In situ synthesis of porous ceramics with a framework structure of aluminium borate whisker

New porous ceramics with a framework structure of aluminium borate (9Al2O3 · 2B2O3) whiskers, in which the whiskers are distributed uniformly and randomly, can be synthesized in situ by firing of a green powder compact of a mixture of aluminium hydroxide, boric acid and an additive of nickel oxide above 1100°C. During firing, the whiskers of aluminium borate grow in situ in the compact, and are bonded together by sintering. The porous aluminium borate consists solely of whiskers, has a porosity of 85%–50%, which corresponds to a volume fraction of whiskers of 15%–50%, and a flexural strength of 2.2–56.1 MPa. Because the whiskers are strongly bonded to other whisker(s), the problem of whiskers scattering, that can be an inhalation hazard, is solved. The aluminium alloy matrix composite using this porous aluminium borate as reinforcement was fabricated by the squeeze-casting method. The tensile strength of the composite material with a whisker volume fraction of 20% can be improved by up to about 90% compared with the unreinforced matrix alloy at 350°C. © 1998 Chapman & Hall     

Amine-assisted synthesis of FeS@N-C porous nanowires for highly reversible lithium storage

Iron sulfide is an attractive anode material for lithium-ion batteries (LIBs) due to its high specific capacity, environmental benignity, and abundant resources. However, its application is hindered by poor cyclability and rate performance, caused by a large volume variation and low conductivity. Herein, iron sulfide porous nanowires confined in an N-doped carbon matrix (FeS@N-C nanowires) are fabricated through a simple amine-assisted solvothermal reaction and subsequent calcination strategy. The as-obtained FeS@N-C nanowires, as an LIB anode, exhibit ultrahigh reversible capacity, superior rate capability, and long-term cycling performance. In particular, a high specific capacity of 1,061 mAh·g^?1 can be achieved at 1 A·g^?1 after 500 cycles. Most impressively, it exhibits a high specific capacity of 433 mAh·g^?1 even at 5 A·g^?1. The superior electrochemical performance is ascribed to the synergistic effect of the porous nanowire structure and the conductive N-doped carbon matrix. These results demonstrate that the synergistic strategy of combining porous nanowires with an N-doped carbon matrix holds great potential for energy storage.

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Synthesis of continuous mesoporous Ga-doped titania films with anatase crystallized framework

Here we report synthesis of ordered mesoporous titania films with various amounts of Ga content. The influence of Ga contents on mesostructural ordering, surface morphology, thermal stability, and anatase crystallinity is carefully investigated, by using grazing incidence small angle X-ray scattering (GISAXS), transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM), and Raman spectroscopy. The presence of highly dispersed Ga contents in the titania frameworks can promote the thermal stability of mesoporous titania structures, resulting that the anatase crystallization successfully proceeds without collapse of mesostructures.     

Template-free synthesis of titania architectures with controlled morphology evolution

Template-free synthesis of TiO₂ architectures with controlled morphology evolution has been developed through solvothermal reaction in 1,4-dioxane. By simply varying the molar ratio of the concentrated HCl over Titanium isopropoxide (TTIP) from 0 to 5.0, series of morphologies including nanoparticle-built microspheres, nanoparticle-built microspheres decorated with nanorods, nanorod cauliflowers, and nanorod dendrites have been obtained. The influence of several key factors on the morphology control of TiO₂ has been systematically investigated. These parameters include the mass (molar) ratio of HCl/TTIP, solvothermal reaction temperature and time, acid species (concentrated nitric acid), and solvent type (tetrahydrofuran and 1,3-dioxane). The mechanism for the formation of the TiO₂ architectures with controlled morphology evolution has been discussed. The application of the TiO₂ architectures as water splitting photocatalyst and lithium–ion battery anode has been demonstrated. And the corresponding structure–property correlation has been discussed.     

Sol-gel synthesis of titania hollow spheres

TiO₂ hollow spheres are prepared by a convenient sol-gel method at room temperature. The products were characterized by XRD, FESEM, TEM and FT-IR. It was found that these spheres are hollow inside with outer diameters of 200-500 nm. The average mesoporous diameter is about 9.8 nm. And the BET surface area and specific pore volume are about 161.9 m²/g and 0.441 cm³/g, respectively.     

