM). The average size of Co nanoparticles can be well controlled with optimum concentration of PEG 8000 and the average diameter of Co nanoparticles reaches about 30 nm with PEG 8000 concentration of 50 mg ml⁻¹.     

Synthesis of spheroidal ordered mesoporous carbon materials from silica/P123/butanol composites

Spheroidal ordered mesoporous carbon materials with diameter of 2–10 μm were synthesized by direct carbonization of silica/triblock copolymer P123/butanol composites using P123 and butanol as the structure-directing agents and carbon precursors. The morphologies, structures and pore characteristics of the carbon materials were investigated by scanning and transmission electron microscopes, X-ray diffraction, and nitrogen sorption. It was found that the material possesses a cubic ordered mesoporous structure with Ia3d symmetry. The butanol addition directly affects the carbon morphology and pore structure. When the mass ratio of butanol to P123 is 0.5:1, the product exhibits a perfectly spheroidal morphology with a specific surface area of 1236 m² g⁻¹ and a total pore volume of 1.26 cm³ g⁻¹. The formation mechanism of the spheroidal ordered mesoporous carbon materials is discussed briefly.     

Simple preparation of silica and alumina with a hierarchical pore system via the dual-templating method

Silica and alumina with macro-meso-type hierarchical pore systems are synthesized by dual templating using both surfactants and polystyrene (PS) spheres. After calcination, scanning electron microscope images show uniform macropores with a diameter of approximately 200 nm. This size coincides with that of the original PS spheres. The density of the macropores increases with the amount of added PS spheres in the precursor solutions. Transmission electron microscope images, small-angle x-ray scattering spectra and N₂ adsorption–desorption isotherms reveal the formation of ordered mesoporous structures in the macropore walls. Also, the existence of micropores (less than 2 nm in size) was confirmed from the large N₂ uptake at low relative pressures.     

Preparation and characterization of Al2O3-Ti3SiC2 composites and its functionally graded materials

Alumina/titanium silicon carbide (Al₂O₃-Ti₃SiC₂) composites and its functionally graded materials (FGMs) were fabricated by a powder metallurgy processes and their microstructure and properties were investigated, respectively. The experimental results showed that the Vickers hardness of composites decreased with increasing Ti₃SiC₂ content while the fracture toughness and strength exhibited the opposite trend. Minimum Vickers hardness (4 GPa), maximum strength (598 MPa) and maximum toughness (11.24 MPa m^1/2) were reached in the pure Ti₃SiC₂ material. Strength and hardness of FGMs were evaluated. Observation using an scanning electron microscope (SEM) indicated that the presence of Ti₃SiC₂ of FGMs inhibited the growth of alumina grains through a pinning mechanism. The study shows that the combination of the layered Ti₃SiC₂ structure and the fine alumina grains can result in a Al₂O₃-Ti₃SiC₂ composites possessing a high toughness and low Vickers hardness without a sacrifice in the strength.     

Simple preparation of silica and alumina with a hierarchical pore system via the dual-templating method

Abstract

Silica and alumina with macro-meso-type hierarchical pore systems are synthesized by dual templating using both surfactants and polystyrene (PS) spheres. After calcination, scanning electron microscope images show uniform macropores with a diameter of approximately 200 nm. This size coincides with that of the original PS spheres. The density of the macropores increases with the amount of added PS spheres in the precursor solutions. Transmission electron microscope images, small-angle x-ray scattering spectra and N₂ adsorption–desorption isotherms reveal the formation of ordered mesoporous structures in the macropore walls. Also, the existence of micropores (less than 2 nm in size) was confirmed from the large N₂ uptake at low relative pressures.     

A new synthetic procedure for ordered mesoporous γ-alumina using phthalic acid as an interfacial protector

Employing phthalic acid (PA) as an interfacial protector and P123 as a structure-directing agent, ordered mesoporous γ-alumina with 2D hexagonal symmetry was successfully synthesized through the sol-gel method. According to the results, the best molar ratio of PA/Al³⁺ to synthesize the ordered alumina is 0.25 and the phthalic acid serves as an interfacial protector to protect the aluminum ions at the organic-inorganic interface from being affected by chloride ions during the whole evaporation process. The resulting alumina possesses a surface area of 431.98 m²/g and a pore volume of 0.42 cm³/g. After the alumina converted into the γ-alumina phase, the surface area is still 226.37 m²/g and has a pore volume of 0.31 cm³/g.     

