Controlled synthesis of monodisperse nanocrystals by a two-phase approach without the separation of nucleation and growth processes

The synthesis of monodisperse nanocrystals is an important topic in the field of nanomaterials not only for practical applications, but also for scientific interest in fundamental research. In this feature article, we mainly focus on synthesis of monodisperse nanocrystals by a two-phase approach without the separation of nucleation and growth processes, and report some progress made recently in the observation and understanding of nucleation and growth of semiconductor nanocrystals. Firstly, a novel two-phase approach to monodisperse nanocrystals, which is different from the well-established synthesis models, is discussed. We demonstrate that the two-phase approach has a quite lengthy nucleation process, and can be applied to the synthesis of many kinds of binary monodisperse nanocrystals.

Sol-gel derived Y2O3 as an efficient bluish-white phosphor without metal activator ions

In this paper, Y2O3 powder phosphors without metal activators were successfully prepared by the sol-gel method. The obtained sample shows an intense bluish-white emission (ranging from 350 to 600 nm, centered at 416 nm) under a wide range of UV light excitation (235-400 nm). The chromaticity coordinates of the sample are x = 0.159, y = 0.097, and the quantum yield is as high as 64.6%, which is a high value among the phosphor family without metal activators. The luminescent mechanisms have been ascribed to the carbon impurities in the Y2O3 host.

High-pressure sintering the novel light (W0.25Al0.75)C hard material without binder phase

A novel hard material of (W0.25Al75)C has been successfully prepared by the high-pressure sintering process without the addition of any binder phase. The high-pressure is a suitable and powerful technique for sintering the binderless hard material, the relative density of the hard material can reach 99.6% under high-pressure sintering. The density of the novel light hard material is only 6.2371 g cm(-3), which is much lighter than the normal hard material. The hardness of the light hard material can reach 18.89 GPa even the aluminum content get the astonished 75%.

Native growth of vertically pattened ZnO nanowire arrays under mild conditions without templates or catalysts

Based on the implications of a pellet experiment,we have designed and implemented a low temperature(≤90℃) approach to generate native patterned,vertically aligned ZnO nanoarrys without any templates or catalysts.This simple,economic and spontaneous patterning process offers a promising avenue for overcoming several inherent limitations of the artificial manners[1].While the purity,orientation and electrical properties of the as prepared materials allow them to be applied in various fields.

Selective synthesis of mesoporous and nanorod CeVO4 without template

A simple and efficient method has been established for the selective synthesis of mesoporous and nanorod CeVO4 with different precursors by sonochemical method. CeVO4 nanorod can be simply synthesized by ultrasound irradiation of Ce(NO3)(3) and NH4VO3 in aqueous solution without any surfactant or template. While mesoporous CeVO4 with high specific surface area can be prepared with Ce(NO3)(3), V2O5 and NaOH in the same way. Mesoporous CeVO4 has a specific surface area of 122 m(2) g(-1) and an average pore size of 5.2 nm; CeVO4 nanorods have a diameter of about 5 nm, and a length of 100-150 nm. The ultrasound irradiation and ammonia in the reactive solution are two key factors in the formation of such rod-like products. X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), thermogravimetric (TG) and differential thermal analyses (DTA), UV/vis absorption spectroscopy and Brunauer-Emmett-Teller (BET) were applied for characterization of the as-prepared products.

High-pressure sintering study of a novel hard material (W0.5Al0.5)C-0.5 without binder metal

A novel hard material of (W0.5Al0.5)C-0.5 has been successfully sintered under high-pressure (4.5 GPa). The influence of sintering time and temperature on the microstructure, Vickers microhardness and density of the as-prepared specimens are well described. Interestingly, sintering temperature has an amazing influence on the hardness, density and microstructure of the specimen while the sintering time does not. It is found that the most suitable sintering condition from our work is 1600 degrees C and 10 min under pressure of 4.5 GPa. The hardness and relative density of the as-prepared sample can reach 2340 kg mm(-2) and 98.62%, respectively. The cell parameters of the sintered specimen is found to be little smaller than that of the powder, which we propose is related to the high pressure.

Grain boundary conductivity of high purity neodymium-doped ceria nanosystem with and without the doping of molybdenum oxide

Solid solutions of Ce1-xNdxO2-x/2 (0.05 <= x <= 0.2) and (Ce1-xNdx)(0.95)MO0.05O2-delta (0.05 <= x <= 0.2) have been synthesized by a modified sol-gel method. Both materials have very low content of SiO2 (similar to 27 ppm). Their structures and ionic conductivities were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM) and electrochemical impedance spectroscopy (M). The XRD patterns indicate that these materials are single phases with a cubic fluorite structure. The powders calcined at 300 degrees C with a crystal size of 5.7 nm have good sinterability, and the relative density could reach above 96% after being sintered at 1450 degrees C. With the addition Of MoO3, the sintering temperature could be decreased to 1250 degrees C. Impedance spectroscopy measurement in the temperature range of 250-800 degrees C indicates that a sharp increase of conductivity is observed when a small amount of Nd2O3 is added into ceria, of which Ce0.85Nd0.15O1.925 (15NDC) shows the highest conductivity. With the addition of a small amount Of MoO3, the grain boundary conductivity of 15NDC at 600 degrees C increases from 2.56 S m(-1) to 5.62 S m(-1).