Formation and properties of porous silicon/titania nanostructures

Porous silicon/titania structures have been prepared for the first time by a sol-gel process in which a porous silicon layer was produced on single-crystal p-type silicon wafers and the titania was obtained from Ti-containing sol. The formation of TiO₂, predominantly in the form of anatase, on the porous silicon surface was demonstrated by X-ray diffraction and energy dispersive X-ray analysis. The porous layers were found to contain carbon in addition to the host elements (Si, Ti, and O). Increasing the pore volume through the thermal oxidation of the porous silicon and dissolution of the oxide layer had little effect on the final Ti content, whereas the average pore diameter increased twofold, and the photoluminescence intensity in the porous silicon increased by 20 times.     

Facile synthesis of the porous MnMo6S8 for highly stable pseudocapacitor

Transition metal sulfides are the prominent and leading materials for high-performance energy storage applications. Manganese molybdenum sulfide (MMS) is synthesized using facile hydrothermal method. The electrochemical active sites of the electrode material were enhanced by making the bi-metal sulfides with nanoporous diffusion channels in their crystal structure. The crystalline structure and morphology of the material were studied using X-ray diffraction pattern and high resolution-scanning electron microscope image, respectively. The functional groups present in the material were characterized using Fourier transform infrared spectrometer. MMS-coated nickel foam shows an excellent cycle stability. In 2 M KOH electrolyte, its specific capacity raised to 160% after 10,000 galvanostatic charge discharge (GCD) cycles at the current density of 10 A g^??1 and exhibited a higher specific capacity of 101.3 C g^??1 at 1 A g^??1. After 12,000 GCD cycles, the as-fabricated MMS//MMS symmetric device offers an elevated specific capacity of 228% from its initial value at the current density of 5 A g^??1.

     

Combustion synthesis of highly porous ceramics: The TiC-Al2O3 system

To make use of the porous nature of the SHS reaction products a novel investigation was made to manufacture the highly porous ceramics with SHS method by adding certain amounts of volatile agents to the green compacts. The interconnected open porosity of the obtained highly porous ceramics can be as high as 83% and the interconnected network open pore microstructure was developed in the obtained highly porous ceramics. Large amounts of micropores were found present in the obtained highly porous ceramics, which is a special and important advantage of manufacturing porous ceramics with SHS method. Also this particular combustion process was studied in detail and it was found that the propagation rates are increased considerably due to the unique green compact structure left by the volatile agents.     

Biogenic synthesis and thermo‐magnetic study of highly porous carbon nanotubes

Nanomaterials synthesis using natural sources is the technology to up come with advanced materials through extracts of plant, microorganisms, poultry waste etc. In this study, the authors report the synthesis of porous carbon nanotubes using high‐temperature decomposition technique facilitated by cobalt salt using chicken fats, a poultry waste as a precursor. Since chicken fats contain fatty acids which can decompose into short hydrocarbon chains and cobalt can act as the catalyst. The formation of carbon nanotubes was confirmed by Raman spectra, peaks at 1580 and 1350.46 cm⁻¹ confirmed the graphite mode G‐band and structural imperfections defect mode D‐band, respectively. Transmission electron microscopy showed the formation of tube‐like structures. Nitrogen adsorption–desorption studies showed the high‐surface area of 418.1 m² g⁻¹ with an estimated pore diameter of 8.1 nm. Thermogravimetry analysis–derivative thermogravimetric analysis–differential thermal analysis showed the instant weight loss at 517°C attributed to the rapid combustion of nanotubes. A vibrating‐sample magnetometer showed the paramagnetic nature of the so‐formed carbon nanotubes formed.Inspec keywords: transmission electron microscopy, infrared spectra, nanomagnetics, pyrolysis, decomposition, adsorption, desorption, carbon nanotubes, differential thermal analysis, thermal analysis, nanofabrication, Raman spectra, X‐ray diffraction, scanning electron microscopy, paramagnetic materialsOther keywords: biogenic synthesis, highly porous carbon nanotubes, microorganisms, high‐temperature decomposition technique, cobalt salt, chicken fats, fatty acids, short hydrocarbon chains, Raman spectra, graphite mode G‐band, structural imperfections defect mode D‐band, transmission electron microscopy, paramagnetic nature, thermo‐magnetic properties, poultry waste, nitrogen adsorption‐desorption studies, thermogravimetry analysis, differential thermal analysis, carbon nanotubes, temperature 517.0 degC, C     

