Preparation of Spherical Tungsten Particles Assisted by Hydrothermal Method

We presented a strategy to prepare spherical tungsten powder by the combination of hydrothermal method and H2reduction process.In hydrothermal process,the micelle of tetraethylammonium bromide(TEAB)act as spherical templates for the deposition of tungsten oxide,whereas the excessive TEAB inhibit the formation of spherical tungsten oxide due to the dense molecular layer of TEAB on the tungsten oxide particles.Citric acid(CA)can control the formation rate and structure of the tungsten oxide when its concentration is more than 0.2 mol/L,because of its ability to coordinate with tungsten atoms.The synergistic effect of TEAB and CA facilitates the formation of spherical tungsten oxide with nanorod crown.After being treated by H_(2)at 600 and 650℃,the tungsten oxide particles are reduced to tungsten particles,which maintain the spherical structure of tungsten oxide and have porous structure.

Structural, Optical and Photocatalytic Properties of Cu2+ Doped ZnO Nanorods with Using HMTA Solvent Prepared by Hydrothermal Method

In this experiment, Cu2+ doped ZnO (Cu-ZnO) nanorods materials have been fabricated by hydrothermal method. Cu2+ ions were doped into ZnO with ratios of 2, 5 and 7 mol.% (compared to the mole’s number of Zn2+). The hexamethylenetetramine (HMTA) solvent used for the fabrication of Cu-ZnO nanorods with the mole ratio of Zn2+:HMTA = 1:4. The characteristics of the materials were analyzed by techniques, such as XRD, Raman shift, SEM and UV-vis diffuse reflectance spectra (DRS). The photocatalytic properties of the materials were investigated by the decomposition of the methylene blue (MB) dye solution under ultraviolet light. The results show that the size of Cu-ZnO nanorods was reduced when the Cu2+ doping ratio increased from 2 mol.% to 7 mol.%. The decomposition efficiency of the MB dye solution reached 92% - 97%, corresponding to the Cu2+ doping ratio changed from 2 - 7 mol.% (after 40 minutes of ultraviolet irradiation). The highest efficiency for the decomposition of the MB solution was obtained at a Cu2+ doping ratio of 2 mol.%.

Synthesis of MnZn Ferrite Nanoscale Particles by Hydrothermal Method

Hydrothermal method was used to synthesize nanoscale particles of MnZn ferrites. The crystallites were characterized by XRD, TEM and SEM. The effects of the reaction time, temperature and additives on the product were investigated. Crystallization process would be carried out above 160 ℃ for 5 h or more, higher temperature can reduce the reaction time. Additives were used to remove impurities such as Fe 2O 3, ZnMnO 3.10～15 nm pure slightly agglomerated MnZn ferrite crystallites with a narrow grain size distribution were obtained.

Synthesis and electrochemical performance of LiCoPO_4 micron-rods by dispersant-aided hydrothermal method for lithium ion batteries

LiCoPO4 micron-rods with an average diameter of about 500 nm and length of about 5 μm were synthesized by dispersant-aided hydrothermal method. Poly(n-vinylpyrrolidone) (PVP) was used as dispersant in the hydrothermal method. The starting solution and the concentration of dispersant have significant influences on the morphology of LiCoPO4,and the electrochemical performance is improved via controlling the particle size and morphology by the hydrothermal method. The cell using smaller particle LiCoPO4 as cathode delivers a larger capacity and lower cell polarization.

Upconversion Luminescence Properties of Ho^(3+),Tm^(3+),Yb^(3+) Co-Doped Nanocrystal NaYF_4 Synthesized by Hydrothermal Method

Nanocrystal of upconversion （UC） phosphor Ho^3＋, Tm^3＋ , and Yb^3＋ co-doped NaYF4 was prepared by the hydrothermal method in the presence of the complexing agent EDTA. Under 980 nm diode laser excitation, the impact of different concentrations of Ho^3＋ ion on the UC luminescence intensity was discussed. The law of luminescence intensity versus pump power shows that the 474 nm blue emission, 538 nm green emission, and 642 nm red emission are all due to the two-photon process, while the 450 nm blue emission is a three-photon process. The UC mechanism and processes were also analyzed. The sample was characterized by transmission electron microscopy （TEM） and X-ray diffraction （XRD）. The result shows that Ho^3＋ ,Tm^3＋ , and Yb^3＋ co-doped NaYF4 prepared by the hydrothermal method exhibits a hexagonal nanocrystal.

