Papers by Keyword: Hydrothermal Synthesis

Abstract: TiO₂ (B) nanowires were prepared at 170 °C, 200 °C and 220 °C for 24 h via hydrothermal synthesis to evaluate the effect of temperature on phase composition and morphologies. The effect of reaction time: 24 and 72 h on the formation was also studied at 170 °C. All samples were calcined in air at 400 °C for 2 h. Phase identification was performed using X-ray diffraction (XRD) and morphologies was examined by a scanning electron microscope (SEM). It was found that hydrothermal temperature and time played an important role in defining TiO₂ phase composition and its morphology. For 24 h hydrothermal synthesis, at low temperature of 170 °C, anatase TiO₂ nanoparticles were formed, while at higher temperature of 200 and 220 °C, TiO₂ (B) nanowires with averaged diameter of 49 nm and several micrometers in length were produced. Interestingly at 170 °C, by increasing reaction time to 72 h, anatase TiO₂ nanoparticles were completely transformed to TiO₂ (B) nanowires with averaged diameter of 74 nm and 2-4 micrometers in length.

Abstract: In this work, BaTiO₃ nanoparticles were synthesized through hydrothermal method. The powder obtained from the hydrothermal process (as-synthesized powder) was calcined at 1000 °C. The phase formation and morphology of the as-synthesized and calcined powders were studied using X-ray diffraction (XRD), thermogravimetric (TGA) and differential scanning calorimetry (DSC) analyzer, and transmission electron microscope (TEM). The XRD data showed that the as-synthesized powder is partially amorphous. Upon calcining the powder at 1000 °C, highly crystalline BaTiO₃ with tetragonal structure was obtained. As shown by TGA and DSC analysis, the precursor powder was completely transformed into BaTiO₃ at 1000 °C. The presence of BaCO₃ as an impurity phase in the powder is due to the lack of Ba²⁺ / Ti^3+/4+. Transmission electron microscope images showed that the particle size of the as-synthesized powder increased after calcination due to crystal growth. In addition, nanocubes with the average size of around 11.66 nm were obtained as a result of the calcination compared to the ellipsoid like particles of the as-synthesized powder.

Abstract: Supercritical hydrothermal synthesis is a green synthesis method for metal and metal oxide ultra-fine particles. Ultra-fine copper particles are of great interests for the researchers because of the excellent performance in recent years. In this paper, supercritical hydrothermal synthesis of copper ultra-fine particles with three different precursors (CuSO₄, Cu(NO₃)₂, Cu(HCOO)₂) are reported. This thesis reports that different products are produced with different precursors. Also, three kinds of reaction mechanisms with different precursors in supercritical water were explained. The conversion of copper ions in the reaction of Cu(HCOO)₂ in supercritical water is the highest, the value reaches 100.0%. In the process of synthesizing ultra-fine copper particles, different additional HCOOH concentrations (0, 0.1 mol/L, 0.2 mol/L) and different reaction times (5 mins, 10 mins) were applied. Zero-valent ultra-fine copper particles without impurity were synthesized. The synthesized copper ultra-fine particles were cubic aggregations with micro-meter size

Abstract: Zeolites are crystalline microporous aluminosilicate of alkali metals and alkaline-earth metals. These materials have large commercial application due to their physical and chemical properties. The synthesis of zeolite A was carried out based on procedures described by International Zeolite Association (IZA), the sodium silicate was used as a source of silicon and the sodium aluminate as a source of aluminum for the produced zeolite. The synthesis occurred at hydrothermal conditions through static autoclaving. The material formed was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The results obtained from the characterization analysis were satisfactory and the method of synthesis showed to have high reproducibility in the production of zeolite A with good crystallinity as predominant phase. This result is very interesting because this method is simple and did not use toxic organic compounds as templates.

Abstract: Monodisperse nanoparticles are materials that are not agglomerate. The good characteristic of these materials is the dispersity in water, so they can better react with target pollutants. Accordingly, in this work, the monodisperse magnetite nanoparticles with the superparamagnetic property were synthesized and characterized. The hydrothermal method with the iron compound and polymer as precursors was conducted. The magnetic nanoparticles were characterized by several techniques including X-ray diffraction, field emission scanning electron microscope, transmission electron microscope, and vibrating sample magnetometer. The saturation magnetization (Ms) value, the coercivity (Hc), and the retentivity (Mr) were measured to demonstrate the paramagnetic behavior of the monodisperse magnetite nanoparticles. The results showed that the Fe₃O₄ nanoparticle were obtained at 200 °C for 16 h. The particles are monodispersed with the size approximately in the range of 60 - 250 nm as confirmed by FE-SEM and TEM images. These are the single grain and had the spherical shape similar to a blackberry. The saturation magnetization of 17.287 emu/g and ratio of retentivity to saturation magnetization (Mr/Ms) characterized the squareness of the hysteresis loops was 0.03653. It can be indicated that the Fe₃O₄ nanoparticles had superparamagnetic behavior. This property of Fe₃O₄ nanoparticles can draw pollutants to absorb on the surface of these nanomaterials. Then adsorbed pollutants can be easily removed by separating the Fe₃O₄ materials from water. This technique can be applied further in water treatment and pollutant removal.

