Preparation of Monolithic LaFeO3 and Catalytic Oxidation of Toluene.

Porous LaFeO3 powders were produced by high-temperature calcination of LaFeO3 precursors obtained by hydrothermal treatment of corresponding nitrates in the presence of citric acid. Four LaFeO3 powders calcinated at different temperatures were mixed with appropriate amounts of kaolinite, carboxymethyl cellulose, glycerol and active carbon for the preparation of monolithic LaFeO3 by extrusion. Porous LaFeO3 powders were characterized using powder X-ray diffraction, scanning electron microscopy, nitrogen absorption/desorption and X-ray photoelectron spectroscopy. Among the four monolithic LaFeO3 catalysts, the catalyst calcinated at 700 °C showed the best catalytic activity for the catalytic oxidation of toluene at 36,000 mL/(g∙h), and the corresponding T10%, T50% and T90% was 76 °C, 253 °C and 420 °C, respectively. The catalytic performance is attributed to the larger specific surface area (23.41 m2/g), higher surface adsorption of oxygen concentration and larger Fe2+/Fe3+ ratio associated with LaFeO3 calcined at 700 °C.

Preparation and Photocatalytic Performance of MoS2/MoO2 Composite Catalyst.

Solar energy is an inexhaustible clean energy providing a key solution to the dual challenges of energy and environmental crises. Graphite-like layered molybdenum disulfide (MoS2) is a promising photocatalytic material with three different crystal structures, 1T, 2H and 3R, each with distinct photoelectric properties. In this paper, 1T-MoS2 and 2H-MoS2, which are widely used in photocatalytic hydrogen evolution, were combined with MoO2 to form composite catalysts using a bottom-up one-step hydrothermal method. The microstructure and morphology of the composite catalysts were studied by XRD, SEM, BET, XPS and EIS. The prepared catalysts were used in the photocatalytic hydrogen evolution of formic acid. The results show that MoS2/MoO2 composite catalysts have an excellent catalytic effect on hydrogen evolution from formic acid. By analyzing the photocatalytic hydrogen production performance of composite catalysts, it suggests that the properties of MoS2 composite catalysts with different polymorphs are distinct, and different content of MoO2 also bring differences. Among the composite catalysts, 2H-MoS2/MoO2 composite catalysts with 48% MoO2 content show the best performance. The hydrogen yield is 960 µmol/h, which is 1.2 times pure 2H-MoS2 and two times pure MoO2. The hydrogen selectivity reaches 75%, which is 22% times higher than that of pure 2H-MoS2 and 30% higher than that of MoO2. The excellent performance of the 2H-MoS2/MoO2 composite catalyst is mainly due to the formation of the heterogeneous structure between MoS2 and MoO2, which improves the migration of photogenerated carriers and reduces the possibilities of recombination through the internal electric field. MoS2/MoO2 composite catalyst provides a cheap and efficient solution for photocatalytic hydrogen production from formic acid.

Hydrothermal Synthesis of MoS2/SnS2 Photocatalysts with Heterogeneous Structures Enhances Photocatalytic Activity.

The use of solar photocatalysts to degrade organic pollutants is not only the most promising and efficient strategy to solve pollution problems today but also helps to alleviate the energy crisis. In this work, MoS2/SnS2 heterogeneous structure catalysts were prepared by a facile hydrothermal method, and the microstructures and morphologies of these catalysts were investigated using XRD, SEM, TEM, BET, XPS and EIS. Eventually, the optimal synthesis conditions of the catalysts were obtained as 180 °C for 14 h, with the molar ratio of molybdenum to tin atoms being 2:1 and the acidity and alkalinity of the solution adjusted by hydrochloric acid. TEM images of the composite catalysts synthesized under these conditions clearly show that the lamellar SnS2 grows on the surface of MoS2 at a smaller size; high-resolution TEM images show lattice stripe distances of 0.68 nm and 0.30 nm for the (002) plane of MoS2 and the (100) plane of SnS2, respectively. Thus, in terms of microstructure, it is confirmed that the MoS2 and SnS2 in the composite catalyst form a tight heterogeneous structure. The degradation efficiency of the best composite catalyst for methylene blue (MB) was 83.0%, which was 8.3 times higher than that of pure MoS2 and 16.6 times higher than that of pure SnS2. After four cycles, the degradation efficiency of the catalyst was 74.7%, indicating a relatively stable catalytic performance. The increase in activity could be attributed to the improved visible light absorption, the increase in active sites introduced at the exposed edges of MoS2 nanoparticles and the construction of heterojunctions opening up photogenerated carrier transfer pathways and effective charge separation and transfer. This unique heterostructure photocatalyst not only has excellent photocatalytic performance but also has good cycling stability, which provides a simple, convenient and low-cost method for the photocatalytic degradation of organic pollutants.

