Simple Solvothermal Technique Research Articles

Solvothermal Processing of Amorphous TiO2 Nanotube Arrays: Achieving Crystallinity at a Lower Thermal Budget

Highly aligned, vertically oriented TiO2 nanotube arrays formed by electrochemical anodization have been extensively investigated in the recent times because of various potential applications such as in solar cells, hydrogen generation, CO2 reduction, gas sensors and as biocompatible material. The as prepared nanotubes, however, are amorphous and require a thermal annealing process to achieve the desired crystallographic phase. Here we report a simple solvothermal technique by which the crystallinity of the nanotube arrays can be tailored at temperatures around 200 °C to achieve the anatase phase without destroying the tubular morphology. In this alcohol-based solvothermal process, the crystallinity can be enhanced by changing the solvent from methanol to isobutanol and the sample treated with isobutanol for 2 h shows crystallinity and strain comparable to that of a sample annealed in a conventional furnace at 550 °C. A mechanism for the solvothermal crystallization and the enhancement of crystallinity ha...

Solvothermal Synthesis of Nitrogen-Containing Graphene for Electrochemical Oxygen Reduction in Acid Media

Graphene is ideally suited to electrochemistry by virtue of its high surface area and impressive electronic properties. Nitrogen incorporation can be used to tailor the properties of graphene. Here we present a simple solvothermal technique to produce a nitrogen-containing foam-like macroporous graphene powder doped with up to 15 wt% nitrogen. This is applied as an effective non-precious, metal-free electrochemical catalyst for oxygen reduction in acid media. [DOI: 10.1380/ejssnt.2012.29]

Controlling the morphology and size of CuO nanostructures with synthesis by solvo/hydrothermal method without any additives

CuO nanostructures at different morphologies were synthesized in controlled manner using a simple low-temperature solvothermal technique. Controlling the pH of content the reaction mixture, nanoparticles, nanorods and nanocloud CuO structures were synthesized at temperature of 100–150 °C with excellent reproducibility. High-resolution electron microscopy revealed the well crystalline nature of all the nanostructures with preferential growth along the [0 0 2] direction for linear structures. Photoluminescence spectrum of the as-grown nanostructures revealed oxygen-vacancy-related defects in them. The average sizes of NP-CuO (nanoparticles of CuO) at different morphologies were between 40 and 100 nm. The structure, morphology and size of NP-CuO were determined by X-ray diffraction powder (XRD), scanning electron microscopy (SEM), solid state Photo Luminescent (PL) and EDAX analysis.

Water repellent ZnO nanowire arrays synthesized by simple solvothermal technique

The authors report on the water repellent properties of quasialigned zinc oxide (ZnO) nanowire arrays grown by low-temperature solvothermal technique. The uniform and dense ZnO nanowires of average diameter ∼ 75 nm have been found to have hexagonal wurtzite type structure. The as synthesized ZnO nanowire surfaces have hydrophilic nature with a water contact angle of 73° ± 3°. The superhydrophobic behavior with a water contact angle of 145° ± 3° of the nanowire arrays has been realized due to the reduction of surface free energy after being coated with an octadecyltrichlorosilane (OTS) monolayer. This work may be of huge importance from the viewpoint of both the understanding of the mechanisms involved and industrial applications.

Synthesis and characterization of In 2O 3 nanocube via a solvothermal-calcination route

In 2O 3 nanocubes have been generated by a two-step process, a simple solvothermal technique for In(OH) 3 nanocubes and subsequent reaction with O 2 to form the In 2O 3 nanocubes, which exhibit morphologies identical to the original In(OH) 3 nanocube. The In(OH) 3 nanocubes and the In 2O 3 nanocubes are well-crystallized single-crystal nanostructure. Under optimal conversion conditions, the final geometry features of In 2O 3 are predetermined by the size and morphology of the In(OH) 3 nanocubes. The size of In(OH) 3 nanocubes is effected by pH value of solution.

Structural and photoluminescence of Mn-doped ZnO single-crystalline nanorods grown via solvothermal method

Mn-doped ZnO nanorods (composition: Mn 0.046Zn 0.954O) were grown by a simple solvothermal technique. The morphological, structural and optical properties of the as-prepared nanorods were investigated by means of transmission electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction, and photoluminescence. The results showed that the sample had rod-like morphology and that the preferential growth direction was along the c-axis. The doping of Mn 2+ ions has significant influences on the optical properties of ZnO nanorods. Low-temperature photoluminescence spectra of Mn-doped ZnO nanorods exhibit a strong near band-edge emission at 370.8 nm and a weak deep-level emission around 525 nm, indicating the concentrations of the defects responsible for deep-level emissions are reduced on doping. The dynamic process of the UV emission for Mn-doped ZnO nanorods was discussed.