Abstract: Spherical Sm₂O₃ nanoparticles have been successfully synthesized by microwave-assisted hydrothermal technique in the condition of different microwave radiation power. The microstructure, morphology and optical properties of the samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), field emission transmission electron microscope (FETEM) and ultraviolet-visible (UV-vis) spectrophotometry. The results showed that the precursors Sm (OH)₃ nanorods and SmOHCO₃ nanoparticles were obtained during microwave-assisted hydrothermal reaction and decomposed into spherical Sm₂O₃ nanoparticles after heat treatment. A potential mechanism of the formation of Sm₂O₃ nanoparticles is proposed. The UV-vis absorption spectra indicated that the samples had high ultraviolet absorption capacity and the energy gap was only 4.83 eV as the radiation power increased to 550 W.

Abstract: Abstract. ZnO nanoparticles with different morphology were synthesized through a one-step and low temperature hydrothermal method with different reaction time. The prepared ZnO nanoparticles have been used as photocatalysts for the degradation of methylene blue (MB) aqueous solution under UV irradiation to study the relationship between the morphology and photocatalytic performance. The phase, crystallographic structure and morphology of synthesised ZnO nanoparticles were characterized by scanning electron microscope (SEM) and X-ray diffraction (XRD). The photocatalytic activity of ZnO nanoparticles were carried out by UV-visible spectroscopy (UV-vis). SEM results showed that different particle sizes and morphologies of flower-like, elliptical-shape and rod-shapes were obtained at 60 °C for 1 h, 4 h, 8 h and 12 h, which promoted photodegradation of methylene blue (MB) aqueous solution under UV light irradiation. Especially, elliptical-shape ZnOnanoparticles with reaction time of 4 h were most efficient, and the degradation rate was up to 98.2% after 20 min UV irradiation.

Abstract: The addition of certain co-solvents to the hydrothermal synthesis starting solution can greatly alter morphology and enhance different morphology dependent properties of the synthesized material. While ethanol is the most common co-solvent used for the synthesis of various SnO₂ nano/microstructures by hydro/solvothermal process, it is not clear how the use of some other alcoholic co-solvents (for example, methanol or isopropanol) affect morphology and properties of SnO₂, especially if synthesis is done under similar conditions as in the case of ethanol co-solvent. In the present study, we investigated how the use of various alcoholic co-solvents (methanol, ethanol, 2-propanol, ethylene glycol and glycerol) affects crystal structure, morphology and specific surface area of the hydrothermally synthesized SnO₂. Additionally, sensitivity towards 100 ppm ethanol of the synthesized materials was tested. The formation of nanoparticles, rod-cluster structures and spherical SnO₂ structures were observed depending on the alcoholic co-solvent used. The highest sensitivity (~22 at 250 °C) showed the material that was synthesized in the presence of ethanol co-solvent.

Abstract: Nickel oxide (NiO) was prepared by the hydrothermal method using hydrogen peroxide to form a nickel peroxide complex, and irregular spherical and rod-shaped NiO nanoparticles were obtained. The factors that influence the physical properties of NiO nanoparticles were studied using scanning electron microscopy (SEM), isothermal gas adsorption/desorption by Brunauer, Emmett and Teller (BET), and X-ray diffraction (XRD) techniques. This study found that the precursor salt chosen (nickel acetate or nickel nitrate) significantly affected the shape, particle size, and surface area of the synthesized nanosized NiO powders. The ratio of hydrogen peroxide (H₂O₂) to nickel nitrate or acetate and the heating rate of calcinations were also important in determining the physical properties of the nanosized NiO. The unmodified PAni electrode shows no activity for the methanol oxidation reaction in 0.1 M NaOH. However, the nickel-modified PAni electrode is a good catalyst for this reaction and high current densities can be reached. The height of the oxidation peak of methanol increases by increasing the alcohol concentration. The results indicate that the reaction of the electro-oxidation of methanol is an activation-controlled proceeding by a direct chemical reaction with NiO(OH) for thin nickel oxides and by charge transfer with the electrode for thick oxides.

Abstract: The surface structure of Hydroxyapatite (HAp) particles during hydrothermal synthesis and their protein adsorption behavior was investigated. The HAp particles were prepared by mixing calcium acetate solution and diammonium hydrogen phosphate solution by hydrothermal synthesis. When the temperature of mixture were heated up to 120°C, 150°C and 180°C, the HAp particles were collected during hydrothermal synthesis. The adsorption properties of proteins onto HAp were studied using three types of proteins: bovine serum albumin (BSA), myoglobin (MGB) and lysozyme (LSZ). Surface analysis by BET revealed that their pore volumes were decreased by increasing synthesis temperature. The adsorbed amount of BSA and LSZ per unit milligrams showed no obvious difference in all of the HAp particles prepared with synthesis temperature. In contrast, the amount of MGB adsorbed onto HAp particles synthesized at 120°C, 150°, and 180°C shows the decreasing with an increasing synthesis temperature. This result suggests that the adsorbed amount of MGB was decreased by decreasing pore volume of HAp particles.