Electropolyrnerization of polypyrrole on PFIL-PSS-modified electrodes without added support electrolytes

A novel polyelectrolyte-functionalized ionic liquid (PFIL)/poly(4-styrene sulfonate sodium) (PSS) modified electrode composed of the coaxial and coplanar working, reference and counter electrodes, was used to electropolymerize the polypyrrole. The PFIL/PSS was modified on the integrated electrode (IE) and connected by the working, reference and counter electrodes, resulting in an available charge transfer and lower Ohmic potential drop between the working and counter electrodes. Then polypyrrole (PPy) film was successfully prepared electrochemically without any participation of supporting electrolytes, only in a pyrrole monomer solution. The resulting PPy film in PFIL/PSS matrix exhibited a preferable electroactivity. Subsequently, influence of the modifications on the formation of PPy was further discussed. The results indicated that the synergetic cooperation of PFIL and PSS components accomplished such a successful electropolymerization of PPy.

Oxygen permeating properties of the mixed conducting membranes without cobalt

A new series of mixed conducting oxides, Sr10-n/2BinFe20Om (n = 4, 6, 8, 10), were synthesized by a solid state reaction method, and they have high oxygen permeability. The oxygen permeation rate at 1150 K is 0.41 ml(STD)/ cm(2).min for n = 6 and 0.90 ml(STD)/cm(2).min for n = 10, which is two times higher than that for Sr1-xBixFeO3 (x = 0.5). For the Sr1-xBixFeO3 (x = 0.1, 0.3, 0.5) series, the oxygen flux increases with increasing Bi content. (C) 1998 Elsevier Science Ltd.

PREPARATION AND CHARACTERIZATION OF LANGMUIR-BLODGETT-FILMS OF PORPHYRINS WITHOUT LONG ALKYL CHAINS

A number of synthetic and natural source porphyrins without long alkyl chains have been examined in the form of monolayers and multilayers on solid substrates. These compounds formed stable solid condensed films with measured molecular areas compatible with a vertical or tilted orientation of these molecules on the substrate. Spectral study and fluorescence lifetime measurement, in particular, revealed the formation of aggregates as the main species in these films.

A novel method to synthesize amorphous silica-alumina materials with mesoporous distribution without using templates and pore-regulating agents

In this study, a novel sol-gel method is used to synthesize amorphous silica-alumina materials with a narrow mesoporous distribution and various Si/Al molar ratios without using any templates and pore-regulating agents. During the preparation procedure, only inexpensive inorganic salts were used as raw materials, instead of expensive and harmful alkoxides. The precursor sol was dried at room temperature in a vacuum box kept at 60 mmHg until it began to form the gel. The results of a nitrogen sorption experiment indicate that the synthesized materials with different Si/Al molar ratios have similar mesoporous distributions (within 2-12 nm). Moreover, it was found that the material's pore size distribution remains at a similar value during the heat treatment from room temperature to 550 degreesC. On the basis of the nitrogen sorption, TEM, and AFM characterization results, a formation mechanism of mesopores which accounts for the experimental data is also suggested. This suggested mechanism involves rearrangement of the primary particles during the drying process to form the precursors of the similarly sized mesopores. The synthesized materials were characterized by XRD, thermal analysis (TG/DTA), Al-27 and Si-29 MAS NMR spectroscopy, SEM, TEM, and AFM. The results of Al-27 and 29Si MAS NMR indicate that the distribution of silicon and aluminum in the synthesized materials is more uniform and homogeneous than that in the mixed oxides prepared via the traditional sol-gel method even at high alumina contents. The type and density of the acid sites were studied using pyridine adsorption-desorption FTIR spectroscopy. It was shown that the acidity of the synthesized materials is higher than that of the silica-alumina materials prepared by conventional methods.

Ultrasonic synthesis of silica-alumina nanomaterials with controlled mesopore distribution without using surfactants

A novel sol-gel process has been developed for the synthesis of amorphous silica-aluminas with controlled mesopore distribution without the use of organic templating agents, e.g., surfactant molecules. Ultrasonic treatment during the synthesis enables production of precursor sols with narrow particle size distribution. Atomic force microscopy analysis shows that these sol particles are spherical in shape with a narrow size distribution (i.e., 13-25 nm) and their aggregation during the gelation creates clusters containing similar sized interparticle mesopores. A nitrogen physiadsorption study indicates that the mesoporous materials containing different Si/Al ratios prepared by the new synthesis method has a large specific surface area (i.e., 587-692 m(2)/g) and similar pore sizes of 2-11 nm. Solid-state Al-27 magic angle spinning (MAS) NMR shows that most of the aluminum is located in the tetrahedral position. A transmission electron microscopy (TEM) image shows that the mesoporous silica-alumina consists of 12-25 nm spheres. Additionally, high-resolution TEM and electron diffraction indicate that some nanoparticles are characteristic of a crystal, although X-ray diffraction and Si-29 MAS NMR analysis show an amorphous material.