N-doped NaTaO3 synthesized from a hydrothermal method for photocatalytic water splitting under visible light irradiation

NaTaONcatalysts were synthesized by a hydrothermal（H） and a solid-state（S） methods in this study.The H-and S-NaTaONsamples were characterized by X-ray diffraction（XRD）, scanning electron microscopy（SEM）, transmission electron microscopy（TEM）, UV–visible（UV–vis） diffuse reflectance spectroscopy, and photoluminescence（PL） spectroscopy. The XRD patterns of the H-and S-samples showed peaks indexed to the pure phase of perovskite NaTaOand minor peaks assignable to TaNat various synthesis temperatures. Substitution of oxygen by nitrogen ions causes the light absorption of the H-and S-NaTaONsamples to be extended to the 600–650 nm region, thus making the samples visible-light active. The NaTaONsamples exhibited photocatalytic activity for Hand Oevolution from aqueous methanol and silver nitrate solutions under visible-light irradiation. The UV–vis and PL spectra of the Hand S-catalysts revealed the presence of cationic vacancies and reduced metallic species, which acted as recombination centers. These results demonstrated that the preparation method plays a critical role in the formation of defect states, thereby governing the photocatalytic activity of the NaTaONcatalysts.

Preparation of hydro-sodalite from fly ash using a hydrothermal method with a submolten salt system and study of the phase transition process

Hydro-sodalites are zeolitic materials with a wide variety of applications.Fly ash is an abundant industrial solid waste,rich in silicon and aluminum,from which hydro-sodalite can be synthesized.However,traditional hydrothermal synthesis methods are complex and cannot produce high-purity products.Therefore,there is a demand for processing routes to obtain high-purity hydro-sodalites.In the present study,high-purity hydro-sodalite(90.2 wt%)was prepared from fly ash by applying a hydrothermal method to a submolten salt system.Samples were characterized by powder X-ray diffraction(XRD),scanning electron microscopy(SEM),thermogravimetry and differential thermal analysis(TG–DTA),and Fourier transform infrared spectroscopy(FTIR)to confirm and quantify conversion of the raw material into the product phase.Purity of the samples prepared with an H2O/Na OH mass ratio of 1.5 and an H2O/fly ash mass ratio of 10 was calculated and the conversion process of the product phase was studied.Crystallinity of the product was influenced more by the Na OH concentration,less by the H2O/fly ash mass ratio.The main reaction process of the system is that the Si O ions produced by dissolution of the vitreous body in the fly ash and Na+ions in the solution reacted on the destroyed mullite skeleton to produce hydro-sodalite.This processing route could help mitigate processing difficulties,while producing high-purity hydro-sodalite from fly ash.

Synthesis of potassium hexatitanate whiskers using hydrothermal method

High quality potassium hexatitanate whiskers were hydrothermally synthesized in one step under moderate temperature and pressure conditions. Effects of the titanium source and reaction conditions on the hydrothermal reaction rate, product phase component, and morphology of whiskers were investigated. The results show that the reactivity of hydrated titania, anatase TiO2, and rutile TiO2 with KOH decreases in turn, and with hydrated titania as titanium source, it is difficult to obtain potassium hexatitanate whiskers with good morphology. In contrast, uniform potassium hexatitanate whiskers with a length of 10-20 μm and a diameter of 200-700 nm were obtained using anatase TiO2 as titanium source. The investigation demonstrates that the initial KOH concentration, annealing temperature and time, molar ratio of K2O/TiO2, etc. significantly affect the morphology of the as-synthesized whiskers. The optimized synthesis condition is as follows： anatase as a titanium source 10 wt.% KOH solution; annealing temperature and time of 300℃ and 5 h, respectively; K2O/TiO2 molar ratio of 5, etc. A rhombic potassium hexatitanate was prepared under the optimum condition and the whisker grew along the [110] direction. The reaction mechanism was discussed.

