Papers by Keyword: Hydrothermal

Abstract: This paper describes a simple two-step hydrothermal method for the design of heterojunction structure combined with TiO₂ nanorods coated with ZnO nanoparticles. TiO₂ nanorods on F-doped tin oxide (FTO) conducting glass are synthesized by hydrothermal method and ZnO coating is prepared through a two-step procedure. The XRD patterns confirm that the nanostructure consists of rutile TiO₂ and wurtzite ZnO without any other impure phase. The FE-SEM results show that ZnO is uniformly distributing on the surface of TiO₂ nanorods, forming a well-connecting heterojunction. PL studies and UV-vis absorption spectra present the enhanced optical performance of ZnO/TiO₂ heterojunction. The heterojunction structure ZnO/TiO₂ nanorods show excellent photoelectrochemical performance. The performance and the preparation parameters are also optimized accordingly.

Abstract: In generally, the metal catalyst which synthesis by conventional techniques is usually in metal oxide form or easily oxidize in the air thus the metal catalyst must reduce to metallic form before using. It was complex process and dangerous. In the research, Carbon material from cattail flower (CF) were used as supporter of Nickel/Carbon supported metal catalyst (Ni/C). This research were studied effect of used carbon material from CF as supporter of Ni/C and varying nickel loading. The Ni/C catalyst were prepared by hydrothermal, impregnation and calcination process. Firstly, Dried CF has been pretreat via hydrothermal process with optimized condition at 180°C for 8h. Then, the nickel solution was added to support via impregnation method by varying Ni loading from 20 to 60 wt% of supported. Finally, the sample has been pelleted into 0.5mm-Ni/C pellet and calcined at 900°C for 2h under nitrogen atmosphere. Ni/C were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), Energy dispersive X-ray (EDX), surface area and pore size distribution was determined by N2 adsorption. The result indicate that nickel particle on Ni/C were in the free metal from without reduction and well dispersed on supported surface. Particle size and surface area of Ni/C were decreases at the increase metal loading. Nickel/Carbon supported metal catalyst were ready to use and could be controlled particle size, surface area and crystallinity by metal loading.

Abstract: The conventional technique to synthesizes zeolite A from kaolin is calcination. However, this technique has one drawback since, the impurities in kaolin, such as muscovite and quartz, remain. Therefore, the hydrothermal process without calcination is used to synthesize high purity zeolite A. Hydrothermal synthesis without calcination can be separated into two steps, namely first and second hydrothermal steps. Alkaline activation reaction in the first hydrothermal step was used to study the effect of NaOH concentration ranging from 4M, 6M, 8M, 10M to 12M at 200°C for 3 hours. In this step, sodium aluminosilicate (cancrinite and nepheline hydrate) was produced and then dissolved in HCl. After filtration, the impurity was removed, and adjusted for neutral pH of 7 to form amorphous aluminosilicate gel. For the second hydrothermal step, amorphous gel was mixed with NaOH (1-4M) to form zeolite A at 90°C for 3 days. The x-ray diffraction (XRD) and Scanning Electron Microscope (SEM) were used for characterization.

Abstract: Synthesis of zeolite nanocrystals from rice husk ash and metakaolin was studied. Hydrothermal and solvothermal methods at 120 °C for 6 h were used as comparative study. Starting mixes were prepared with SiO₂/Al₂O₃ molar ratio of 4. Two factors; stirring time before hydrothermal and solvothermal treatments and solvent types were studied. The synthesized products were characterized in terms of mineralogy using X-ray diffraction, specific surface area using N₂ adsorption and desorption isotherm, morphology and composition using scanning electron microscopy and electron dispersion X-ray analysis. The results showed that faujasite and zeolite P1 were obtained from both of hydrothermal and solvothermal methods. However, crystals sizes of the synthesized zeolites from solvothermal method were smaller than that of hydrothermal method in that 100-300 nm and 100-1500 nm for solvothermal and hydrothermal methods, respectively. Specific surface area of the zeolites obtained from hydrothermal and solvothermal methods were 418 and 487 m²/g, respectively.

Abstract: Na (Y_1.5Na_0.5)F₆ microparticks were prepared by hydrothermal method. EDTA as the chelating agent. The samples were characterized by X-ray diffraction, scanning electron microscopy and fluorescence spectrometer. The X-ray diffraction indicates that the crystal shows a hexagon phase structure. Under the excitation of 980nm laser, the Na (Y_1.5Na_0.5)F₆ exhibited strong up-conversion light: ⁴F_9/2→⁴I_15/2(red), ⁴H_11/2/⁴S_3/2→⁴I_15/2(green) and ⁴G_11/2→²H_9/2 (near-ultraviolet).

