Low-temperature hydrothermal synthesis of α-MnO2 three-dimensional nanostructures

Single-crystalline α-MnO₂ three-dimensional nanostructures were synthesized via a novel redox reaction of KMnO₄ and Cr(NO₃)₃ under hydrothermal conditions. The products were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy-dispersive spectroscopy (EDS), and high-resolution transmission electron microscopy (HRTEM). The addition of HNO₃ into the reaction has a significant effect on the morphologies of the final products. The α-MnO₂ three-dimensional nanostructures were obtained under the acidic condition, while α-MnO₂ nanowires were obtained without the addition of HNO₃. A mechanism for the growth of α-MnO₂ three-dimensional nanostructures was proposed.     

Morphological control of flower-like ZnO nanostructures

Flower-like ZnO nanostructures composed of different building blocks, such as hexagonal pyramids, hexagonal prisms, and cones, have been synthesized on a large scale by a simple hydrothermal method in the absence of surfactants or organic solvents. The effects of the concentration of NaOH, reaction temperature, and reaction time on the morphologies of the resulting products have been investigated. The morphologies and the crystal structures of flower-like ZnO nanostructures were characterized by X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM).     

Formation of novel assembled silver nanostructures from polyglycol solution

This paper described a simple and mild chemical reduction approach to prepare novel silver nanostructures with different morphologies. Dendritic silver nanostructure was obtained by a fast reduction reaction using hydrazine as a reducing agent in aqueous solution of polyglycol, while both the zigzag and linear Ag nanostructures were slowly assembled using polyglycol as a reducing agent. Powder X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution TEM (HRTEM) and field emission scanning electron microscopy (FE-SEM) were used to characterize the obtained silver nanostructures. Fourier transform infrared absorption (FT-IR) spectra were recorded to show that there exists a certain coordination of the oxygen atoms in the polyglycol with Ag⁺ ions in aqueous solution of the AgNO₃/polyglycol. Furthermore, the examination of the morphologies of the products obtained at different stages of the reaction of Ag⁺ ions with polyglycol revealed that such a coordination is of utmost importance for the formation of the silver nanostructures, namely polyglycol provided lots of active sites for the coordination, nucleation, growth and serves as backbones for directing the assembly of the metal particles formed. The formation mechanism of the dendritic silver nanostructure was called a coordination–reduction–nucleation–growth–fractal growth process. The strong surface plasmon absorption bands at 470 nm for the zigzag silver and at 405 nm for the dendritic silver were found.     

Impact of reaction temperature,stirring and cosolvent on the solvothermal synthesis of anatase TiO2 and TiO2/titanate hybrid nanostructures: Elucidating the growth mechanism

One-dimensional anatase TiO₂ and hybrid TiO₂/titanate nanostructures are synthesized by a simple low temperature solvothermal route followed by the Na⁺/H⁺ ion-exchange and final calcination process. We investigated the impact of reaction temperature, stirring conditions and cosolvent on the morphologies of the as-prepared nanostructures. Nanotubes and nanorods are formed in alkaline solution, while nanorods/nanowires and nanoporous nanoribbons are formed in alkaline water–ethanol and alkaline water–ethylene glycol mixed solvents, respectively. X-ray diffraction, Raman scattering and high-resolution transmission electron microscopy studies are employed to identify the structure and phase composition. The formation of different morphologies of the as-synthesized nanostructures is investigated by field emission scanning electron microscopy and transmission electron microscopy. The growth mechanism and reaction process of the as-prepared nanostructures are explained based on the experimental observations. The photoluminescence, optical absorption and the tuning of band gap of the prepared samples are also studied. This work will be valuable for understanding the growth mechanism of various nanostructured TiO₂ and to explore the commercial applications of nanoporous nanoribbons of TiO₂.     

Controllable synthesis of flower- and rod-like ZnO nanostructures by simply tuning the ratio of sodium hydroxide to zinc acetate

A controlled synthesis of flower-?and rod-like ZnO nanostructures in a hydrothermal phase has been realized in the absence of an additional template. The well-defined morphologies are obtained by simply tuning the ratio of sodium hydroxide to zinc acetate in a narrow range. The products are characterized by powder x-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The growth mechanism is suggested to be that the supersaturation of the precursor Zn(OH)(4)(2-) results in various nucleation habits, which induce the ZnO nanostructures with different morphologies.     

