Morphological control of mesoporous alumina nanostructures via template-free solvothermal synthesis

Mesoporous alumina nanostructures with tunable morphologies have been synthesized using different solvents through the template-free solvothermal approach. Powder X-ray diffraction (XRD), transmission electron microscopy (TEM), selected-area electron diffraction (SAED), and nitrogen adsorption/desorption were used to characterize the samples. By manipulating the volume ratio and the composition of the reaction solvent, various morphologies of mesoporous alumina with crystalline-framework walls, i.e. nanotubes, nanofibers, nanorods, nanolaths, and nanosheets were synthesized. The specific surface area and the pore size correlated with the morphologies of γ-alumina nanocrystals. In comparison with conventional surfactant-templating methods, the new approach is simple and more suitable for industrial scale production.     

A facile method for the production of high-surface-area mesoporous silica gels from geothermal sludge

Mesoporous silica gels were successfully produced from geothermal sludge by alkali extraction followed by acidification. The silica in the geothermal sludge was dissolved by NaOH solution to produce a sodium silicate solution, which was then reacted with HCl or tartaric acid to produce silica gels. The effects of silica concentration and pH on the silica gel properties were investigated. In addition, an improved method was proposed by incorporating two-step aging. The first aging step, which was conducted at pH 10, was used to induce Ostwald ripening to increase the size of the primary particles, and the second step was used to strengthen the gel network. Decreasing the silica concentration by diluting the as-prepared sodium silicate solution tended to increase the surface area and pore volume of the prepared silica gels. The silica gels produced by tartaric acid possessed higher surface area and pore volume than those by HCl. The surface area and pore volume reached approximately 450 m² g⁻¹ and 0.8 cm³ g⁻¹, respectively. When the gelation pH was decreased to 6, the surface area exceeded 600 m² g⁻¹. The first aging process increased the size and uniformity of the primary particles, which in turn increased the surface area of the particles. The pore diameter for all cases was greater than 5 nm, indicating that the silica gels were mesoporous.     

Mechanochemical synthesis,structural, magnetic,optical and electrooptical properties of CuFeS2 nanoparticles

The rapid mechanochemical synthesis of nanocrystalline CuFeS₂ particles prepared by high-energy milling for 60?min in a planetary mill from copper, iron and sulphur elements is reported. The CuFeS₂ nanoparticles crystallize in tetragonal structure with mean crystallite size of about 38?±?1?nm determined by XRD analysis. HRTEM study also revealed the presence of nanocrystals with the size of 5–30?nm with the tendency to form agglomerates. The Raman spectrum confirms the chalcopyrite structure. Low temperature magnetic data for CuFeS₂ support the coexistence of antiferromagnetic and paramagnetic spin structure. Moreover, the hysteresis loops taken at temperatures from 5?K to 300?K revealed a presence of very small amount of ferromagnetic phase, which seems to be associated with the non-consumed elemental Fe in as-prepared nanoparticles. The optical band gap of CuFeS₂ nanoparticles has been detected to be 1.05?eV, larger than band gap of the bulk material. The wider gap possibly resulted from the nano-size effect. Photoresponses of CuFeS₂ nanoparticles were confirmed by I-V measurements under dark and light illumination. It was demonstrated that mechanochemical synthesis can be successfully employed in the one step preparation of nanocrystalline CuFeS₂ with good structural, magnetic, optical and electrooptical properties.     

A facile synthesis of monodisperse Au nanoparticles and their catalysis of CO oxidation

Monodisperse Au nanoparticles (NPs) have been synthesized at room temperature via a burst nucleation of Au upon injection of the reducing agent t-butylamine-borane complex into a 1, 2, 3, 4-tetrahydronaphthalene solution of HAuCl₄·3H₂O in the presence of oleylamine. The as-synthesized Au NPs show size-dependent surface plasmonic properties between 520 and 530 nm. They adopt an icosahedral shape and are polycrystalline with multiple-twinned structures. When deposited on a graphitized porous carbon support, the NPs are highly active for CO oxidation, showing 100% CO conversion at −45 °C. This article is published with open access at Springerlink.com     

Facile synthesis of layered sodium disilicates as efficient and recoverable nanocatalysts for biodiesel production from rapeseed oil