Three-dimensional ZnO@MnO2 core@shell nanostructures for electrochemical energy storage.

Three-dimensional (3D) ZnO@MnO2 core@shell branched nanowire arrays exhibit five times higher areal capacitance, better rate performance and smaller inner resistance than their nanowire array counterparts. These novel 3D architectures offer promising designs for powering microelectronics and other autonomous devices on exceptionally small geometric scales.

The complete control for the nanosize of spherical MCM-41.

In this work, we present a systematic study on the complete control over the sphere diameters of MCM-41 nanospheres with different pore sizes. The mesoporous silica nanospheres with diameter range from 40 nm to 160 nm are synthesized by using cationic quaternary ammonium surfactants as template and TEOS as silicon source in sodium hydroxide aqueous solution via sol-gel supermolecular method. Nanospheres with fixed diameter can be obtained through the precise control over the molar ratio of NaOH/TEOS and other synthetic conditions. The range of sphere diameter for each sample prepared under adjustable reaction conditions is in a sharp distribution. Moreover, the formation mechanism for nanospheres with controlled morphological and structural features is proposed, and we suggest the optimal synthesis conditions of the MCM-41 nanospheres for the minimization of the Gibbs free energy deltaG. Besides, after depositing vanadium species on the MCM-41 support, the catalytic performance of V-MCM-41 for the selective oxidation of styrene by hydroperoxide increases with the diameter of the supports decreasing.

Surfactant-free microwave-assisted hydrothermal synthesis of BaMoO4 hierarchical self-assemblies and enhanced photoluminescence properties.

BaMoO(4) with 3D hierarchical multilayer disk-like and nest-like architectures self-assembled from 2D nanosheets was successfully synthesized via a microwave-assisted hydrothermal route without any surfactant. The as-prepared products were characterized by X-ray powder diffractometer (XRD), scanning electron microscope (SEM), field emission transmission electron microscope (FE-TEM), and photoluminescence (PL) spectrometer. The results show that the reaction parameters, including pH value, reactant concentration, and molar ratio of [Ba(2+)]/[MoO(4)(2-)], played important roles on the morphologies of the final products. And the formation mechanism of 3D hierarchical architectures is a stepwise oriented aggregation-based self-assembly process. The superstructure characteristic of 3D nest-like BaMoO(4) architecture was observed in HRTEM image and the corresponding fast Fourier transform (FFT) for the first time, and the superlattice reflections with non-integer indices occurred around the subcell reflections at ±1/6(2a*+2c*). Room temperature photoluminescence spectra of 3D BaMoO(4) architectures reveal a strong and broad blue emission, and the 3D nest-like architectures own the enhanced intensity than multilayer disks.

Growth and characterization of ternary AlGaN alloy nanocones across the entire composition range.

AlGaN ternary alloys have unique properties suitable for numerous applications due to their tunable direct band gap from 3.4 to 6.2 eV by changing the composition. Herein we report a convenient chemical vapor deposition growth of the quasi-aligned Al(x)Ga(1-x)N alloy nanocones over the entire composition range. The nanocones were grown on Si substrates in large area by the reactions between GaCl(3), AlCl(3) vapors, and NH(3) gas under moderate temperature around 700 °C. The as-prepared wurtzite Al(x)Ga(1-x)N nanocones have single-crystalline structure preferentially growing along the c-axis, with homogeneous composition distribution, as revealed by the characterizations of electron microscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy, and selected area electron diffraction. The continuous composition tunability is also demonstrated by the progressive evolutions of the band edge emission in cathodoluminescence and the turn-on and threshold fields in field emission measurements. The successful preparation of Al(x)Ga(1-x)N nanocones provides the new possibility for the further development of advanced nano- and opto-electronic devices.

Preparation of Eu(3+) doped (Y,Gd)(2)O(3) flowers from (Y,Gd)(2)(CO(3))(3).nH(2)O flowerlike precursors: Microwave hydrothermal synthesis, growth mechanism and luminescence property.