A simple route to V2O5·xH2O bundle-like nanostructures

V₂O₅·xH₂O bundle-like nanostructures composed of nanobelts have been synthesized by a simple hydrothermal method with the aid of Co²⁺. The widths, thickness and lengths of V₂O₅·xH₂O nanobelts are 80–100 nm, 10–20 nm, and several micrometers, respectively. The morphologies and the crystallographic structures of the V₂O₅·xH₂O bundle-like nanostructures were characterized by X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and electron diffraction (ED). The effects of the inorganic ions and reaction temperature on the morphologies of the resulting products have been investigated.     

Synthesis of aligned zinc sulfide nanostructures and the influence of experimental conditions on their morphologies and phase

A novel aligned flower-like array and single-crystal nanosheets composed of ZnS quantum wires were fabricated via a simple solution route. In the method, ZnCl2 chemicals reacted with Na2S in 50 ml of ethylenediamine (en) solution containing different amounts of hydrochloric acid (HCl) at 70-80 degrees C. After annealing at 500 degrees C for 1.5 h, wurtzite phase ZnS nanoscaled materials were synthesized. When the amount of HCl was 2 ml and 3 ml, respectively, flower-like structure and nanosheets were obtained. The products were characterized by X-ray diffraction, transmission electron microscopy, high-resolution electron microscopy (HREM), and electron diffraction (ED). The influences of concentration, temperature, and reaction time on the morphologies and phase of ZnS nanostructures were also studied. The photoluminescence peaks are located at approximately 308 nm and approximately 410 nm. The formation mechanism is also discussed here.     

Thermal Growth and Nanomagnetism of the Quasi-one Dimensional Iron Oxide

Quasi-one dimensional iron oxide nanowires with flat needle shape were synthesized on the iron powders by a rather simple catalyst-free thermal oxidation process in ambient atmosphere. The characterization by field emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman and high-resolution transmission electron microscopy (HRTEM) revealed that these nanostructures are single crystalline α-Fe2O3. The various dimensions with 40-170 nm in width and 1-8 μm in length were obtained by tuning the growth temperature from 280 to 480℃. A surface diffusion mechanism was proposed to account for the growth of quasi-one dimensional nanostructure. The typical α-Fe2O3 nanowires synthesized at 430℃ had a reduced Morin temperature TM of 131 K in comparison with their bulk counterpart. The coercivitis Hc of these nanowires are 321 and 65 Oe at 5 and 300 K, respectively. The temperature of synthesis also has important effects on the magnetic properties of these nanowires.     

Controllable synthesis of ZnO with various morphologies by hydrothermal method

ZnO microstructures with various morphologies have been controllably synthesized by hydrothermal route using different precipitant and zinc source in liquid solution. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize the ZnO2, Zn(OH)2 and ZnO structures to understand the role of precipitant and precursors in the growth of various morphologies. The nucleation and growth process can regulate by changing the precipitant. When H2O2 was used as precipitant, ZnO particles with a rather uniform particle size of -500 nm and a rather rough surface was obtained. While, ZnO synthesized in this polyvinyl pyrrolidone (PVP) solution has the same granular morphology with particle size of 300-1000 nm. In contrast, ZnO sunflower and polyhedron aggregates composed of several smaller polyhedron were formed, when ammonium hydroxide and NH4HCO3 was applied, respectively. Meanwhile, precursors play an important role in the determination of the morphology of ZnO. Sunflower and dumbbell like ZnO composed of nanosheets were obtained, when different centrifugal component of Zn(OH)2 suspension was applied as zinc source. In contrast, sunflower and dumbbell like ZnO composed of nanorods and ZnO rods were obtained, when different centrifugal components of ZnO2 suspension were used as zinc sources. The growth mechanism of ZnO nanostructures fabricated by the hydrothermal process using different zinc sources was tentatively investigated.     

