Hydrothermal synthesis of surface-modified iron oxide nanoparticles

We synthesized surface-modified iron oxide nanoparticles in aqueous phase by heating an aqueous solution of iron sulfate (FeSO₄) at 473 K with a small amount of either n-decanoic acid (C₉H₁₉COOH) or n-decylamine (C₁₀H₂₁NH₂), which is not miscible with water at room temperature. Transmission electron microscopy showed that the addition of n-decanoic acid or decylamine changed the shape of the obtained nanoparticles. X-ray diffraction spectra revealed that the synthesized nanoparticles were in α-Fe₂O₃ or Fe₃O₄ phase while Fourier transform infrared spectroscopy and thermogravimetry indicated the existence of an organic layer on the surface of the nanoparticles. In the synthetic condition, decreased dielectric constant of water at higher temperature increased the solubility of n-decanoic acid or n-decylamine in water to promote the reaction between the surface of iron oxide nanoparticles and the organic reagents. After the synthesis, the used organic modifiers separated from the aqueous phase at room temperature, which may help the environmentally benign synthesis of surface-modified metal oxide nanoparticles.     

Hydrothermal synthesis of sheaf-like CuO via ionic liquids

Sheaf-like CuO consisting of nanoplatelets were synthesized by a hydrothermal method at 100 °C from Cu(NO₃)₂·3H₂O and NaOH in the presence of an ionic liquid 1-butyl-3-methyl imidazolium tetrafluoroborate ([BMIM]BF₄). The XRD indicated the high crystal quality of CuO with monoclinic crystal structure. FESEM and TEM images showed the nanoplatelets with lengths of 4-5 μm, thickness of 65-80 nm and end angle of 60°. FTIR spectra and TG/DSC curves confirmed the adsorption of [BMIM]BF₄ on the surface of CuO. The morphology of CuO could be controlled by the feeding manner of [BMIM]BF₄. It was demonstrated that [BMIM]BF₄ served as a cosolvent and modifiers in the reaction system. Further, the possible growth mechanism of the sheaf-like CuO was proposed.     

Hydrothermal preparation of boehmite-doped AgCl nanocubes and their characterization

A simple hydrothermal route to the preparation of the boehmite-doped AgCl nanocubes using AgNO₃, AlCl₃·6H₂O and NaOH at 200 °C for 24 h is reported. The products were characterized by X-ray powder diffraction (XRD), Fourier transform infrared spectrometry (FT-IR), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), UV-vis, thermogravimetric analysis (TGA), and differential thermal analysis (DTA). FE-SEM and TEM micrographs showed that the obtained boehmite-doped AgCl had nanocube-like morphology. The influence of heating temperature on the phase, microstructure, morphology, and thermal stability of the products were also investigated. UV-visible results indicated that the absorption edge moved to higher wavelength with the increasing heating temperature. These materials would be a promising material for photocatalyst applications.     

Hydrothermal synthesis of GdBO3:Eu nanofibres

Large-scale GdBO₃:Eu³⁺ nanofibres with uniform diameter were controllably synthesized by a glycine-assisted hydrothermal method at 170 °C using Gd(NO₃)₃, Eu(NO₃)₃ and Na₂B₄O₇·10H₂O as the precursors. X-ray diffraction (XRD) results show that the luminescent nanofibres are pure hexagonal structure and no other impurity phase appeared. Transmission electron microscopy (TEM) studies indicate that GdBO₃:Eu³⁺ has a nanofibre structure. Photoluminescence (PL) spectra results demonstrate that the GdBO₃:Eu³⁺ nanofibres have three strong ⁵D₀ → ⁷F₁ (595 nm) and ⁵D₀ → ⁷F₂ (613 and 627 nm) transition peaks corresponding to orange-red and red colors, respectively.     

Synthesis of molybdenum oxide hollow microspheres by ethanol and PEG assisting hydrothermal process

Molybdenum oxide hollow microspheres were successfully synthesized via a combination of a hydrothermal method with ethanol and PEG assisting technique. The as-obtained products were characterized by SEM, XRD. The SEM results showed that the sizes of molybdenum oxide hollow spheres were 1-2 μm, and the spherical shape of the hollow microsphere products remained almost unaltered after calcination at 500 °C for 2 h. The XRD results showed that a purity phase of α-MoO₃ could be obtained after calcination. It was also found that the reaction temperature played a key role in the formation of hollow microshphere structure.     

Hydrothermal synthesis and characterization of MoS2 nanorods

MoS₂ nanorods were successfully synthesized via hydrothermal method by adding sillicontungstic acid as an additive. The products were characterized by X-ray powder diffraction (XRD), X-ray photoelectron spectrum (XPS) and field-emission scanning electron microscopy (FESEM). XRD pattern result indicated that the as-prepared sample can be indexed to a mixture of hexagonal and rhombohedral phase MoS₂. XPS showed that the nanorods were only composed of Mo and S with atomic ratio of 1:2. FESEM images revealed that the MoS₂ rods had uniform sizes with mean diameters of about 20-50 nm and lengths of 400-500 nm. It was found that the addition of sillicontungstic acid played a crucial role in the formation of the rod-like MoS₂ in our experiment. The possible formation mechanism of MoS₂ nanorods is also discussed.     