PREPARATION OF MULTI-WALLED CARBON NANOTUBES USING NiO CATALYST SYNTHESIZED BY HYDROTHERMAL METHOD

The Ni(OH)2/SiO2 binary colloid was prepared using Ni(NO3)2.6H2O and (C2H5O)4SiO4 as starting materials and was used to form NiO/SiO2. composite powder by hydrothermal method and desiccant method in open air respectively. Multi-walled carbon nanotubes (MWCNTs) were synthesized respectively by chemical vapor deposition using the NiO/SiO2 catalyst prepared by different methods. The phase and morphology of the catalysts and the morphology, output yield and purity of MWCNTs were compared by XRD, TEM and SEM. The results show that the catalyst powder prepared by hydrothermal method, compared with that by desiccant method, is smaller, better dispersion and has stronger catalytic activity. Pure MWCNTs with smaller tube diameter and narrow range could be obtained at a high yield using that NiO/SiO2 powder prepared by hydrothermal method as catalyst.

BIMORPH-TYPE PIEZOELECTRIC THIN FILM BENDING ACTUATORS SYNTHESIZED BY HYDROTHERMAL METHOD

Lead zirconate titanium solid-solution (PZT) thin films with variousthickness are synthesized on titanium substrates by repeated hydrothermal treatments. Young modulus,electric-field-induced displacement and the density of the PZT film are measured respectively.Bimorph- type bending actuators are fabricated using these films. The model, which is used toanalyze the driving ability of bimorph-type bending actuators by hydrothermal method, is set up. Itcan be seen that the driving ability of bimorph-type bending actuators can be greatly improved byoptimizing the thickness of PZT thin film and substrate from the theoretical analysis results. Themeasured values are expected to agree with the theoretical values calculated by the above model.

Upconversion Luminescence of YLiF_4∶Er^(3+) Synthesized by Hydrothermal Method

YLiF4： Er^3＋ was synthesized by hydrothermal method. Concentration of Er^3＋ is changed from 0 to 5 %. The absorption of Er^3＋ in all samples from 200 to 1200 nm was measured at room temperature. The J-O parameters calculated from absorption spectrum are Ω2： = 1.05 × 10^-20 cm^2, Ω4 = 1.25 × 10^-20 cm^2 and Ω6 = 1.35 × 10^-20 cm^2 Infrared-to-visible upconversion emission of YLiF4：Er^3＋ was observed when excited by 980 nm. The results show that the Er^3 ＋ content is less than 1.5 %, excite-state absorption is the main mechanism of upconversion emission. When Er^3＋ content is larger than 1.5%, both of the excite-state absorption and energy transfer lead to the upconversion luminescence. The upconversion intensity was enhanced with the increasing of Er^3＋ concentration. At room temperature, the lifetime of ^2H11/2 and ^4S3/2 is 205 μs while that of ^4F9/2 is 188 μs for sample Er-2. The transition rates and quantum efficiency were also calculated. The quantum efficiencies of ^4S3/2 and 4F9/2 are 27.9% and 10.7%, respectively.