In this study, (Y,Gd)(2)O(3) and (Y,Gd)(2)O(3):Eu flowerlike microstructures were prepared through two steps: well-organized 3-dimensional (3D) flowerlike precursors were first synthesized by a facile urea-based microwave hydrothermal method, then followed by heat treatment. The morphology of the 3D flowerlike precursors could be modulated by adjusting the synthetic conditions including concentration of the starting material, reaction time and temperature. Higher the concentration of Y/Gd ions or reaction temperature, earlier the 3D flowerlike precursors were obtained. The samples were characterized by various means. The flowers were found to derive from colloidal spheres, which experienced a dissolution/crystalline, attachment and self-assembly process. Room temperature photoluminescence spectrum of 3D flowerlike (Y,Gd)(2)O(3):Eu showed enhanced emission property than the spheres.

A novel ZnO nanostructure: rhombus-shaped ZnO nanorod array.

A facile scalable two-step approach based on a low-temperature aqueous electrodeposition and a solid-state crystal phase transformation process was developed to grow rhombus-shaped ZnO nanorod arrays which showed markedly improved hydrogen storage capacity.

Construction of uric acid biosensor based on biomimetic titanate nanotubes.

A uric acid biosensor has been fabricated through the immobilization of uricase on glassy carbon electrode modified by biomimetic titanate nanotubes of high specific surface area synthesized by hydrothermal decomposition. The so-constructed biosensor presents a high affinity to uric acid with a small apparent Michaelis-Menten constant of only 0.66 mM. The biosensor exhibits fairly good electrochemical properties such as the high sensitivity of 184.3 microAcm(-2)mM(-1), the fast response of less than 2 s, as well as the wide linear range from 1 microM to 5 mM. These performances indicate that titanate nanotubes could provide a favorable microenvironment for uricase immobilization, stabilize its biological activity, and function as an efficient electron conducting tunnel to facilitate the electron transfer. This suggests an important potential of titanate nanotubes in uric acid biosensors.

Facile Construction of Pt-Co/CNx Nanotube Electrocatalysts and Their Application to the Oxygen Reduction Reaction.

A straight forward method for immobilizing Pt-Co alloyed nanoparticles onto nitrogen-doped CNx nanotubes is presented. The as-prepared electrocatalysts exhibit good performance for oxygen reduction reaction in acidic medium arising from the high-dispersion and alloying effect of the Pt-Co nanoparticles and the intrinsic catalytic capacity of the CNx nanotubes.

Electrocatalysts: Facile Construction of Pt-Co/CNx Nanotube Electrocatalysts and Their Application to the Oxygen Reduction Reaction (Adv. Mater. 48/2009).

Pt-Co alloyed nanoparticles can be facilely immobilized onto CNx nanotubes due to the incorporated nitrogen, report Yanwen Ma, Zheng Hu, and co-workers on p. 4953. The as-prepared electrocatalysts exhibit good performance for oxygen reduction reactions in acidic media arising from the high dispersion and alloying effect of Pt-Co nanoparticles, as well as the intrinsic catalytic capacity of CNx nanotubes, which is significant for the development of fuel cells.

A highly ordered self-assembly three-grade porous helical silica tube.

A novel three-grade porous helical silica tube is prepared through an ingenious multi-soft-template pathway. This study reveals that three-(or multi-)grade self-assembly porous structure can be realized by using the synergistic effect of soft-templates. Our finding can offer an opportunity for nanofabrication including rational molecular design, spatial control on a nanoscale, and hierarchical assembly of complex architectures of porous materials.

Synthesis and field emission characterization of titanium nitride nanowires.

Single crystalline titanium nitride nanowires have been successfully synthesized through a chloride-assisted carbon thermal reduction method using the active carbon, TiO2 and NaCl powders as precursors and cobalt nanoparticles as catalyst. The products were characterized by X-ray diffraction, electron microscopy, and energy-dispersive X-ray spectroscopy. The TiN nanowires possess a cubic structure with typical diameter of 20-60 nm and length up to microns. The field emission property of the TiN nanowires has been characterized for the first time, which follows the conventional Fowler-Nordheim behavior and shows the low turn-on field of 7.1 V microm-1 and good emission stability, indicating the potential applications. The formation mechanism of the TiN nanowires has also been discussed.

Chemical functionalization of magnetic carbon-encapsulated nanoparticles based on acid oxidation.

Carbon-encapsulated nickel nanoparticles were used as the representative magnetic carbon-encapsulated nanoparticles for chemical functionalization. After oxidation with the mixed acid of H2SO4/HNO3 under a moderate ultrasonic bath, carboxylic acid groups (-COOH) were effectively generated on the fullerene-like carbon shells, which in turn were utilized to covalently link octadecylamine through an amide reaction. The whole chemical process is well characterized by many methods such as Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, thermogravimetry-differential scanning calorimetry, transmission electron microscopy, and so on, and the self-consistent experimental results were obtained. The results suggested that the magnetic nanoparticles could be well protected, while their magnetic properties could be utilized to guide the transfer of the grafted functional species on the particle surface. This provides many possibilities for potential applications in chemical and biochemical fields.