In this study, α, β and δ phases of layered sodium disilicates were synthesized and used as heterogeneous catalysts for transesterification of rapeseed oil with methanol to methyl esters (biodiesel). The catalysts were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) technique, Fourier transform infrared spectroscopy (FT-IR), N₂ adsorption-desorption, and thermogravimetric analysis (TGA-DTA). δ-Na₂Si₂O₅ showed better catalytic efficiency than the other two phases of sodium disilicate, and showed excellent activity at the optimized conditions. The transesterification conditions, such as the catalyst dosage, molar ratio of methanol to oil, reaction temperature and reaction time were investigated. The results revealed that with a catalyst loading of 4?wt%, methanol to oil ratio of 30:1, reaction temperature of 65?°C and reaction time of 3?h, conversion of biodiesel reached 97.8%.     

Direct template synthesis of mesoporous carbon and its application to supercapacitor electrodes

A direct templating method which is facile, inexpensive and suitable for the large scale production of mesoporous carbon is reported herein. A meso-structure surfactant/silicate template was made in a solution phase and resorcinol-formaldehyde as a carbon precursor was incorporated into the template solution. After aging, carbonization and hydrofluoric acid (HF) etching, mesoporous carbon was obtained. Using X-ray diffraction, scanning and transmission electron microscopy and nitrogen sorption, the synthesis mechanism of the mesoporous carbon was elucidated. According to the small angle X-ray scattering measurements, the surface became smoother after the removal of the silica, indicating that the silica was mostly located at the pore surface of the carbon. Also, the calculation of the pore volume demonstrated that the silica was transferred into the pores of the carbon without structural collapse during HF etching. When the prepared mesoporous carbon was applied to a supercapacitor electrode, the rectangular shape of the cyclic voltammogram was less collapsed, even at a high scan rate, which is indicative of its high rate capability. This was due to the low resistance of the electrolyte in the pores (3.8 Ω cm²), which was smaller than that of conventional activated carbon electrodes and even comparable to that of ordered mesoporous carbon electrodes. This improved performance was probably due to the well developed mesoporosity and high pore connectivity of the prepared mesoporous carbon.     

Effect of alumina doping on structural, electrical, and optical properties of sputtered ZnO thin films

A systematic study of the influence of alumina (Al₂O₃) doping on the optical, electrical, and structural characteristics of sputtered ZnO thin films is reported in this study. The ZnO thin films were prepared on 1737F Corning glass substrates by R.F. magnetron sputtering from a ZnO target mixed with Al₂O₃ of 0-4 wt.%. X-ray diffraction (XRD) analysis demonstrates that the ZnO thin films with Al₂O₃ of 0-4 wt.% have a highly (002) preferred orientation with only one intense diffraction peak with a full width at half maximum (FWHM) less than 0.5°. The electrical properties of the Al₂O₃-doped ZnO thin films appear to be strongly dependent on the Al₂O₃ concentration. The resistivity of the films decreases from 74 Ω·cm to 2.2 × 10^− 3 Ω·cm as the Al₂O₃ content increases from 0 to 4 wt.%. The optical transmittance of the Al₂O₃-doped ZnO thin films is studied as a function of wavelength in the range 200-800 nm. It exhibits high transparency in the visible-NIR wavelength region with some interference fringes and sharp ultraviolet absorption edges. The optical bandgap of the Al₂O₃-doped ZnO thin films show a short-wavelength shift with increasing of Al₂O₃ content.     

Effect of synthesis methods for mesoporous zirconia on its structural and textural properties

Zirconia was synthesized by sol–gel and post-hydrothermal treatment under autogenous pressure in order to study the effect of synthesis methods on its structural and textural properties. On the basis of thermal analysis, in situ X-ray diffraction and Raman spectroscopy techniques, the synthesis processes exhibit similar thermal behavior and zirconia phase transformation. The effect of in situ calcination temperature on the crystallization behavior, crystal phase transition, and crystallite size analysis was studied. The results obtained revealed that amorphous zirconia transformed into tetragonal phase above 400 °C and thermally stabilized up to 700 °C. A biphasic mixture of tetragonal and monoclinic zirconia was formed at 750 °C. Activation energy of sintering due to grain growth mechanism predicted that the zirconia phase transformation is due to the increase in the crystallite size of tetragonal phase above its critical size. The post-hydrothermal treatment resulted in the formation of high surface area mesoporous zirconia (213 m² g^?1). Upon increasing the calcination temperature, a pronounced decrease in the specific surface area of zirconia samples due to sintering process and phase transformation.     