Hydrothermal synthesis and characterization of CePO4/C core-shell nanorods

The CePO₄/C nanocomposite with core-shell nanostructure has been successfully synthesized using glucose and CePO₄ by a facile and simple hydrothermal method at 160 °C for 24 h. The new material consists of a monoclinic CePO₄ core and an amorphous-C shell. The TEM micrograph indicated that the CePO₄/C nanocomposite was core-shell nanorods. The effects of glucose concentration on the C shells and luminescent intensity of CePO₄/C nanocomposite were investigated. The products were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL). This method is simple, low-cost and does not need any surfactant.     

Hydrothermal synthesis of fine oxide powders

This is a review and an overview on hydrothermal synthesis of fine oxide powders. The term hydrothermal today includes methods which involve water at pressures (from 1 atm-several kilobars) and high temperatures from 100–10,000°C. Hydrothermal is one of the best methods to produce pure fine oxide powders. The authors describe (i) hydrothermal decomposition, (ii) hydrothermal metal oxidation, (iii) hydrothermal reaction, (iv) hydrothermal precipitation and hydrothermal hydrolysis, (v) hydrothermal electrochemical, (vi) reactive electrode submerged arc, (vii) hydrothermal microwave, (viii) hydrothermal sonochemical, etc and also ideal and real powders     

Synthesis of transition metal-doped tungsten oxide nanostructures and their optical properties

In the present work, we report the solvothermal synthesis of transition metal-doped tungsten oxide nanostructures and their optical properties. Uniform, well-defined Co-doped tungsten oxide nanoblocks consisting of ultrathin nanowires, lenticular bundled Zn-doped tungsten oxide nanorods, and plate-shaped or flower-like Fe-doped tungsten oxide particles have been successfully prepared with the addition of different dopants. The doping of Co and Zn ions may prohibit the oriented growth of the tungsten oxide nanowires and favor their self-assembly, leading to the formation of bundled nanoblocks and nanorods. The Fe-doped tungsten oxide flowers may result from the ordered arrangement of single nanoplates. The band gaps of undoped, Fe-, Zn-, and Co-doped tungsten oxides are found to be 2.92, 2.78, 2.62, and 2.52 eV, respectively.     

Facile synthesis of MnCO3 hollow dumbbells and their conversion to manganese oxide

Manganese carbonate (MnCO₃) hollow dumbbells were synthesized via a polyol process. Based on the structural analysis of the samples obtained at different reaction times, a mechanism of nucleation-growth-aggregation-ripening was proposed to account for the formation of the hollow dumbbells. Moreover, the manganese oxide has also been obtained from the MnCO₃ crystals after thermal transformation in laboratory air, and the phase of final product could easily be controlled to be either MnO₂ or Mn₂O₃, simply by altering the calcination conditions. The manganese oxide powder products possessed mesoporosity and essentially preserved the pristine morphology of the MnCO₃ precursor.     

Hydrothermal synthesis of cuboidal PbSe microcrystals via an EDTA reduction route

Cuboidal lead selenide (PbSe) microcrystals have been successfully synthesized via a novel EDTA reduction route in which EDTA molecules serve as both chelating reagent and reductant. Hereafter EDTA is the abbreviation for ethylenediaminetetraacetic acid tetrasodium salt dihydrate (C₁₀H₁₂N₂Na₄O₈·2H₂O). The unique cuboidal PbSe microcrystals have eight symmetric arms along the < 111> directions. The edge of a cuboidal PbSe microcrystal extends outwards from its core with a tiny cubic center leaving step-like faces. The whole synthetic system provides an appropriate crystal growth environment for the formation of these microcrystals. Furthermore cuboidal PbSe microcrystals with different concave faces can be obtained at different reaction stages.     

Large-scale, hot-filament-assisted synthesis of tungsten oxide and related transition metal oxide nanowires

A scalable and versatile method for the large-scale synthesis of tungsten trioxide nanowires and their arrays on a variety of substrates, including amorphous quartz and fluorinated tin oxide, is reported. The synthesis involves the chemical-vapor transport of metal oxide vapor-phase species using air or oxygen flow over hot filaments onto substrates kept at a distance. The results show that the density of the nanowires can be varied from 10(6)-10(10) cm(-2) by varying the substrate temperature. The diameter of the nanowires ranges from 100-20 nm. The results also show that variations in oxygen flow and substrate temperature affect the nanowire morphology from straight to bundled to branched nanowires. A thermodynamic model is proposed to show that the condensation of WO(2) species primarily accounts for the nucleation and subsequent growth of the nanowires, which supports the hypothesis that the nucleation of nanowires occurs through condensation of suboxide WO(2) vapor-phase species. This is in contrast to the expected WO(3) vapor-phase species condensation into WO(3) solid phase for nanoparticle formation. The as-synthesized nanowires are shown to form stable dispersions compared to nanoparticles in various organic and inorganic solvents.     

