Hydrothermal synthesis of single-crystalline anatase TiO2 nanorods with nanotubes as the precursor

Preparation of anatase TiO2 nanorods from solutions in the absence of surfactants or templates has rarely been reported. The present work has found that hydrothermal treatment of titanate nanotube suspensions under an acidic environment resulted in the formation of single-crystalline anatase nanorods with a specific crystal-elongation direction. The nanotube suspensions were prepared by treatment of TiO2 in NaOH, followed by mixing with HNO3 to different pH values. The crystal size of the anatase nanoparticles obtained from the hydrothermal treatment increased with the pH of the suspensions, and nanorods with an aspect ratio up to 6 and a long axis along the anatase [001] were obtained at a pH slightly less than 7. A mechanism for the tube-to-rod transformation has been proposed on the basis of the crystalline structures of the tubes and rods. The local shrinkage of the tube walls to form anatase crystallites and the subsequent oriented attachment of the crystallites have been suggested to be the key steps involved in the nanorod formation.     

Hydrothermal synthesis of potassium titanate nanotubes doped with magnesium,nickel, and aluminum

Study of the phase formation in the systems TiO₂?MO(M₂O₃)?KOH?H₂O (M = Mg, Ni, Al) from crystalline and coprecipitated X-ray-amorphous mixtures demonstrated that doped potassium titanate nanotubes can be obtained in a hydrothermal treatment of coprecipitated hydroxides in the temperature range 170?220°C. The average outer diameter of the thus synthesized nanotubes strongly depends on the element being introduced and is 5 to 10 nm. The nanotubes have a large specific surface area (200?300 m2 g?1) and are stable up to a temperature of 500°C, above which they decompose to give potassium hexatitanate. The nanotubes can be used as sorbents, photocatalysts, and components of composite materials for frictional and construction purposes.     

Hydrothermal synthesis of prismatic NaHoF(4) microtubes and NaSmF(4) nanotubes

A new example of tubular materials based on sodium rare-earth tetrafluorides, NaHoF(4) and NaSmF(4), has been fabricated by a simple hydrothermal method. In addition, an unusual nanotube with a perfect couple of an outer prismatic shell with an inner concentric prismatic nanorod at the center is found. According to the architectures of various products, the general growth mechanism of these tubes is proposed.     

Hydrothermal synthesis of two perovskite rare-earth manganites, HoMnO3 and DyMnO3

Two perovskite rare-earth manganites RMnO₃ (R=Ho, Dy) were synthesized from the hydrothermal redox reactions of KMnO₄ and MnCl₂ at 250 °C and characterized by means of X-ray diffraction, scanning electron microscopy and SQUID. They are orthorhombic, whereas the hexagonal phases, which were competitive strongly with the orthorhombic phases in solid-state reactions, are avoided in the hydrothermal systems. The pure metastable manganites may serve as a model for understanding the magnetisms of Jahn-Teller distortion and charge ordering. This new synthetic approach leaves many rooms for new doped or undoped RMnO₃ compounds.     

Large-scale synthesis of single-crystalline perovskite nanostructures

Single-crystalline perovskite nanostructures with reproducible shape have been prepared using a simple, readily scaleable solid-state reaction in the presence of NaCl and a nonionic surfactant. Pristine BaTiO3 nanowires have diameters ranging from 50 to 80 nm with an aspect ratio larger than 25. Single-crystalline SrTiO3 nanocubes with a mean edge length of 80 nm have been produced using a similar procedure.     

利用水热法制备氧化锌微米球

利用水热法制备出具有特殊形貌的ZnO微米球.利用X射线粉末衍射仪(XRD)和扫描电镜(SEM)对ZnO进行了表征.     

Hydrothermal synthesis of rare-earth fluoride nanocrystals

In this paper, a hydrothermal synthetic route has been developed to prepare a class of rare-earth fluoride nanocrystals, which have shown gradual changes in growth modes with decreasing ionic radii and may serve as a model system for studying the underlying principle in the controlled growth of rare-earth nanocrystals. Furthermore, we demonstrate the functionalization of these nanocrystals by means of doping, which have shown visible-to-the-naked-eye green up-conversion emissions and may find application in biological labeling fields.     

Hydrothermal synthesis of nanotubular Mg-Fe hydrosilicate

Magnesium iron hydrosilicate nanotubes with a chrysotile ((Mg,Fe)₃Si₂O₅(OH)₄) structure have been synthesized hydrothermally at t = 250–450°C and p = 30–100 MPa. In the hydrothermal synthesis of (Mg,Fe)₃Si₂O₅(OH)₄ chrysotile, part of the Fe²⁺ ions oxidize to Fe³⁺ and are incorporated into the octahedron and tetrahedron layers of the chrysotile structure. The limiting iron content of chrysotile has been determined up to which cylindrically rolled layers can form to yield nanotubes. The hydrothermal treatment of precursors richer in FeO yields platelike hydrosilicates. The iron ions present in the starting components affect the synthesis parameters, morphology, size, optical properties, and thermal stability of the nanotubes.     

溶剂热合成碳纳米管

自1991年Iijima发现碳纳米管以来,碳纳米管因其独特的结构和物理化学性质而成为人们的研究热点。     

Sonoelectrochemical synthesis of CdSe nanotubes

CdSe nanotubes were successfully synthesized by a sonoelectrochemical technique for the first time; the formation process of the CdSe nanotubes was carefully studied and a sonication-induced roll-up mechanism is proposed.     