A facile and novel way for the synthesis of nearly monodisperse silver nanoparticles

A facile and novel way was reported for the preparation of nearly monodisperse silver nanoparticles with controlled hydrophilic or hydrophobic surface, using trioctylphosphine as the surfactant and stabilizer. The synthesized nanoparticles were characterized by transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED) and UV-vis spectroscopy. The monodisperse silver nanoparticles showed a strong surface plasmon resonance band at 402 nm from the UV-vis spectrum.     

ZnO impregnated MgAl(O) catalyst with improved properties for biodiesel production: The influence of synthesis method on stability and reusability

ABSTRACT

A magnesium-aluminum layered double hydroxide was synthesized with co-precipitation method and zinc salt was impregnated on it. The final product was calcined and used as a catalyst in the transesterification reaction to produce biodiesel from waste cooking oil. Both MgAl hydrotalcite and Zn impregnated compound (Zn/MgAl(O)) were characterized using X-Ray Diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy (EDS) techniques. High surface area and nanometric pore size of Zn/MgAl(O) was determined using Bruneure-Emmett-Teller N₂ physisorption technique. Another fully co-precipitated ZnMgAl mixed oxide was synthesized by and compared with Zn impregnated product in the transesterification reaction. The reactions were performed at 65°C using 9:1 methanol to oil ratio for 3?h. The biodiesel yields were measured by gas chromatography (GC). Leaching amounts of surface active components of as-synthesized mixed metal oxides were determined by EDS and ICP analysis of used catalyst. Zn impregnated catalyst showed 78.45% conversion of the fatty acid to methyl esters and just 1.16% leaching of Zn was observed, that is much lower than the diminishing in the co-precipitated compound. Finally, the reaction and leaching proofs and the effect of synthesis method on the firmness of catalyst were discussed.     

Recent progress in molten salt synthesis of low-dimensional perovskite oxide nanostructures,structural characterization,properties, and functional applications: A review

Molten salt synthesis (MSS) method has advantages of the simplicity in the process equipment, versatile and large-scale synthesis, and friendly environment, which provides an excellent approach to synthesize high pure oxide powders with controllable compositions and morphologies. Among these oxides, perovskite oxides with a composition of ABO3 exhibit a broad spectrum of physical properties and functions (e.g. ferroelectric, piezoelectric, magnetic, photovoltaic and photocatalytic properties). The downscaling of the spatial geometry of perovskite oxides into nanometers result in novel properties that are different from the bulk and film counterparts. Recent interest in nanoscience and nanotechnology has led to great efforts focusing on the synthesis of low-dimensional perovskite oxide nanostructures (PONs) to better understand their novel physical properties at nanoscale. Therefore, the low-dimensional PONs such as perovskite nanoparticles, nanowires, nanorods, nanotubes, nanofibers, nanobelts, and two dimensional oxide nanostructures, play an important role in developing the next generation of oxide electronics. In the past few years, much effort has been made on the synthesis of PONs by MSS method and their structural characterizations. The functional applications of PONs are also explored in the fields of storage memory, energy harvesting, and solar energy conversion. This review summarizes the recent progress in the synthesis of low-dimensional PONs by MSS method and its modified ways. Their structural characterization and physical properties are also scrutinized. The potential applications of low-dimensional PONs in different fields such as data memory and storage, energy harvesting, solar energy conversion, are highlighted. Perspectives concerning the future research trends and challenges of low-dimensional PONs are also outlined.     

Novel low temperature synthesis of ZnO nanostructures and its efficient field emission property

We have developed a novel, simple and cost effective wet chemical synthetic route for the production of ZnO nanoneedles and nanoflowers at low temperature. The synthesis process does not require any surfactant, template or pre-seeding. The synthesized ZnO nanoneedles have very sharp tips with their lengths in the range 2-3 μm, while for the case of nanoflowers, the nanoneedles were bunched together. X-ray diffraction study and X-ray photoelectron spectroscopic studies confirmed the formation of pure ZnO phase. Studies on the electron field emission property of the grown nanostructures showed that they are very efficient field emitter. The turn-on fields and the threshold fields are 3.6 V/μm, 4.4 V/μm and 5.4 V/μm, 6.8 V/μm for the ZnO nanoneedles and ZnO nanoflowers, respectively. The enhanced field emission property was attributed to the presence of sharp tips of the nanostructures.     

