Ji Wu

Benzene-thermal route to carbon nanotubes at a moderate temperature

Carbon nanotubes are novel nanoscale materials that carbon nanotubes with an inner diameter of 5–15 nm and many researchers have been interested in since the first outer diameter of 10–35 nm, respectively. The average report of their discovery [1]. They have various potential tube length is up to 1.5 mm. The carbon nanotubes applications, such as electronics, composite fabrication and synthesized in this work have open ends and slightly gas storage [2–5]. thicker walls. The SAED pattern from the nanotube Among the different preparation methods for carbon bundles (inset in Fig. 1a) shows two rings which correnanotubes, such as catalytic pyrolysis [6–8], electric arc spond to (002) and (101) graphite planes according to the discharge [9,10], laser ablation [11,12], chemical vapor JCPDS-41-1487. deposition [13,14] and hydrothermal [15–18] methods, the A typical HRTEM image of the nanotube (inset in Fig. catalytic routes seem to be the most promising for large 1b) reveals the tube walls are made of about 40 graphite scale production. The solvothermal method [19,20] is also layers. The interlayer spacing in the MWNT wall is about a catalytic route with a moderate temperature, which often 0.337 nm, which is a little less than the typical (002) needs strong reductants such as Na or K and expensive lattice distance in hexagonal graphite. carbon sources such as C Cl or C Cl . There are catalyst particles encapsulated at the tips of 6 6 2 4 In this study, we used commercial benzene as carbon the tubes, as shown in Fig. 1a. The higher magnification source and Ni–Fe alloy as catalyst to synthesize carbon (Fig. 1c) shows a representative tube with a catalyst nanotubes. This process was carried out under benzeneparticle at its root end. It is reasonable to think that thermal conditions without the use of reductant. The nanotubes grew from the catalyst particles. The SAED products were characterized by XRD, TEM, HRTEM and pattern of the same area (inset in Fig. 1c) is a mixture of Raman spectrum. graphite and Ni–Fe alloy patterns. There exist two rings Micro-size nickel–iron alloy (0.5 g; 46%wt Ni) powder which correspond to (002) and (101) planes of carbon and 12 ml C H were placed in a stainless steel autoclave nanotubes. The diffraction spots can be indexed as (111) 6 6 with a capacity of 20 ml. The autoclave was kept at 480 8C and (220) reflections of the Ni–Fe alloy according to for 12 h under a reaction pressure of about 15 MPa, and JCPDS 23-297. then cooled to room temperature naturally. The resultant EDX analysis (Fig. 1d) of the catalyst indicated that was collected from the autoclave, and then the Ni–Fe alloy they were made up of Fe and Ni and the average atomic powders were removed according to the difference of ratio of Fe:Ni was about 61:39 (the instrumental error is densities resulting in about 2.1 g of carbonous products. about 65%). The carbon in the EDX spectrum was from HRTEM images, SAED patterns and EDX spectra were the nanotubes, while Cu was from the copper grid, and O obtained using a transmission electron microscope. The from the surface adsorption of carbon nanotubes and TEM images (Fig. 1a, b) show that reaction products are catalyst. The carbonous products were used directly to record the Raman spectrum (Fig. 2) at room temperature using a *Corresponding author. Tel.: 186-551-360-1589; fax: 186confocal laser Raman microspectrometer with an argon-ion 551-360-7402. E-mail address: smw@mail.ustc.edu.cn (Y. Qian). laser at an excitation wavelength of 514.5 nm. There exist

Sonochemical synthesis of nanocrystalline lead chalcogenides: PbE (E = S, Se, Te)

Abstract Nanocrystalline lead chalcogenides PbE (E=S, Se, Te) were synthesized conveniently by the reaction of Pb(CH3COO)2·3H2O and elemental chalcogens in ethylenediamine (en) under ultrasonic irradiation. XRD and TEM techniques were employed to characterize the products. The solubility of chalcogen in en was found to be the key factor of the reaction. A three-step mechanism was proposed to account for the formation of the products.

Shape-controlled synthesis of BaWO4 crystals under different surfactants

BaWO4 crystals with different morphology, such as olive-like, flake-like, and whisker-like structure have been successfully prepared through a hydrothermal process in the presence of different surfactants—C17H33COOK, C19H39COOK, and C25H51COOK, respectively. X-ray powder diffraction (XRD) shows that the crystals have been well crystallized. The observation results of scanning electron microscopy (SEM) on the obtained samples have revealed that the selection of surfactants and the concentration of the starting materials can highly affect the morphology and size of BaWO4 crystals.