Morphological evolution of Nb2O5 in a solvothermal reaction: From Nb2O5 grains to Nb2O5 nanorods and hexagonal Nb2O5 nanoplatelets

Novel Nb2O5 nanorods and polygonal Nb2O5 platelets were generated by a simple solvothermal technique. The geometry evolution of the resultant Nb2O5 from amorphous nanoparticles to crystallized particles, from polygonal platelets to well-elongated nanorods was been studied in detail. The processing parameters, including the reaction temperature, reaction time, concentration of the precursors, and pH value of the solution, which affect the shape and size of the nanorods, were investigated. The Nb2O5 nanorods with different aspect ratios were examined by XRD, SEM and TEM. The experimental results show that Nb2O5 nanorod is the orthorhombic structure and well-crystallized. The growth of the nanorods follows their [001] direction. The successful generation of high quality Nb2O5 nanorods is not only important for transition metal oxide research, but also potentially important for further formation of new Nb-based 1-D nanostructures, such as NbS2 and NbN.

Thermal Expansion Behaviors of Bismuth Nanowires

The linear and volumetric thermal expansion coefficients of bismuth nanowire and nanoflower have been measured from 298 to 478 K by high-temperature X-ray diffraction methods. The bismuth nanowire and nanoflower were prepared by a simple solvothermal technique. It was found that the linear and volumetric thermal expansion coefficient of the nanowire decreases initially, then increases, and decreases finally with increasing temperature. The nanowire and nanoflower possess smaller linear thermal expansion coefficient in the a-axis direction in the whole measured temperature range and in the c-axis direction at high temperature as compared to the conventional bulk bismuth. The volumetric expansion coefficients of the nanowire and nanoflower are always smaller than those of the corresponding bulk materials. The results were discussed on the basis of the contributions from point defects, stress, and valence electrons. Our results demonstrated that the anisotropic thermal expansion behavior of bismuth nanowires is an intrinsic property.

Synthesis of Nb 3.49N 4.56O 0.44 nanoplatelets and NbS 2–Nb 2O 5 nanoflakes

Novel polygonal Nb 2O 5 platelets have been generated by a simple solvothermal technique. Then, the polygonal Nb 2O 5 nanoflakes as a template react chemically with NH 3 and H 2S to generate polygonal Nb 3.49N 4.56O 0.44 nanoflakes and the polygonal NbS 2–Nb 2O 5 nanoflakes. Under optimal conversion conditions, the final geometry features of polygonal Nb 3.49N 4.56O 0.44 nanoflakes and the polygonal NbS 2–Nb 2O 5 nanoflakes are predetermined by the size and morphology of the Nb 2O 5 platelets. TEM observation has showed that the Nb 2O 5 nanoplatelets and Nb 3.49N 4.56O 0.44 nanoflakes consist of well-crystallized single crystals, the polygonal NbS 2–Nb 2O 5 nanoflakes are composed of phases of mixed oxide and sulphide. These new polygonal plate-like nanostructures are important for understanding nanostructure processing.

Self-assembled one-dimensional carbon nitride architectures

Three kinds of assembled one-dimensional carbon nitride architectures were realized in large scale by a simple solvothermal technique. Carbon nitride nanotube bundles were formed involving the reaction of cyanuric chloride (C 3N 3Cl 3) with sodium at 230 °C and 1.8 MPa in a stainless steel autoclave using NiCl 2 as a catalyst precursor. Without any catalyst, aligned nanoribbons were formed at 290 °C and 3 MPa, and microspheres consisting of hundreds of nanoribbons were formed at 260 °C and 3.5–4.5 MPa. The electron energy-loss spectroscopy (EELS) proved all these 1-D carbon nitride nanostructures are consistent with the stoichiometry of CN. The similarity and difference of their microstructures and optical properties were researched by FTIR, Raman, PL measurements and UV–vis absorption spectra. These assembled CN architectures with well-controlled dimensionality and luminescent property may have potential uses as component of optical nanoscale devices. Their formation mechanisms were briefly discussed.