D-penicillamine assisted hydrothermal synthesis of Bi2S3 nanoflowers and their electrochemical application

Single crystalline flower-like Bi₂S₃ nanostructures were successfully synthesized via a simple, facile and green hydrothermal method, with the assistance of D-penicillamine. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), and found their morphologies mainly depend on the ratios of Bi^3 + to D-penicillamine, as well as the reaction temperature and time. And the possible growth mechanism has been discussed in some detail. In addition, the as-prepared Bi₂S₃ nanoflowers show good hydrogen storage ability. This strategy can be potentially expanded to prepare other metal chalcogenides materials.     

磁性Fe3O4纳米颗粒的可控制备及生长研究

采用热法合成磁性Fe3O4纳米颗粒,通过精细调控实验条件能对其形状和大小进行有效控制。采用X射线衍射仪、透射电镜、振动样品磁强计等对Fe3O4纳米颗粒的成分、形貌及磁性等进行了表征测试。结果表明,Fe3O4纳米颗粒的饱和磁化强度为62.5emu/g。最后探讨了Fe3O4纳米颗粒的合成机理。     

Microwave synthesis and characterization of ZnO with various morphologies

ZnO micro- and nanostructures with a variety of morphologies have been synthesized using Zn(NO₃)₂·6H₂O and pyridine by a microwave-assisted aqueous solution method at 90 °C for 10 min. The pyridine has a significant influence on the morphology of ZnO. Various morphologies of ZnO (hexagonal columns, linked hexagonal needles, hollow structures, and hexagonal nanorings) were obtained by adjusting the concentration of pyridine. The effect of the type of other alkaline additive (aniline and triethanolamine) on the morphology of ZnO was also investigated. The products were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM).     

Direct observation of the growth process of MgO nanoflowers by a simple chemical route

Novel flowerlike nanostructures consisting of MgO nanofibers were successfully synthesized by a simple chemical route with H(2)O at 950 degrees C in an Ar atmosphere. Various durations of heating gave different growth stages that led to varied product morphologies. The synthesized products were systematically studied by X-ray powder diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, and energy-dispersive X-ray analysis. The results show that the nucleation and growth process of the nanoflowers seems to be a vapor-solid mechanism, and that the total heating time during the reaction process is a critical factor for the development of MgO nanoflowers. Initially, Mg particles formed on the Si substrate, followed by the formation of MgO clusters as nucleation centers on the magnesium melt surface and the nucleation of short MgO nanofibers, then growth of the MgO nanofibers occurred, and finally MgO nanoflowers were formed. Besides nanoflowers, novel hierarchical MgO nanostructures were also observed. These nanostructures may be used as three-dimensional composite materials and as supports for other materials.     

Fabrication, growth mechanism, and characterization of α-Fe(2)O(3) nanorods

This work reports the facile synthesis of α-Fe(2)O(3) nanorods and nano-hexagons and its application as sunlight-driven photocatalysis. The obtained products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), scanning electron microscopy (SEM), diffused reflectance spectroscopy (DRUV-vis), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The phase and crystallinity were confirmed from the XRD study. Electron microscopy study clearly indicates the formation of different morphologies of nanocrystals. These hematite nanostructures were used as a model system for studying the shape-dependent photocatalytic degradation of phenol, methylene blue, and congo red. Amongst all the nanostructured semiconductors, Pt-doped hematite nanorod showed 55% efficiency towards the decolonization of methylene blue and 63% toward congo red under sun light illumination. The difference in photocatalytic activity is discussed in terms of their crystallize size and morphological ordering.     

Silver nanocrystals of various morphologies deposited on silicon wafer and their applications in ultrasensitive surface-enhanced Raman scattering

Silver nanostructures with dendritic, flower-like and irregular morphologies were controllably deposited on a silicon substrate in an aqueous hydrogen fluoride solution at room temperature. The morphology of the Ag nanostructures changed from dendritic to urchin-like, flowerlike and pinecone-like with increasing the concentration of polyvinyl pyrrolidone (MW = 55,000) from 2 to 10 mM. The Ag nanostructures were characterized by transmission electron microscopy, high-resolution transmission electron microscopy, scanning electron microscopy, energy-dispersive X-ray, and X-ray diffraction. Through a series of time-dependent morphological evolution studies, the growth processes of Ag nanostructures have been systematically investigated and the corresponding growth mechanisms have been discussed. In addition, the morphology-dependent surface-enhanced Raman scattering of as-synthesized Ag nanostructures were investigated. The results indicated that flower-like Ag nanostructure had the highest activity than the other Ag nanostructures for Rhodamine 6G probe molecules.     