The synthesis of CdS/ZnO and CdS/Pb3O4 composite materials via microwave irradiation

Abstract CdS/ZnO, CdS/Pb 3 O 4 composite materials via microwave irradiation were fabricated. The main process was that CdS nanoparticles connected with each other via van der Waals’ action under the induction of microwave irradiation to form CdS cages. CdS cages adsorbed nitrate solutions, which transformed to oxides by calcination and formed CdS/ZnO and CdS/Pb 3 O 4 composite materials. Both CdS and ZnO photoluminescence emissions were observed simultaneously.

Microwave-templated synthesis of CdS nanotubes in aqueous solution at room temperature

CdS nanotubes were synthesized via a new method, which employed TM01-type microwave irradiation as a template. The reactions were completed in aqueous solution at room temperature. The products were investigated with X-ray diffraction, transmission electron microscopy and high-resolution transmission electron microscopy. The formation mechanism of CdS nanotubes with a face centered cubic structure is proposed.

Synthesis of nano-fibrillar bismuth sulfide by a surfactant-assisted approach

Bi2S3 nanofibers with a diameter less than 10 nm and lengths ranging from 400 to 1000 nm were successfully prepared by a convenient solution route at 90 °C by using BiCl3 and thiourea as the starting materials. The product was characterized by XRD, XPS, and TEM techniques. It was found that anionic surfactant C17H33COOK played an important role in controlling the morphology of the product. The formation of the nanofibers could be well explained by the accordion-like folding mechanism.

A solvent-reduction approach to tetrapod-like copper(I) chloride crystallites

Tetrapod-like CuCl crystallites with uniform sizes were generated conveniently in a mixed solution of acetylacetone and ethylene glycol at 120 °C under solvothermal conditions. The products were characterized by XRD, XPS, SEM, UV–Vis and PL techniques. The average length of the legs of T-CuCl is 30 µm. The morphologies of the products were related to the reaction temperature, time and the volume ratio of the solvents. A solvent-mediated morphological transformation mechanism was proposed and it was in good agreement with the observations made with scanning electron microscopy. The role of the two solvents was also explored.

Heat switch effect in an antiferromagnetic insulator Co3V2O8

We report a heat switch effect in single crystals of an antiferromagnet Co3V2O8, that is, the thermal conductivity (κ) can be changed with magnetic field in an extremely large scale. Due to successive magnetic phase transitions at 12–6 K, the zero-field κ(T) displays a deep minimum at 6.7 K and rather small magnitude at low temperatures. Both the temperature and field dependencies of κ demonstrate that the phonons are strongly scattered at the regime of magnetic phase transitions. Magnetic field can suppress magnetic scattering effect and significantly recover the phonon thermal conductivity. In particular, a 14 T field along the a axis increases the κ at 7.5 K up to 100 times. For H∥c, the magnitude of κ can be suppressed down to ∼8% at some field-induced transition and can be enhanced up to 20 times at 14 T. The present results demonstrate that it is possible to design a kind of heat switch in the family of magnetic materials.

Thermal conductivity of the diamond-chain compound Cu3(CO3)2(OH)2

Thermal conductivity (κ) of a distorted spin diamond-chain system, Cu3(CO3)2(OH)2, is studied at low temperatures down to 0.3 K and in magnetic fields up to 14 T. In zero field, the κ(T) curve with heat current along the chain direction has very small magnitudes and shows a pronounced three-peak structure. The magnetic fields along and perpendicular to the chains change the κ strongly in a way having good correspondence to the changes of magnetic specific heat in fields. The data analysis based on the Debye model for phononic thermal conductivity indicates that the heat transport is due to phonons and the three-peak structure is caused by two resonant scattering processes by the magnetic excitations. In particular, the spin excitations of the chain subsystem are strongly scattering phonons rather than transporting heat.

A comparative study of ultra-low-temperature thermal conductivity of multiferroic orthoferrites RFeO3 (R = Gd and Dy)

Ultra-low-temperature thermal conductivity (κ) of GdFeO3 and DyFeO3 single crystals is studied down to several tens of milli-Kelvin. It is found that the κ is purely phononic and has strong magnetic-field dependence, indicating a strong spin-phonon coupling. Moreover, the low-T κ(H) with H∥c show rather different behaviors in these two materials. In particular, the κ of GdFeO3 can be strongly enhanced in several tesla field and becomes weakly field dependent in higher fields up to 14 T; whereas, the κ of DyFeO3 is continuously suppressed with increasing field and does not show any signature of recovery at 14 T. The results can be well understood by the difference in the spin anisotropy of Gd3+ and Dy3+ ions.