Synthesis of Low-cost LiFePO_4 from Li_2CO_3 by a Novel Hydrothermal Method and Investigation on the Reaction Mechanism

Phspho-olivine Li Fe PO4 was synthesized from the relatively insoluble lithium source Li2CO3, proper iron and phosphorus sources（n（Li）：n（Fe）：n（P）=1：1：1） by a novel hydrothermal method. Afterwards, the optimal sample was mixed with glucose and two-step calcinated（500 ℃ and 750 ℃） under high-purity N2 to obtain the Li Fe PO4/C composite. The resultant samples were characterized by X-ray diffraction（XRD）, atomic absorption spectrometry（AAS）, scanning electron microscops（SEM）, transmission electron microscopy（TEM）, energy dispersive spectrometry（EDS）, elementary analysis（EA） and electrochemical tests. The results show that the optimal reaction condition is to set the reactant concentration at 0.5 mol·L^-1, the reaction temperature at 180 ℃ for 16 h duration. During the reaction course, an intermediate product NH4 Fe PO4·H2O was first synthesized, and then it reacted with Li＋ to form Li Fe PO4. The optimized Li Fe PO4 sample with an average particle size（300 to 500 nm） and regular morphology exhibits a relatively high discharge capacity of 84.95 m Ah· g^-1 at the first charge-discharge cycle（0.1C, 1C=170 m A·g^-1）. Moreover, the prepared Li Fe PO4/C composite shows a high discharge capacity of 154.3 m Ah·g^-1 at 0.1C and 128.2 m Ah·g^-1 even at 5C. Besides it has good reversibility and stability in CV test.

Preparation and electrochemical performance of nanosized Co_3O_4 via hydrothermal method

The hydrotalcite-type cobalt compounds were prepared through oxidation of Co(OH)2 gel using NH4OH as precipitating agent and H2O2 as oxidant. These hydrotalcite-type cobalt compounds were transformed into Co3O4 through hydrothermal decomposition with nanostructural deformation. The precursor and product were characterized by Fourier-transform infrared(FT-IR) spectrum, X-ray diffractometry(XRD) and transmission electron microscopy(TEM). The electrochemical performances of as-prepared nanosized Co3O4 as anode materials in lithium-ion batteries were tested by charge-discharge test in the voltage range of 0-3.0 V. The influence of morphology of Co3O4 particle on the capacity and cycling performance was studied. The results show that the shape and size of the final product can be controlled by altering cobalt sources. The irregular cubic Co3O4 with the average particle size of about 10 nm shows the best electrochemical performance. After 10 charge-discharge cycles, the specific charge capacity retains 555 mA·h/g.

Electronic microscopy analysis of HAP single crystals prepared by hydrothermal method

Hydroxyapatite(HAP, Ca 10(PO 4) 6(OH) 2) is one of the quite important bone implant materials. The hydroxyapatite crystals were synthesized under hydrothermal condition. The specimen was verified to be HAP crystal by the X-ray powder diffractometry(XRD). Then the specimen was distinguished single crystal from polycrystal by the use of the transmission electron microscope(TEM). The diffraction pattern of the specimen is neatly arranged diffraction spots, that verified the crystals were single crystals. The interplanar distance d calculated from diffraction spot is coincided with that of HAP’s JCPDS card. Moreover, crystal face angles calculated from crystal face index are coincided with the values by measuring on the pattern. The HAP crystals are needle-like in shape with about 3 μm in diameter and 180 μm in length. Most of the crystals are separate whiskers. Their length/diameter ratio ranges from 40 to 100. The average ratio is about 60.

Synthesis of mesoporous cerium-zirconium mixed oxides by hydrothermal templating method

Mesoporous cerium-zirconium mixed oxides were prepared by hydrothermal method using cetyl trimethyl ammonium bromide (CTAB) as template. The effects of amount of template, pH value of solution and hydrothermal temperature on mesostructure of samples were systematically investigated. The final products were characterized by XRD, TEM, FT-IR, and BET. The results indicate that all the cerium-zirconium mixed oxides present a meso-structure. At molar ratio of n(CTAB)/n((Ce)+(Zr))= 0.15, pH value of 9, and hydrothermal temperature of 120 ℃, the samples obtained possess a specific surface area of 207.9 m2/g with pore diameter of 3.70 nm and pore volume of 0.19 cm3/g.