Investigation on one-pot hydrothermal synthesis,structural and optical properties of ZnS quantum dots

The advantage of hydrothermal synthesis of semiconductor quantum dots (QDs) over the control of particles size, morphology and stability is reported here. In a typical synthesis procedure, the zinc and sulfur precursor molar ratio of 1:3 was used in an aqueous solution at 150 °C. The cubic phase of ZnS with average particles size of 5 nm was confirmed and estimated from the X-ray diffraction (XRD) analysis. The composition and purity of the sample were analyzed from (energy dispersive-ray analysis) EDAX and (X-ray photoelectron spectroscopy analysis) XPS spectra. The absorption spectrum shows the large shift in the absorption band over 90 nm due to the quantum confinement of carriers. The emission spectrum of quantum dots carry more evidence on the presence of shallow trap, deep trap in the band gap of the material responsible for weak emission in the spectral region of 450–500 nm. High resolution transmission electron microscope and scanning electron microscope studies reveal the structural and morphological features of ZnS with slightly distorted spherical morphology. We found that the coordinating ability of solvent strongly influences the reaction process and morphology of the products.     

Comparative study on the structural and catalytic properties of mesoporous hexagonal silica anchored with H3PW12O40: Green synthesis of benzoic acid from benzaldehyde

Mesoporous silica anchored with 25 wt.% 12-tungstophosphoric acid (H₃PW₁₂O₄₀, HPW) were comparatively characterized on their structures and catalytic activities for benzaldehyde oxidation with H₂O₂. The results revealed that the mesoporous materials retained the typical hexagonal mesopores for the supports of HPW. It was found that HPW exhibited higher dispersion within MCM-41 than those within SBA-15 and other mesoporous molecular sieves. Moreover, the as-prepared materials were found to be the efficient catalysts for the green synthesis of benzoic acid. In particular, HPW/MCM-41 exhibited the best catalytic properties due to its suitable textural and structural characteristics.     

A numerical study of the heterogeneous porosity effect on self-propagating high-temperature synthesis (SHS)

Self-propagating high-temperature synthesis (SHS), or the so-called micropyretic/combustion synthesis, is a technique whereby a material is synthesized by the propagation of a combustion front across a powder. Heterogeneous distributions of porosities are common during self-propagating high-temperature synthesis when powders are pressed and the conventional modeling treatments thus far have only considered uniform systems. Heterogeneities in the porosity are thought to result in local variations of such thermophysical/chemical parameters for the reactants as density and thermal conductivity further changing the combustion temperature, the propagation velocity, and the propagation pattern of a combustion front. This study investigates the impact of porosity variations during self-propagating high-temperature synthesis with Ti + 2B. In addition, the simulations for the propagation of combustion fronts across a non-uniform compact where the porosity is monotonically decreased or increased along the specimens due to die wall friction are also carried out.     

Effects of pH on morphosynthesis and photocatalytic activity of calcium titanium oxides via a facile aqueous strategy

By controlling pH values, calcium titanium oxides with various morphologies had been synthesized via a simple hydrothermal route. No surfactants or templates were involved in the shaping process. The results found that pH values had a crucial effect on the crystal phase and shape evolution of the samples. With increasing pH values, the obtained sample changed from one-dimension (1D) CaTi₂O₅ rod or shuttle-like shape to two-dimension (2D) CaTi₂O₄(OH)₂ nanosheets, and then to three-dimension (3D) CaTiO₃ aggregated prisms, butterfly-like dendrites and cross cubic shapes. The formation mechanism was proposed for the evolution of phase and morphology. 3D CaTiO₃ butterfly-like sample showed good photocatalytic activity due to unique morphology, enhanced light harvesting and large surface area.     