Preparation of some transition metal sulphides

Ternary sulphides, LnMS₃ (Ln=rare earth metal; M=first row transition metal) and MV₂S₄ (M=Mg, Fe, Co, Ni and Zn) have been prepared by the reaction of appropriate ternary metal oxides with H₂S or CS₂/N₂ vapours at elevated temperatures. Chemical analysis and x-ray powder diffraction of the products indicate formation of single-phases with unique crystal structures in many cases. Communication No. 117 from the Solid State and Structural Chemistry Unit.     

Hydrothermal synthesis of CeO2 nano-octahedrons

CeO₂ nano-octahedrons were synthesized with a facile hydrothermal synthesis process where Ce(NO₃)₃·6H₂O and urea were used as a cerium resource and mineralizer respectively and no surfactant or template was applied. The effects of synthesis parameters such as reaction temperature, reaction time, as well as the dosages of Ce (NO₃)₃·6H₂O and urea were studied. X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis were conducted to characterize the crystalline and morphology of the obtained CeO₂ powders. The optimal reaction condition to prepare the CeO₂ of the desired fluorite structure was established. The possible mechanism of synthesis of CeO₂ with a nano-octahedron morphology was illustrated.     

Harmonic generation in transition metal dichalcogenides and their heterostructures

Few layered transition metal dichalcogenides (TMD), with an absence of crystal inversion symmetry and outstanding optical characteristics, are frequently applied in studies of nonlinear optics (NLO) for harmonic generation. Related materials are regarded as potential candidates for many optoelectronics applications. In order to enhance and manipulate the intrinsically weak NLO responses, TMD’s have been fabricated into heterostructures in recent years. The basic physics of harmonic generation and of TMD optical responses, as well as the interactions in TMD hybrid structures are introduced briefly, and the current state-of-the-art in the performance of TMDs in harmonic generation are reviewed. A particular focus is made on heterostructure studies to enhance and manipulate the response, which represent the core issues for devices and applications.     

Green synthesis of metal/C and metal oxide/C films by using natural membrane as support

A protocol aiming at making use of the huge amount of naturally existing wastes such as defoliation, pericarp and egg shell for nanostructured composite materials was proposed. In this study, a green synthetic route using naturally existing membrane as support was developed for the synthesis of nanostructured and porous metalor metal oxide-carbon composite films. Different metallic ions （Co2＋, Ni2＋, Fe3＋, Mn2＋ or Cu2＋） can be easily adsorbed onto egg membranes and the followed calcination process results in the formation of Co/C, Ni/C, Fe304/C, MnO/C or CulCu2OICuOIC composite films. The electrochemical studies demonstrate that such composite films would have potential applications in energy fields. This method would provide a general green concept for chemical synthesis and be beneficial to the global sustainable future.     

A novel solution method for selective synthesis of pure t-LaVO4

Tetragonal phase LaVO₄ (t-LaVO₄) was successfully selectively synthesized through a simple solution method with La(NO₃)₃ and NaVO₄ as starting materials without any templates or catalysts. The products were characterized by X-ray powder diffraction (XRD) and transmission electron microscopy (TEM). XRD patterns showed that pure t-LaVO₄ could be obtained in wide ranges of pH value and crystallization temperature. TEM images revealed that nanorods with different aspect ratios were obtained in different synthesis conditions. The shorter nanorods had mean diameters of about 18-25 nm and lengths of 40-60 nm. However, the longer nanorods had uniform sizes with an average aspect ratio about 10. It was interesting to discover that t-LaVO₄ could be formed even at room temperature (RT), which might be beneficial for a large scale production. Different luminescence performances of the samples doped 5% Eu³⁺ were also investigated.     

Hydrothermal synthesis of oriented MnS nanorods on anodized aluminum oxide template

High-density aligned MnS nanorods with a narrow length distribution were prepared on an anodized aluminum oxide (AAO) template under a hydrothermal condition. MnS nanomaterials with different shapes were obtained using different precursor concentrations in the reaction solution. The porous surface of the AAO template and the precursor concentrations may play key roles in the initial nucleation stage of growing oriented MnS nanorods.     

Hydrothermal synthesis of hexagonal ZnO clusters

Hydrothermal process was applied to synthesize zinc oxide nanocrystals. X-ray powder diffraction and scanning electron microscopy were used to analyze the crystal structure and surface morphology. XRD pattern analysis showed that the ZnO clusters are single hexagonal phase of wurtzite structure (space group P63 mc) with no impurity of Zn and Zn(OH)₂. Also, SEM images revealed that the size of a single ZnO crystal is between 200-500 nm in diameter and 2-5 μm in length. The influence of potassium iodide (KI) as a surfactant on the crystallinity of ZnO has been investigated.     

A novel solvothermal method to synthesize one-dimensional chains of indium tin oxide nanoparticles

One-dimensional conductive chains of indium tin oxide (ITO) nanoparticles with high specific surface areas of about 65 m² g^− 1 were synthesized from indium, tin acetylacetone complexes using isopropanol as solvent by a novel solvothermal method and post heat-treatment. When isopropanol was replaced with water as solvent, the non-conductive individual In₂SnO₅ nanoparticles were obtained.