A facile synthesis strategy for structural property control of mesoporous alumina and its effect on catalysis for biodiesel production

A facile synthesis route for the production of mesoporous alumina (MA) with tuneable structural properties including BET surface area, pore volume and pore size was systematically investigated by tailoring the amount of template P123 used in the synthesis. The general synthesis strategy was based on a sol–gel process by hydrolysis of aluminium isopropoxide associated with nonionic block copolymer (P123) as the template in a water system. The results showed that the addition of P123 played a crucial role in the synthesis process, leading to very regular variations in the surface area (146.6–261.6 m²/g), pore volume (0.164–2.152 cm³/g) and pore size (3.5–29.9 nm). MA-supported K species (MA-K) were prepared using KNO₃ as the potassium precursor and adopted as the catalysts for biodiesel production. The introduction of K species to MA caused a reduction in the BET surface area and pore volume, but gave rise to a significant increase in pore size, especially when the K species was higher than 10%. K incorporation resulted in the formation of disordered, but significantly larger mesopores. In catalysis, by introducing 20% molar fraction of K species to MA, very high yield of biodiesel was achieved (92.2%) and further increased to 94.4% with 25% K. Based on the control of structural properties of MA, a series of MA-20K catalysts with the same K loading (20%) but different structural properties were prepared by varying P123 addition and were further tested in biodiesel synthesis. Higher biodiesel yields were obtained over the MAs with higher surface area, pore volume and bigger pore size, which were attributed to the reduced mass transfer limitation in catalysis.     

The production of grain oriented lanthanum titanate (La2Ti2O7) ceramics by uniaxial hot-forging process for improved fracture toughness

The layered-structural ceramics, such as lanthanum titanate (La₂Ti₂O₇), have been known for their good electrical and optical properties at high frequencies and temperatures. However, few studies have been conducted on the mechanical properties of these ceramics. The interest in ceramic hot-forging (HF) has been greatly increased recently due to the enhancement in fracture toughness via bridging effect of oriented grains. In this study, grain oriented lanthanum titanate was produced by the hot-forging process. The characterizations of the samples were achieved by density measurement, scanning electron microscopy (SEM), optical microscopy, X-ray diffraction (XRD), Vickers indentation and three-point bending test. According to X-ray diffraction patterns, the orientation factor (f) was found to be 0.73 for certain hot-forging conditions resulting an improved fracture toughness. The improved fracture toughness of La₂Ti₂O₇ (3.2 MPa m^1/2) reached to the value of monolithic alumina (Al₂O₃) between 3 and 4 MPa m^1/2.     

Fabrication of silica monolithic columns with ordered meso/macropore structure

Recently, much effort has been focused on the materials with ordered meso/macropores, because of their potential applications in catalysis, separations, coatings, microelectronics and electro-optics. In this paper, silica monoliths with well-defined columnar shape more than 1 cm in length are successfully fabricated by using the micelles of triblock copolymer F127 and colloidal crystals composed of polystyrene (PS) latex microspheres as mesopore and macropore template, respectively. The column templated by PS microspheres 870 nm in diameter and 0.5 g F127 (MCL-0.5-870) shows uniform ordered macropores, contact pores connecting macropores together, and assembled and inter-particle pores increasing the BET specific surface area and adsorption capability of the monolithic column. The backpressure curve and hydraulic permeability experiment exhibit its good penetrability and mechanical stability. These excellent characteristics, together with high BET specific surface area (387.4 m² g⁻¹) and porosity (80%), may endow its potential application for chromatography separation. In addition, the size of macropores and mesopores can be easily regulated by changing the diameter of PS spheres and F127 weight, respectively. This indicates that this method is a facile and universal protocol to fabricate the applied monolithic column with ordered meso/macropores.     

Microwave synthesis and electrochemical characterization of mesoporous carbon@Bi2O3 composites

An efficient and quick microwave method has been employed to prepare worm-like mesoporous carbon@Bi₂O₃ composites for the first time. As-prepared products have been characterized by X-ray diffraction, N₂ adsorption-desorption, scanning electron microscopy, transmission electron microscopy and inductive coupled plasma atomic emission spectroscopy. The electrochemical measurement shows the worm-like mesoporous carbon@Bi₂O₃ composites exhibits excellent capacitance performance and the maximum specific capacitance reaches 386 F g⁻¹, three times more than the pure worm-like mesoporous carbon.     

Modification and optimization of nano-crystalline Al2O3 combustion synthesis using Taguchi L16 array

Nanocrystalline Al₂O₃ powders have been synthesized by combustion method using 8 new fuels. The effectiveness of important factors on the production of nanopowders was investigated and optimized using Taguchi L₁₆ array design. The products were characterized by XRD, BET, TGA, EDX, FESEM, and TEM analyses. Results demonstrated that the alumina nanoparticles had crystallite sizes between 8.31 nm and 13.54 nm. The optimized sample had the specific surface area of 72 m²/g and crystallite size of 7.25 nm. The synthesis of γ-alumina was modified in order to achieve higher specific surface area (122.63 m²/g). A nano-network of alumina powders woven by alumina nano-fibers has been fabricated successfully by modified combustion synthesis. The length and diameter of fibers were about 160 nm and 10 nm respectively.     