Combustion synthesis of Sr0.5Ba0.5Nb2O6 and effect of fuel on its microstructure and dielectric properties

Nano-sized Sr_0.5Ba_0.5Nb₂O₆ (SBN50) powder has been synthesized, at very short reaction time, for the first time by a novel combustion method. Ba(NO₃)₂ and Sr(NO₃)₂ were used as source of Sr and Ba, respectively, while Nb-oxalate was used as the source of niobium. Urea, hexamethyltetramine (HMT) and glycine were used as fuel. The crystallite sizes in the powder ranged between 14-125 nm. X-ray diffraction analysis showed complete SBN50 phase formation at 700 °C, when urea/HMT was used as fuel, and at 800 °C when glycine was used as fuel. Ferroelectric-paraelectric phase transition temperature (T_c) close to 40 °C was observed when urea and HMT were used and the T_c was −49 °C when glycine was used. When urea was used as fuel highest dielectric constant was observed for the pellets sintered at 1250 °C for 4 h. Low dielectric loss was observed when HMT was used as fuel. Larger grain sizes in the sintered pellets were observed when glycine was used as fuel.     

玄武岩纤维耐碱性及对混凝土力学性能的影响

为研究玄武岩纤维的耐碱性能及其对混凝土力学性能的影响规律,试验将玄武岩纤维分别置于不同碱浓度、不同温度的溶液中浸泡 1天、3天和5天后,测量其质量损失率;并在偏光显微镜下观察腐蚀后的表面形貌;同时研究了3种不同玄武岩纤维掺量的混凝土强度性能,采用SEM观察混凝土中纤维的腐蚀情况。结果表明,随着碱溶液浓度和浸泡温度的提高,纤维的质量损失率增加,表面剥落严重。玄武岩纤维混凝土与空白样相比7天的力学性能变化不大,而养护28天的抗压、抗折强度则随纤维掺量的增加有明显的下降,电镜照片显示混凝土中纤维表面被腐蚀,混凝土强度损失可能与玄武岩纤维耐碱性能不强有关。      

The synthesis of graphene nanoribbon and its reinforcing effect on poly (vinyl alcohol)

The graphene nanoribbon was prepared from the carbon nanotubes using the chemical approach, and was used for preparing the poly (vinyl alcohol) nanocomposites. It was discovered that the prepared graphene nanoribbon contained a lot of oxygen groups. Due to the presence of these oxygen groups, the nanoribbon could homogeneously disperse in both water and poly (vinly alcohol) matrix. It was also found that there were strong interactions between the graphene nanoribbon and the poly (vinyl alcohol) through hydrogen bonding. The interactions gave rise to the thermal stability of the host polymer. Furthermore, the presence of the nanofiller also resulted in a significant improvement of the mechanical performance of the prepared nanocomposites. The tensile strength and the Young’s modulus of the nanocomposite loaded with 2.0 wt% graphene nanoribbon increased by 85.7% and 65.2% respectively. The overall results indicate that the graphene nanoribbon is suitable for preparing high-performance polymer composites.     

偏苯三酸酐聚酯多元醇的合成及其在PU硬泡中的应用研究

以偏苯三酸酐、乙二醇或1,3-丁二醇为原料,单丁基氧化锡为催化剂,成功合成出多官能高羟值的偏苯三酸酐-乙二醇聚酯多元醇(TEPES)、偏苯三酸酐-1,3-丁二醇聚酯多元醇(TBPES)。结果显示,TE-PES的羟值、数均官能度(fn)及重均官能度(fw)分别为400.0mg KOH/g、6.55、7.31,TBPES的羟值、fn及fw分别为357.2mg KOH/g、5.87、6.49,且TB-PES的分子量分布较TEPES窄。1 H NMR谱与TGA分析表明,在反应过程中二元醇与偏苯三酸酐之间不仅存在单羟基的酯化反应,也存在双羟基的酯化反应;TBPES低温热稳定性比TEPES好,而其高温热稳定性不如后者。以聚醚多元醇GR-835G、TEPES、TB-PES、多亚甲基多苯基多异氰酸酯PM-200为主要原料,制备出多种不同复配多元醇体系的60kg/m3表观密度的PU硬泡。相比单一的GR-835G体系,TEPES与GR-835G的复配体系对PU硬泡压缩模量的改善有利,且其改善效果要好于TBPES与GR-835G的复配体系。同时,TEPES的掺入会损耗一定的压缩强度,而TBPES的掺入能使压缩性能整体都有提高。