Papers by Keyword: Hydrothermal Synthesis

Abstract: The phase equilibrium of the LiCl-MgCl₂-Na₂­SiO₃-H₂O (LMNH) quaternary system at 150°C was studied and the phase diagram of the system was plotted, in order to synthesize hectorite with the nature brine, which was rich in lithium and magnesium. The solid phases were characterized by X-ray diffraction (XRD) and Energy Dispersive Spectrometer (EDS). It was found that hectorite, lithium silicate, karpinskite and brucite can be formed in this system.

Abstract: Vanadium dioxides (VO₂) is synthesized by hydrothermal method. In this process,V₂O₅ powder is used as raw materials,cetyltrimethylammonium bromide (CTAB) is used as template and different alcohols such as methanol, ethanol, propanol and butanol are used as reductants. X-ray diffraction (XRD) and scanning electron microscopy (SEM) are used to test the properties of VO₂ nanoparticles. The results show that VO₂(B) nano-particles were succsessfully synthesized under the conditions of thermal reduction temperature 180°C, reaction time 24h and drying temperature 60°C. The variety of alcoholic reducing agents plays an important role in the structure and morphology of the product VO₂(B), which relates closly to the electric properties of materials.

Abstract: LaPO₄:Eu³⁺ nanoparticles were prepared by the hydrothermal synthesis method at different temperatures. The phase composition and microstructure of nanoparticles were characterized by XRD (X-ray diffraction) and SEM (Scanning electron microscopy), respectively. The results reveal that the phase composition of the powders is dependent on the water bath temperature but the microstructure has little effect. The doped powders can be well crystallized at 120°C with the hexagonal monazite-type structure of the LaPO₄ phase. The monoclinic structure of LaPO₄ phase generated as the temperature increases. The sample has pure monoclinic structure of LaPO₄ phase when the temperature increased to 200°C. It has been shown that all the nanocrystals obtained at different temperatures present a long rod-like shape. The analysis of the fluorescence spectra shows that the luminous intensity of the monoclinic structure of LaPO₄:Eu³⁺ is stronger than the hexagonal structure.

Abstract: The manganese oxide (MnO₂) nanocrystals were formed on the surface of graphene oxides (GOs) and multi−walled carbon nanotubes (MWCNTs) through a facial hydrothermal route, respectively. It is found that the similar flower−like MnO₂ nanocrystals covered on both conductive supports. Moreover, more dense and less size of MnO₂ nanocrystals appeared on the surface of MWCNTs, whereas more perfect crystal structures for MnO₂/GOs. Electrochemical measurements showed that both the nanocomposite electrodes exhibited nearly ideal capacitive behavior, and large capacitive value can be obtained for MnO₂/GOs, while high stability for MnO₂/MWCNTs. The high capacitance performance arises from the unique nanostructure of the nanocrystals, which facilitate the contact of the electrolyte and the active materials, and carbon−based materials provide an effective support for the formation of the nanocrystals and conductive pathway for the nanocomposite electrodes.

Abstract: The flower-sphere molybdenum disulfide has been synthesized by reaction of Na₂MoO₄ and CS(NH₂)₂ with NH₂OH·HCl or H₂C₂O₄ as reductant. The microstructure and chemical composition of the product were characterized by means of X-ray diffraction and scanning electron microscope. XRD patterns showed that the molar ratio of Mo to S had a great effect on the purity of the product. When the molar ratio of Mo to S was 1:5, the product was nearly pure MoS₂. SEM images showed that the particle size increased as the molar ratio of Mo to S reduced. The MoS₂ microspheres had rough surfaces and were constructed with sheet-like structures in the two systems. But the product from the system of NH₂OH·HCl as reductant has the bigger particle size, clearer petal-sheets, coarser surface and weaker agglomeration than that from the system H₂C₂O₄ as reductant. The possible chemical reactions in hydrothermal systems were preliminarily discussed.

Abstract: The VO2(B) nanobelts with monoclinic phase were synthesized by a hydrothermal method at 220°C for 48 h in the absence of any surfactants. The electron energy loss spectrum (EELS) demonstrates that vanadium exists only in the 4+ oxidation state. The SEM and TEM images reveal a belt-like structure of the VO2(B) with the length of several micrometers, the width of 140 nm and the thickness of around 20nm and growth along the [110] crystal direction. Cyclic voltammetry (CV) and galvanostatic charge/discharge demonstrate that VO2(B) nano-belts electrode exhibits desirable electrochemical properties and the specific capacitance reaches up to 632.6F•g-1.

Abstract: Pure and Cobalt-doped ZnO nanostructures have been synthesized by a hydrothermal process. The samples were characterized by X-ray diffraction (XRD), UV-Vis diffusion reflectance spectra (DRS) and X-ray energy dispersion spectroscopy (EDS). The structure and morphology analyses show that Co doping can influence the nanostructures morphology, but cannot change the crystal structures of ZnO samples. The DRS spectra showed that Co dopant enhanced the ability of visible light absorption of the ZnO samples

Abstract: ZnO nanostructures with different morphology were successfully prepared via a hexamethylendiamine-assisted hydrothermal synthesis route by only adjusting reaction temperature. The prepared ZnO samples were characterized by powder X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and high resolution TEM (HRTEM). Results indicated that uniform flake-like ZnO nanoparticles with a similar thickness of about 70 nm and flower-like ZnO nanostructures assembled by prism-like nanorods were prepared at 120 °C and 180 °C, respectively. Possible mechanisms for the formation of ZnO with different morphologies were discussed. The photocatalytic properties of the as-prepared flake-like ZnO nanoparticles and flower-like ZnO nanostructures were studied.

Abstract: The effect of mineralizer upon the fabrication of lead-free, piezoelectric Bi0.5Na0.5TiO3 ( BNT) was investigated using a hydrothermal reaction technique. Results indicated that BNT crystals can be formed in a basic environment controlled by a NaOH mineralizer. The morphologies and sizes of the resultant particles are determined by the concentration of NaOH: a lower alkaline concentration leads to the particles with a spherical shape consisting of a number of small, intergrown BNT crystals while a higher NaOH concentration (e.g. > 12 mol/L) results in large, individual BNT cubes. Possible growth mechanisms of the BNT particles were discussed in conjunction with surface hydration, dehydration and free water content during the hydrothermal reaction.

Abstract: In the work, nano-sized MoO₃ and unsupported MoS₂ hydro desulfurization catalysts were synthesized using a novel hydrothermal reduction method. The influences of the temperature and the synthetic methods on the growth morphology of molybdenum disulfide were systematically investigated. It was found that the MoS₂ fibers were easy to be bended and had lots of defects, which increased the number of active sites on the catalyst and easily met the requirements of deep hydrotreating desulfurization of diesel oil.