Papers by Keyword: Hydrothermal Synthesis

Abstract: The barium ferrite BaFe₁₂O₁₉ with c-plane anisotropy, which possessed relative high saturation magnetization and low coercivity, had been synthesized by hydrothermal method with different reaction time of 5 h, 8 h,11 h,14 h, and 17 h. The X-ray diffraction (XRD), field emission scanning electron microscope (FESEM) and vibrating sample magnetometer (VSM) were used to study the phase composition, microstructure and magnetic properties of barium ferrite, respectively. The results showed the intensities of the peak were enhanced and there was no impurity phase. With the prolonging of the reaction time to 11 h, 14 h and 17 h, the grain size increased, and the equivalent diameter was about 1 μm, and the thickness was about 100 nm. When the reaction time was 17 h，the coercivity of barium ferrite was 1104 Oe. The reduction of coercivity was ascribed to the increase of particle size and the reduction in magnetic anisotropy.

Abstract: The conditions for the synthesis of aluminum tungstate Al₂(WO₄)₃ and aluminum niobate AlNbO₄ were clarified using hydrothermal treatment and post-heating. Single-phase Al₂(WO₄)₃ can be synthesized through the hydrothermal treatment of the starting materials at a mixing ratio of Al:W = 5:5 at 250 °C for 5 h and post-heating at 840 °C for 6 h. The AlNbO₄ was synthesized using the same method, under a hydrothermal treatment of Al:Nb = 2:8 and post-heating. As a result of investigating the products under various mixing conditions based on the synthesis of pure Al₂(WO₄)₃ and AlNbO₄, Nb could not be doped into Al₂(WO₄)₃, but W-doped AlNbO₄ was synthesized. The electric conductivity was measured for several samples of sintered W-doped AlNbO₄, and the results showed that the electrical conductivity was improved within a higher temperature region by doping with W.

Abstract: In this work it was investigated the influence of CTAB surfactant concentration on the synthesis of the compound Mn_0.75Zn_0.25Fe₂O₄ by the coprecipitation method. It was also compared the influence of hydrothermal treatment on the synthesized materials. The magnetic properties were characterized by AC susceptometry for the determination of the magnetic susceptibility and magnetic density energy. The phases, crystal structure and morphology of the nanoferrites were determined by Rietveld analysis of X-ray diffraction data. It was found the presence of two phases: Franklinite and Akaganeite and it was shown that the samples synthesized only by coprecipitation presented the tendency to increasing the crystallite sizes of the akaganeite phase and decreasing of crystallite sizes of the Franklinite phase as a function of CTAB concentration. The samples submitted to subsequent hydrothermal treatment presented a tendency to decreasing the crystallite sizes of both phases and increasing in Franklinite phase fraction, compared to the samples synthesized only by coprecipitation, suggesting that the hydrothermal treatment was effective in obtaining nanostructured materials of smaller particles.

Abstract: Improving the hydration hardening building materials’ operational properties is possible due to the stable macro-, micro-and nanostructures’ creation by the cementing material crystalline aggregate directed modification, which can be achieved through the use of various additives acting as crystallization centers. In the course of the studies, the synthesized modifier effect nature represented by the system was revealed CaO-SiO₂-H₂O (CSH) on the properties of non-autoclave silicate materials using aluminosilicate binder of various compositions. It has been established that the use of an aluminosilicate binder together with the addition of a CSH modifier increases the presence of a crystalline phase at all stages of hardening, as well as intensifies the synthesis of low-basic calcium hydro silicates with a higher crystallization degree in the system CaO-SiO₂(Al₂O₃)-H₂O represented by lime and clay rocks. This contributes to the micro-reinforced crystalline framework formation of the neoplasms with increased strength. Due to this, the pore space decreases and the amount of synthesized crystalline substance increases, which helps to increase the water resistance of the samples in all compositions. The samples using an aluminosilicate binder and the addition of a CSH modifier achieve maximum strength with a CaO content of not more than 10 wt. % The optimal CSH modifier addition is up to 1.5 wt. %, with 7 wt. %, CaO content in a mixture increase in strength is up to 6%.

Abstract: The crystal morphology and geometry may play a role in electronic dissemination transition, and they would lay the foundation for the assembly about various accessories. The main aim of our research is to investigate a variety of factors which had an impact on the types and morphologies of the final products during the Co(OH)₂ crystal formation process, such as substrate material, reaction concentration and reaction time. In this paper, Co(OH)₂ microspheres are successfully prepared by a facile hydrothermal synthesis method, using cobalt nitrate hexahydrate and ammonium fluoride as the raw material, ammonia as the complexing agent and a clean nickel or copper foam as the base material. The structure and morphology of samples are characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM).