Morphology controllable synthesis of TiO2 by a facile hydrothermal process

Titanium dioxide nanoparticles were prepared via a facile hydrothermal approach with titanium tetrabutoxide as a precursor under strongly acidic condition. The transmission electron microscopy results showed that novel flower-like, leaf-like, and rod-like TiO₂ nanoscale materials could be easily obtained by tailoring the concentration of the precursor and the reaction temperature. And the analysis from X-ray diffraction revealed that all the as-prepared products under different experimental conditions possessed a mixed crystal phase of anatase and rutile. The reasons for the phase formation were discussed. Larger proportion of rutile phase should be ascribed to the strongly acidic conditions. The growth mechanisms of TiO₂ nanostructures with various morphologies were also proposed.     

Controllable synthesis of hierarchical nanostructures of CaWO4 and SrWO4 via a facile low-temperature route

CaWO₄ and SrWO₄ nanostructures have been synthesized via a simple microemulsion-mediated route. With careful control of the fundamental experimental parameters including the concentration of reactants, the reaction time and the temperature, the products with different morphologies of dumbbell, coral, rod and dendrite have been obtained, respectively. The possible formation mechanism of these unique morphologies has been proposed based on surfactant self-assembly under different experimental conditions. The as-synthesized CaWO₄ samples with various morphologies exhibit different photoluminescence properties. X-ray powder diffraction, transmission electron microscopy, field-emission scanning electron microscopy, and luminescence spectroscopy were used to characterize these products.     

Preparation of highly ordered growth of single-crystalline Gd2O2S:Eu nanostructures

A simple and facile template-assisted hydrothermal route has been demonstrated for the shape-selective preparation of highly ordered single-crystalline Gd₂O₂S:Eu³⁺ nanostructures, such as nanotubes, nanorods and nanoflowers. These fabricated nanostructures possess desirable atomic structures, surfaces, morphologies and properties to meet the growing demands and specific requirements of new technologies. The concentration of precursor chemicals, the temperature, the reaction time, and the use of a capping agent are key factors in the morphological control of Gd₂O₂S:Eu³⁺ nanostructures. The morphology and the phase composition of the prepared nanostructures were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), energy disperse spectroscopy (EDS) and photoluminescence (PL). We believe this technique will be readily adopted in realizing other forms of various nanostructured materials.     

Synthesis of carbon nanostructures by graphite deformation during mechanical milling in air

Abstract

In this investigation, time-dependent carbon nanostructures were prepared by high-energy ball milling in the air from elemental graphite powders. Scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy (RS), and high-resolution transmission electron microscopy (HRTEM) characterized the ball-milled powders. XRD analysis showed that the crystal size decreased with the milling time. Raman spectra confirmed the presence of carbon nanostructures with sp² hybridization. Meanwhile, HRTEM images revealed different carbon morphologies during the milling time. During the different stages, it appears distortion of layers, large tapes, polyhedral morphologies, nanocapsules, and nano-onions. These carbon nanostructures occur in regions where there is carbon accumulation. In this way, the ball milling process in air conditions can promote distorted carbon and different morphologies.     

Optical and bio-sensing characteristics of ZnO nanotubes grown by hydrothermal method

ZnO nanostructures were fabricated on copper substrates by hydrothermal method at an optimized growth temperature of -95 degrees C. Structural properties were investigated by field emission scanning electron and transmission electron microscopy. Distinct morphologies were found to be formed at different growth times. The formation of nanotubes mainly involved the initial nucleation followed by the growth of nanorods at 95 degrees C, and then with the increase of dissolution time at room temperature, the preferential chemical dissolution of the metastable Zn-rich [0001] polar surfaces resulted in removing the atoms from the surfaces, thus leading to the thinning of the wall of the nanostructures. Completely hollow ZnO nanotubes could be obtained at a high dissolution time. The room temperature photoluminescence and optical absorption properties of ZnO nanotubes have been studied as a function of dissolution time. The efficacy of ZnO nanotubes for glucose sensing applications has been studied.