Facile and controllable preparation of mesoporous TiO<Subscript>2</Subscript> using poly(ethylene glycol) as structure-directing agent and peroxotitanic acid as precursor

This work demonstrated that mesoporous TiO₂ (meso-TiO₂) with controllable mesoporous and crystalline structures can be facilely prepared by using poly (ethylene glycol) (PEG) as structure-directing (SD) agent and peroxotitanic acid (PTA) as precursor. Meso-TiO₂ with high specific surface area (157 m²?g^-1), pore volume (0.45 cm³?g^-1) and large mesopore size of 13.9 nm can be obtained after calcination at 450°C. Such meso-TiO₂ also shows relatively high thermal stability. BET surface area still reaches 114 m²?g^-1 after calcination at 550°C. In the synthesis and calcination process, PEG that plays multiple and important roles in delivering thermally stable and tunable mesoporous and crystalline structures shows to be a suitable low-cost SD agent for the controllable preparation of nanocrystalline meso-TiO₂. The photocatalytic activity tests show that both high surface area and bi-crystallinity of obtained meso-TiO₂ are important in enhancing the performance in photo-decomposing Rhodamine B in water.     

Highly-ordered mesoporous titania thin films prepared via surfactant assembly on conductive indium-tin-oxide/glass substrate and its optical properties

Highly ordered mesoporous titanium dioxide (titania, TiO₂) thin films on indium-tin-oxide (ITO) coated glass were prepared via a Pluronic (P123) block copolymer template and a hydrophilic TiO₂ buffer layer. The contraction of the 3D hexagonal array of P123 micelles upon calcination merges the titania domains on the TiO₂ buffer layer to form mesoporous films with a mesochannel diameter of approximately 10 nm and a pore-to-pore distance of 10 nm. The mesoporous titania films on TiO₂-buffered ITO/glass featured an inverse mesospace with a hexagonally-ordered structure, whereas the films formed without a TiO₂ buffer layer had a disordered microstructure with submicron cracks because of non-uniform water condensation on the hydrophobic ITO/glass surface. The density of the mesoporous film was 83% that of a bulk TiO₂ film. The optical band gap of the mesoporous titania thin film was approximately 3.4 eV, larger than that for nonporous anatase TiO₂ (~ 3.2 eV), suggesting that the nanoscopic grain size leads to an increase in the band gap due to weak quantum confinement effects. The ability to form highly-ordered mesoporous titania films on electrically conductive and transparent substrates offers the potential for facile fabrication of high surface area semiconductive films with small diffusion lengths for optoelectronics applications.     

The synthesis of large mesopores alumina by microemulsion templating,their characterization and properties as catalyst support

Large mesoporous aluminas have been prepared by the hydrolysis of aluminum tri-sec-butoxide in the presence of cetyltrimethylammonium bromide (CTAB) using oil-in-water microemulsion template. These resulting materials showed a disordered mesostructure with large mesopore frameworks. It is found to convert the intermediate phase (hydrated pseudoboehmite) into γ-Al₂O₃ at 268.7 °C. The large mesoporous alumina materials possess relative narrow mesoporous size distribution, high surface area (407.2 m²/g) and pore volumes (0.877 cm³/g). The prepared materials exhibited higher performance as catalyst support than that of the similar commercial γ-Al₂O₃ granules.     

Effects of Y2O3 addition on microwave dielectric characteristics of Al2O3 ceramics

Microwave dielectric characteristics of alumina ceramics with yttria addition were investigated. The sintering temperature was lowered, and the dielectric constant (ε_r) did not remarkably change by adding yttria. The microwave dielectric loss (tan δ) increased from 8.4 × 10^− 5 to 2.2 × 10^− 4, due to the presence of Al₅Y₃O₁₂ secondary phase. The grain size had significant effects on the dielectric loss, and there was an optimum grain size where the dielectric loss reached the minimum.     

Interaction mediated by size differences between Y2BaCuO5 and CeO2 particles in melt-textured YBCO superconductors

The Refining of Y₂BaCuO₅ (Y211) is crucial in the fabrication of YBa₂Cu₃O_x (Y123) bulk superconductors with a high critical current density (J_c) for power engineering applications.In this work, the influence of an addition of Y211 and CeO₂ of different sizes on the Y211 refinement and superconducting properties of melt-textured Y123 superconductors is investigated. Nano-size Y211 and nano-size CeO₂ were prepared by attrition-milling (250 rpm and 2 h). Using mixed powders consisting of 85 wt.% Y123, 15 wt.% Y211, and 1 wt.% CeO₂, Y123 quasi-single crystals were fabricated via a top seed melt-textured growth process. The interaction between Y211 and CeO₂ of different particle sizes was examined in terms of the size, uniformity and density of the Y211 particles that existed in the melt-textured samples. The reaction between the nano-size Y211 and the nano-size CeO₂ was more violent due to the more frequent collisions compared to the other reactions (micro-size Y211/nano-size CeO₂ or micro-size Y211/micro-size CeO₂), resulting in the most effective for refinement of Y211 particles and the best J_c value of 4.2 × 10⁴ (A/cm²) (at 77 K and a zero-field).