Synthesis of porous micro-sized titania cages and their photocatalytic property

Micro-sized TiO₂ cage consisted of anatase nanoparticles on the edges of each cube, was synthesized using TTIP as the reagent and NaF submicrometer sized cubes as the template. When a salt of cube was adopted as the template, the reactants prefer to grow on the active sites, edges and corners of the cube, after removing the NaF template, the skeleton of the cube remain as the cage-shaped materials. The hierarchical structures with nano-sized anatase particles and micro scaled cage architecture markedly enlarge the surface area and enhance the light harvesting by light scattering of TiO₂ frame, resulting in great photo-catalytic performance, which leads to the photo-degradation of methylene blue by 40% higher than that was achieved by crushed nanoparticles.     

Formation mechanism of biomedical apatite coatings on porous titania layer

A titania containing calcium and phosphate with rough and porous structure was prepared by microarc oxidation. The in vitro bioactivity was examined by immersing the samples into the simulated body fluid (SBF). And the mechanism was also discussed. The results show that only 3 days of immersion in SBF, apatite was formed on the surface, and after 6 days, nearly all the surface covered by apatite. This indicates that the layer can induce the formation of apatite in simulated body fluid. It is analyzed that the key factors of the apatite formation are the hydrolysis of the CaTiO₃ and special structure.     

Processing and properties of porous titanium with high porosity coated by bioactive titania nanotubes

A porous titanium scaffold with a porosity of 70% and a pore size of about 200–300 μm was fabricated using the space-holder sintering process. Furthermore, the bioactive TiO₂ nanotubes with a tube size of approximately 100 nm were prepared successfully on the surface of the porous titanium by anodization and heat-treatment. The bioactivity of the scaffold was evaluated by immersing the samples into the simulated body fluid for 7 days. Results show that the porous titanium scaffold coated with anatase nanotubes has the superior ability of hydroxyapatite formation. Meanwhile, the scaffold has a high compressive strength of 36.8 MPa, which can be used as a cancellous bone substitute.     

One-pot pyrolysis synthesis of highly active Ru/RuOx nanoclusters for water splitting

Using simple methods to obtain efficient catalysts has been a long-standing goal for researchers.In this work,the employment of a one-pot pyrolysis reaction to achieve molecular confinement,has led to the preparation of ruthenium(Ru)-based nanoclusters in a carbon matrix.A unique feature of the synthetic approach employed is that solvent and substrates were calcined together.As solvent evaporates,during calcination,the substrates form a dense solid which has the effect of limiting the aggregation of Ru centers during the carbonization process.The catalyst prepared in this simple manner showed an impressively high activity with respect to the hydrogen/oxygen evolution reaction(HER/OER).The Ru nanoclusters(Ru NCs),as the hydrogen evolution reaction(HER)catalysts,require ultralow overpotentials of 5 mV and 5.1 mV at-10 mA·cm^-2 in 1.0 M KOH,and 0.5 M H₂SO₄,respectively.Furthermore,the catalyst prepared by the one-pot method has higher crystallinity,a higher Ru content and an ultrafine cluster size,which contributes to its exceptional electrochemical performance.Meanwhile,the RuO_x nanoclusters(RuO_x NCs),obtained by oxidizing the aforementioned Ru NCs,exhibited good oxygen evolution reaction(OER)performance with an overpotential of 266 mV at 10 mA·cm^-2.When applied to overall water splitting,Ru/RuO_x nanoclusters as the cathode and anode catalysts can reach 10 mA·cm^-2 at cell voltages of only 1.49 V in 1 M KOH.     