Combustion synthesis and characterization of porous perovskite catalysts

Porous perovskite-type complex oxides LaCoO₃ and La_0·95Sr_0·05Ni_0·05Co_0·95O₃ were produced by combustion method. The properties of these porous materials such as crystal structures, particle sizes, surface patterns, pore size, surface area and pore volume were characterized by X-ray diffraction( XRD), scanning electron microscopy(SEM) and BET measurements. The results indicated that all porous materials are of the perovskite-type complex oxides. Doping Sr²⁺ ions on site A and doping Ni²⁺ ions on site B entered the crystal lattices of LaCoO₃ in the place of La³⁺ and Co³⁺, respectively, and the maximum peak of XRD patterns of doping sample was weaken and broaden. Morphological microscopy demonstrated agglomerates involved mostly thin smooth flakes and layers perforated by a large number of pores and its lamella decreased with the introduction of Sr²⁺ and Ni²⁺. Hysteresis loop in the N₂ adsorption-desorption isotherm of samples indicated its porous structures and the doping effect on its pore size, surface area and pore volume were improved. The porous catalysts have been tested for methane catalytic combustion and the results showed that these catalysts possessed high catalytic activity.     

Hydrothermal synthesis of single-crystalline antimony telluride nanobelts

The single-crystalline Sb2Te3 nanobelts were successfully synthesized by a novel and convenient surfactant-assisted hydrothermal approach. The ionic surfactant AOT acted as the shape controller in the synthetic process. We believe that this synthetic route could be applied to obtain other low-dimensional semiconducting telluride nanostructures.     

Hydrothermal synthesis of porous materials from sepiolite

In order not only to manufacture a tough porous material from sepiolite but also to sustain the inherent properties of the sepiolite, a hydrothermal experiment was carried out under saturated steam pressure at 473 K for up to 24 h by mixing slaked lime. The experimental results show that the addition of slaked lime exerts a positive effect on the strength development, and the strength enhancement is found to be due to tobermorite and calcium silicate hydrate (CSH) gel formation. Curing time seems to condition the strength development. A fine particle size of sepiolite improves its activity during the hydrothermal process, thus offering a higher strength and quicker hardening rate of the synthesized specimen. The acid activation also has a beneficial effect on the strength development. The hardening mechanism of the synthesized specimen is different between the specimens synthesized with or without acid activation. The strength enhancement for sepiolite with acid activating is due mainly to CSH gel formation, instead of tobermorite formation without acid activation.     

Hydrothermal synthesis of tungsten molybdenum mixed oxides

The phase composition, particle size, and morphology of ultrafine products recovered as a result of hydrothermal treatment of precursor solutions were studied. The precursor solutions were prepared by ion exchange and contained various proportions of tungsten and molybdenum. When tungsten percentages in the precursor solution were 20–95 mol %, the major synthesis product was a mixed oxide (substitutional solid solution (W, Mo)O₃ · 1/3H₂O based on the structure of crystal hydrate WO₃ · 1/3H₂O). When the tungsten percentage was 5 mol %, the product was (W, Mo)O₃ solid solution with the structure of orthorhombic MoO₃. Particle shapes and sizes (ranging from 20 to 8 000 nm) were dictated by the proportion between tungsten and molybdenum compounds in the precursor solution and by the method used to prepare the precursor.     

Hydrothermal synthesis of lithium iron phosphate cathodes

Hydrothermal methods have been successfully applied to the synthesis of lithium iron phosphates. Li₃Fe₂(PO₄)₃ was synthesized by heating at 700°C LiFePO₄(OH), formed hydrothermally in an oxidizing environment. Crystalline LiFePO₄ was formed in a direct hydrothermal reaction in just a few hours, and no impurities were detected. This result leads to the possibility of an easy scale-up to a commercial process. The samples were characterized by X-ray diffraction, thermogravimetric analysis and scanning electron microscopy. Both phosphates were tested as the cathode in lithium batteries and showed results comparable to those formed by conventional high-temperature synthesis.     

Hydrothermal synthesis of crystalline rectangular titanoniobate particles

Potassium titanoniobate (KTiNbO5) crystalline powders possessing rectangular particle shapes and large surface areas which are prerequisite for high photocatalytic performance have been successfully synthesized by a novel hydrothermal method.     

Hydrothermal synthesis of cadmium sulfoselenide inclusion pigment

In this communication, a hydrothermal method for synthesizing cadmium sulfoselenide inclusion pigment was introduced. The general synthesis procedure was as follows: (1) the hydrothermal preparation of CdS _x Se_(1−x)-CeO₂ nanoparticles; (2) the dispersion of the CdS _x Se_(1−x)-CeO₂ nanoparticles in a prehydrolyzed TEOS; (3) the formation of a CdS _x Se_(1−x)-CeO₂-SiO₂ nano-composite by the gelation of the prehydrolyzed TEOS; (4) the inclusion of the CdS _x Se_(1−x) into the SiO₂-CeO₂ matrices by a hydrothermal treatment. The crystalline phase, thermal effect, microstructure and L*a*b* color parameters of the pigment were investigated by X-ray diffraction (XRD), a Differential Scanning Calorimeter (DSC-TG), a transmission electron microscope (TEM) and a differential colorimeter. The results showed that CdS _x Se_(1−x) could be partially stabilized to more than 1100 °C by the hydrothermally-densified CeO₂-SiO₂ glassy phase. The inclusion pigment showed a stable red color at 1100 °C, though it was not bright red.