Abstract: A hydrothermal method using tetrabutyl titanate and KOH as reactants for synthesis of K₂Ti₆O₁₃ nanowires was developed, obtaining nanowires with a uniform diameter around 10nm. It is shown that the hydrothermal temperature and the KOH concentration have little influence in tuning the growth of K₂Ti₆O₁₃ nanowires. By changing the time for hydrothermal reaction, the length of K₂Ti₆O₁₃ nanowires can be controlled from several dozen of nanometers to several hundreds of nanometers. The as-prepared K₂Ti₆O₁₃ nanowires exhibit a wide and strong absorption band in the ultraviolet range (around 200~300 nm), and stable photocurrent of 0.5μA/cm², which might suggest potential applications in solar cell and water splitting.

Abstract: In response to global energy and environmental issues, development of efficient and robust earth-abundant electrocatalysts for hydrogen evolution reaction is particularly meaningful. In this study, a facile hydrothermal method is developed to synthesize porous CoS₂ nanostructures by using sulfur powder and thiourea as sulfur sources on carbon cloths for highly efficient hydrogen evolution reactions. The huge load of CoS₂ on carbon cloth，their unique porous nanostructures equiped CoS₂ nanomaterials with excellent electrocatalytic properties. The remarkable HER catalytic performance was achieved with -67 mV at a current density -10 mA cm^-2 and the Tafel slope 62 mV dec^-1 in 0.5 M H₂SO₄ solution. The overpotential of HER only lost 2 mV after 1000 cycles with remarkable stability. I think this work opens up a low cost and scalable route to fabricate transition metal-based materials for application in electrocatalysis.

Abstract: Titanium dioxide (B phase) with 1-D structures was successfully fabricated via a hydrothermal method with a subsequent ion-exchange process and calcination. P25, titanium isopropoxide (TTIP), rutile and also anatase were used as Ti precursors in the alkali hydrothermal system. TTIP promoted an elongation of nanorod morphology whereas the other precursors produced short nanorod structures. The different types of titanium precursors did not have any influence on the phase transformation during the fabrication process. Na₂Ti₆O₁₃ was the primary intermediate product after washing the hydrothermal sample. H₂Ti₃O₇ was the secondary intermediate phase obtained following proton-exchange of Na₂Ti₆O₁₃ in HNO₃ solution. Finally, the TiO₂(B) phase was the product of calcination of the secondary intermediate product at 400°C for 5 hr. A phase transformation mechanism is presented based on an investigation of products at each of the steps. The effects of the synthesis conditions on tailoring of the crystal morphology are discussed. The growth direction of the TiO₂(B) nanorods was investigated by HR-TEM and SADP. Finally, the metastable phase of TiO₂(B) was shown to be transformed to anatase during thermal treatment at temperatures higher than 400°C.

Abstract: Bismuth vanadate (BiVO₄ ) powders were synthesized using Bi (NO₃)₃.5H₂O and NH₄VO₃ as raw materials, NaOH and HNO₃ for pH adjustment. The samples were characterized by X-ray diffraction ( XRD ), scanning electron microscopy (SEM ) and UV-vis diffuse reflectance spectra techniques. The results show that the pH of precursor solution has great effect on the composition and morphology of products. Synthetic product was BiVO₄ with two kinds of crystal shape ( monoclinic and tetragonal ) with pH of 3; synthetic product was pure monoclinic phase BiVO₄ when the pH is between 5-9. Whereas, V₂O₅ and Bi₂O₃ appeared when the pH was 11; synthetic product was a mixture of V₂O₅ and Bi₂O₃ with pH of 13, and BiVO₄ don’t exist. The photocatalytic activity was evaluated by the degradation of methylene blue solution. It is shown that the synthetic sample has the best photocatalytic ability with pH of 5. The degradation of methylene blue reaches 84.7% when irradiated for 240 min by high pressure mercury lamp, and the sample synthesized at 13 for pH has strong adsorption capacity and poor photocatalytic ability.

Abstract: Fe₃O₄@C spheres were synthesized by hydrothermal reaction at 190°C followed by a low temperature heat annealing at 600 °C and applied as an anode material for lithium-ion batteries. The samples were characterized by XRD and SEM. The electrochemical performances of as-synthesized Fe₃O₄@C were systemically investigated. A reversible capacity of 873 mAh g^-1 is obtained in the second cycle at 400 mA g^-1. More importantly, the discharge specific capacity can still maintain at about 767 mAh g^-1 after 80 cycles. Moreover, Fe₃O₄@C spheres electrode shows satisfactory rate capability even at a rate up to 2000 mA g^-1. Thus, the results demonstrate that Fe₃O₄@C spheres show encouraging application potential to be an advanced anode material for lithium storage