Evaluating the potential of a new titania precursor for the synthesis of mesoporous Fe-doped titania with enhanced photocatalytic activity

Mesoporous Fe (III) doped TiO₂ nanoparticles with an anatase phase were prepared by using a stable precursor potassium hexafluorotitanate as Ti source for the first time and its physical as well as photocatalytic properties were compared with that of Fe doped titania prepared from the most common Ti source titanium isopropoxide. FeSO₄·7H₂O and Fe (NO)₃·9H₂O were used for doping titania with Fe (III). Physicochemical properties of the samples were characterized by XRD, XPS, FTIR, Raman spectroscopy, N₂ adsorption–desorption isotherms, UV–vis diffuse reflectance spectroscopy. EDX confirms the presence of Fe. DRS and TEM reveals that doping has taken place. It was found that Fe-doped nanostructured titania prepared from potassium hexafluorotitanate was much more effective in the photocatalytic decomposition of bromocresol green than undoped nanostructured titania as well as commercial titania.     

One-step synthesis of N,P co-doped porous carbon electrocatalyst for highly efficient nitrogen fixation

Heteroatom-doped porous carbon has attracted many researchers'interests owing to their hierarchical porous and more active sites for nitrogen reduction reaction...     

Tunable synthesis of mesoporous titania with different morphologies for dye-sensitized solar cells

Different TiO₂ mesoporous structures, including core-shell spheres (CCSs) and micro-tubes (MTs), are synthesized through adjusting the pH of the solution using TiOSO₄ as titanium source in a hydrothermal route. TiO₂ CSSs with an average diameter of 1.3–3.5 μm exhibit excellent light scattering property and high specific surface area (177.63 m² g^?1). TiO₂ MTs show ultrahigh specific surface area of 276.03 m² g^?1. Dye-sensitized solar cell is fabricated using TiO₂ CSSs as the light scattering layer and TiO₂ nanoparticles (NPs) layer as the bottom layer. The efficiency of Cell-NPs + CSSs is up to 9.24% due to the good light scattering effect and excellent dye loading capacity. Furthermore, TiO₂ MTs are introduced to form the NPs/MTs bottom layer. The Cell-NPs/MTs + CSSs achieves an outstanding efficiency of 9.60% due to the further optimized electron transport path.     

超临界水热合成法制备TiO_2纳米粉体

采用超临界水热合成法制备TiO_2纳米粉体,研究反应条件包括温度、压力、反应时间对纳米粉体颗粒的粒径大小、形貌及结晶度的影响。结果表明,随着温度从亚临界升高到超临界,TiO_2颗粒粒径急剧减小,且结晶度增大,最终合成10 nm左右结晶度良好的椭球形颗粒。颗粒在26~30 MPa的压力范围内,结晶度随着反应压力的增大而增大,但粉体粒径大小差别不大。在1 min的反应时间内即检测出了TiO_2物相,而在5 min后生成了结晶良好的椭球形晶体,随着反应时间的增加,棒状的颗粒逐渐增多,这是由于发生了溶解-结晶机理。     

A flexible interpenetrating coordination framework with a bimodal porous functionality

Introducing a functional part into open-framework materials that tunes the pore size/shape and overall porous activity will open new routes in framework engineering and in the fabrication of new materials. We have designed and synthesized a bimodal microporous twofold interpenetrating network {[Ni(bpe)2(N(CN)2)](N(CN)2)(5H2O)}n (1), with two types of channel for anionic N(CN)2- (dicyanamide) and neutral water molecules, respectively. The dehydrated framework provides a dual function of specific anion exchange of free N(CN)2- for the smaller N3- anions and selective gas sorption. The N3-exchanged framework leads to a dislocation of the mutual positions of the two interpenetrating frameworks, resulting in an increase in the effective pore size in one of the counterparts of the channels and a higher accommodation of adsorbate than in the as-synthesized framework (1), showing the first case of controlled sorption properties in flexible porous frameworks.