Synergism of C5N six-membered ring and vapor-liquid-solid growth of CN(x) nanotubes with pyridine precursor.

A series of bamboo-like CN(x)() nanotubes have been synthesized from pyridine precursor by chemical vapor deposition with bimetallic Fe-Co/gamma-Al(2)O(3) catalyst in the range of 550 approximately 950 degrees C. An unusual predomination of pyridinic nitrogen over graphitic nitrogen has been observed for the CN(x)() nanotubes with reaction temperature below 750 degrees C. The pyridinic nitrogen decreases and the graphitic nitrogen increases with rising reaction temperature. A synergism mechanism of C(5)N-six-membered-ring-based growth through surface diffusion and vapor-liquid-solid growth through bulk diffusion was accordingly deduced and schematically presented. This mechanism could not only explain our own experimental results, but also understand the CN(x)()-nanotube-related experimental phenomena in the literature, as well as be in accordance with the basic principle of diffusion kinetics. A promising route to the challenging topic for synthesizing regularly arranged C(5)N or high-N-content CN(x)() nanotubes has also been suggested.

Synthesis and optical properties of gallium phosphide nanotubes.

Gallium phosphide nanotubes with zinc blende structure were synthesized for the first time. The as-prepared GaP nanotubes are polycrystalline with diameters of 30-120 nm and occasionally partially filled. The growth has been reasonably proposed to follow vapor-liquid-solid (VLS) mechanism. The integration of the nanotubular structure with the unique intrinsic semiconducting properties of GaP might bring GaP nanotubes some novel optical and electronic properties and applications.

Synthesis of single-crystalline alpha-Si(3)N(4) nanobelts by extended vapour-liquid-solid growth.

A simple chemical method for the production of single-crystalline alpha-Si(3)N(4) nanobelts has been developed, consisting of nitridation of a high-Si-content Fe-Si 'catalyst' by ammonia at 1300 degrees C. The as-synthesized product was characterized by means of x-ray diffraction, electron microscopy and energy-dispersive x-ray spectroscopy. The alpha-Si(3)N(4) nanobelts have widths of 60-120 nm, thicknesses of 10-30 nm and lengths up to microns. Four intense green-blue luminescence bands at 398 nm (3.12 eV), 434 nm (2.86 eV), 492 nm (2.52 eV) and 540 nm (2.30 eV) were observed and analysed for the product, which indicates the potential applications in optoelectronics. The growth mechanism has also been speculated upon. The potential technological importance of the product, the simplicity of the preparation procedure, as well as the cheap commercial precursor of Fe-Si alloy particles makes this study both scientifically and technologically interesting.

Sonochemical fabrication and characterization of stibnite nanorods.

Regular stibnite (Sb(2)S(3)) nanorods with diameters of 20-40 nm and lengths of 220-350 nm have been successfully synthesized by a sonochemical method under ambient air from an ethanolic solution containing antimony trichloride and thioacetamide. The as-prepared Sb(2)S(3) nanorods are characterized by employing techniques including X-ray powder diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, energy-dispersive X-ray analysis, transmission electron microscopy, selected area electron diffraction, high-resolution transmission electron microscopy, and optical diffuse reflection spectroscopy. Microstructural analysis reveals that the Sb(2)S(3) nanorods crystallize in an orthorhombic structure and predominantly grow along the (001) crystalline plane. High-intensity ultrasound irradiation plays an important role in the formation of these Sb(2)S(3) nanorods. The experimental results show that the sonochemical formation of stibnite nanorods can be divided into four steps in sequence: (1) ultrasound-induced decomposition of the precursor, which leads to the formation of amorphous Sb(2)S(3) nanospheres; (2) ultrasound-induced crystallization of these amorphous nanospheres and generation of nanocrystalline irregular short rods; (3) a crystal growth process, giving rise to the formation of regular needle-shaped nanowhiskers; (4) surface corrosion and fragmentation of the nanowhiskers by ultrasound irradiation, resulting in the formation of regular nanorods. The optical properties of the Sb(2)S(3) amorphous nanospheres, irregular short nanorods, needle-shaped nanowhiskers, and regular nanorods are investigated by diffuse reflection spectroscopic measurements, and the band gaps are measured to be 2.45, 1.99, 1.85, and 1.94 eV, respectively.