Preparation of YVO_4:RE(RE=Yb^(3+)/Er^(3+),Yb^(3+)/Tm^(3+))nanoparticles viamicroemulsion-mediated hydrothermal method

A microemulsion-mediated hydrothermal method for synthesis of YVO4:RE(RE=Yb 3+/Er 3+,Yb 3+/Tm 3+)nanoparticles by hydrothermal treatment of quaternary microemulsion medium consisting of Na3VO4/NaOH and RE(NO3)3 aqueous solution, surfactant cetyltrimethylammonium bromide(CTAB),cosurfactant n-hexanol and oil phase n-heptane was report.The confinement of microemulsion droplets acting as microreactors during the reaction process allows the formation of small size YVO4:RE nanoparticles with relatively narrow size distribution and less aggregation.The structure,size and shape of YVO4:RE nanoparticles were investigated by means of X-ray diffractometry(XRD)and transmission electron microscopy(TEM).Compared with the conventional solid annealing diffusion method,the microemulsion-mediated hydrothermal method shows superiority in obtaining YVO4:RE nanoparticles with controllable size,narrow size distribution and less aggregation.The microemulsion-mediated hydrothermal method may be potentially applicable for synthesis of other rare earth doped up-converting luminescence nanomaterials.

K-Feldspar Decomposition Using CaO by Hydrothermal Method

The decomposition of K-Feldspar is significant to the development and utilization of K-feldspar as potassium resources. Potassium feldspar powder was decomposed successfully by hydrothermal method using CaO additive. Tobermorite solid and KOH solution were obtained as a result of the hydrothermal decomposition.

Preparation of Phosphogypsum-Based Calcium Sulfate Hemihydrate Whiskers by Hydrothermal Method

Calcium sulfate hemihydrate (CaSO4·0.5H2O, HH) is one of the three most commonly phases of gypsum observed in natural precipitates. Calcium sulfate hemihydrate whisker is a kind of fibriform single crystal with the mean diameter of 1-3 μm and the mean aspect ratio of 30–80. HH whisker was the most promising reinforcement seemed to be calcium sulfate-based due to its high intensity, high corrosion-resistance, good thermal stability, non-poisonous and low price. Thus, HH whiskers combine both reinforcement and low price, may be both effective in improving mechanical performance and extending application area.

Effects of La^(3+) doping on MnZn ferrite nanoscale particles synthesized by hydrothermal method

MnZn ferrite nanoscale particles were synthesized by hydrothermal method. The effects of amount of addition La3+ on the products were discussed. The product was characterized by X-ray diffraction （XRD） and transmission electron microscope （TEM）. The results show that the sample with 0.2% La3+（mass fraction） or without La3+ has only spinel phase, but the sample with mass fraction of La3+ exceeding 0.4% posses second phase besides the spinel one; and the nano-MnZn ferrites change from cube to hexagon when the mass fractions of La3+ is up to （1.2%.） TEM image of the sample with 1.2% La3+ indicates that the homogeneous hexagonal crystal is obtained and the particles are larger than those of undoped; the addition of La3+ has great influence on the crystallization of hydrothermal process and can change the shape of particles and improve their growth. The saturation magnetization of the sample with 1.2% La3+ (2.64 A·m2·kg-1) is lower than that of undoped (17.54 (A·m2·kg-1)) and it behaves superparamagnetically.

Studies on the Properties of ZnO Crystal Plane Grown by the Innovated Hydrothermal Method

ZnO single crystals were grown by the innovated hydrothermal method. The crystal surfaces were polished, and then studied by atom force microscope （AFM） and wet-chemical etching （WCE）. It was found that the Zn polar plane was smoother than O polar plane under the same polishing conditions. The etch pit density of Zn polar plane is 4.3×10^3 cm^-2, which is consistent with the previous report, while the density of etch pit of O polar plane is more than 103cm^-2. After annealing treatment, the density of etch pit of Zn plane reduces to 5.8×102 cm^2 and is superior to the current report. This investigation reveals that the high quality ZnO single crystals with fine Zn polar plane can be obtained by the innovated hydrothermal method.