Abstract: A hydrothermal processing technology was employed to synthesize Bi₄Ti₃O₁₂/TiO₂ composite by using TiO₂ and Bi(NO₃)₃ as reactor precursors, and KOH as mineralizer. The microstructure and composition of the as-synthesized samples were characterized by X-ray diffraction (XRD), scan electron microscopy (SEM), and the photocatalytic activity was studied. The results showed that Bi/Ti molar ratio, mass of the KOH and the hydrothermal parameters play important roles on the morphology and activities of the photocatalyst. We could obtain composites with good morphology and better performance with 200 °C hydrothermal treatment for 12 h, 0.01 mol/L of KOH, and 1:2 of mole ratio of Bi/Ti, as well as using good crystalline TiO₂ as the raw material. The as-prepared powder has a diameter of about 800nm, and the decolorized rate of methylene blue could reach 95 % after the UV-irradiation for 5 h.

Abstract: K_1-xNa_xNb_1-ySb_yO₃ lead-free piezoelectric ceramic powders were prepared by hydrothermal route. The samples were sintered under normal pressure at 1060 °C for 2 h. The structure of piezoelectric ceramics is perovskite and crystalline grain shows a block shape. With the different ceramics component and microstructure, piezoelectric constant d₃₃ varies from 20 to 73. When x=0.54, y=0.04, reached the maximum.

Abstract: Upconversion luminescence materials have been proved to have a good efficiency on converting low energy light to high energy light. These materials have received considerable attentions for many applications such as bio-labels, sensors, using for developing solar cells and photocatalytic applications under sunlight. Among many inorganic host materials, NaYF₄ has been proved to be the best for doping lanthanide ions and have a good upconversion emission due to its low phonon energy, chemical stability, and transparency in the near infrared to ultraviolet range. In this study, NaYF₄:Yb³⁺,Tm³⁺ upconversion luminescence materials were synthesized by hydrothermal method at temperature of 90 to 200 °C for period between 1 to 24 hours. The synthesized NaYF₄:Yb³⁺,Tm³⁺ were characterized by X-ray diffraction, scanning electron microscopy, and fluorescence spectroscopy. The hydrothermal temperature and reaction time have strongly influence on phases and upconversion emission of the synthesized NaYF₄:Yb³⁺,Tm³⁺. At 90 °C for 1 hour of reaction time, the pure cubic phase of NaYF₄:Yb³⁺,Tm³⁺ was found. After increasing temperature and reaction time, the NaYF₄:Yb³⁺,Tm³⁺ converted from cubic phase to hexagonal phase. Under excitation of 980 nm diode laser, the hexagonal NaYF₄:Yb³⁺,Tm³⁺ exhibited the emission wavelength at about 656 nm (³F₂ → ³H₆), 469, 492, 552 nm (¹G₄ → ³H₆), 537 nm (¹D₂ → ³H₅), 450, 461 nm (¹D₂ → ³F₄), 362 nm (¹D₂ → ³H₆) and 345 nm (¹I₆ → ³F₄). The upconversion emission intensity of the hexagonal NaYF₄:Yb³⁺,Tm³⁺ was much stronger, compared with that of the cubic NaYF₄:Yb³⁺,Tm³⁺.

Abstract: The nitrogen-doped mesoporous carbon spheres have been synthesized via soft-template and hydrothermal synthetic strategies using phenol/formaldehyde resins as carbon sources and melamine as a nitrogen source. The obtained carbon spheres exhibit a spherical morphology with a size range of 3-5 μm, which possess the narrow microporosity (ca. 1.2 nm) and mesoporosity (ca. 4 nm), large surface area (560-1200 m² g^-1) and high nitrogen contents (up to 15.7 wt%). Due to the well-developed porous structure and high nitrogen content, the carbon spheres show high performance for hydrogen storage, and the hydrogen adsorption capacities are in the range of 140-185 cm³ g^-1, which is better than that of most activated carbons. The incorporation of nitrogen into carbons is favored for hydrogen uptake in low pressure.

Abstract: This work describes the growth of 1-D Al-doped ZnO nanorods via low temperature hydrothermal reaction on seeded substrates. The amount of Al doped ZnO nanorods were tuned by using different concentration of aluminum nitrate from 1-20 mM. The optimum 5 mM Al doping produced an arrays of sharp-tip nanorods with average length of ~1.16 μm and average diameter of ~118 nm. I-V characteristic of the Al-doped ZnO nanorods fabricated onto Al electrodes were observed under UV illumination and dark condition. The change in photoconductivity of Al-doped ZnO nanorods under UV light was found two orders of times higher compared to ZnO nanorods. Different concentrations of aluminium doped ZnO nanorods UV sensing showed response to UV light but with different sensing value. 5 mM Al-doped ZnO showed high responsivity of fabricated UV sensing at 3V with 23.56 A/W which was higher compared to other concentrations. This suggested that the responsivity of Al-doped ZnO NRs UV sensing could be controlled to some extent by controlling the percentage of Al-doped.