Jimin Du

Fabrication and characterization of magnetic carbon nanotube composites

Magnetic carbon nanotube (CNT) composites have been successfully fabricated by employing a one-step approach, in which ferrocene decomposed at high temperatures of 350 °C, 425 °C, 500 °C, and transformed into iron oxides to deposit on CNTs. The resulting products were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, scanning electron microscopy and transmission electron microscopy (TEM). It was found that CNT–maghemite composites sheathed with amorphous carbon-based material were achieved at 500 °C. TEM observation indicated that the produced maghemite particles not only decorated the external walls of CNTs but also were encapsulated within CNTs. The magnetic phase, size and amount of magnetic nanoparticles deposited on the CNTs could be controlled by varying the processing temperature. Magnetic measurements demonstrated that the composites prepared at 500 °C were ferromagnetic, while the composites obtained at 350 °C and 425 °C became superparamagnetic and showed no remanence or coercivity.

Synthesis and characterization of TiO2-montmorillonite nanocomposites and their application for removal of methylene blue

TiO2–montmorillonite (MMT) nanocomposites were successfully prepared via impregnating titanium tetrabutyloxide into the interlayers of MMT with the aid of supercritical ethanol, followed by hydrolysis of the precursor in water and calcination at 500 °C. The X-ray diffraction analysis and electron microscopy observation indicated that the layered structure of MMT was destroyed to some extent in the composites. High-resolution transmission electron microscopy observation showed that the TiO2 particles with size of less than 5 nm were loaded in the exfoliated layers of MMT. The UV absorption edge of TiO2–MMT composites showed a blue shift in the range of 325–275 nm, compared to that of TiO2 particles. The efficiency of the TiO2–MMT composites to remove methylene blue from its aqueous solution was investigated under UV irradiation. It was demonstrated that the as-prepared samples exhibited high efficiency to remove methylene blue due to the adsorptive capacity of MMT and the catalytic degradation ability of TiO2 for methylene blue.

Replication of biological organizations through a supercritical fluid route

A novel and simple method to replicate biological organizations (cotton and pollen grains) with high precision was proposed, in which the precursor dissolved in supercritical CO2 reacted with the surface active groups and adsorbed surface water on biological templates, followed by in situ SCF extraction of the byproducts and unreacted precursor, resulting in inorganic replicas faithfully copying both the macro- and microstructures of the biotemplates.

Structural, magnetic and magnetostrictive properties of Co-doped Tb1-xHoxFe2 (0 ≤ x ≤ 1.0) alloys

Structural, magnetic, and magnetostrictive properties of Tb1-xHox(Fe0.8Co0.2)2 (0 ≤ x ≤ 1.0) alloys have been investigated by means of x-ray diffraction, ac initial susceptibility, an alternating gradient magnetometer and a standard strain gauge technique. A single (Tb,Ho)(Fe,Co)2 Laves phase with a cubic MgCu2-type structure is formed when 0.50 ≤ x ≤ 1.0, while the secondary phase with a PuNi3-type structure occurs at higher Tb content for 0 ≤ x ≤ 0.40. The easy direction of magnetization (EMD) is observed toward 〈111〉 when 0 ≤ x ≤ 0.75, accompanied by a rhombohedral distortion with large spontaneous magnetostriction coefficients λ111. The abnormal λ100 of –550 ppm for x = 0 and as larger than 300 ppm for 0.60 ≤ x ≤ 0.75 were observed, which can be ascribed to the filling of the 3d band due to Co substitution for Fe. The 20 at.% Co substitution for Fe moves the anisotropy compensation point to the Tb-rich side, and increases the Curie temperature TC with about 30 K as compared to the Co-free Tb1-xHoxFe2 ...

Tautomeric equilibrium of ethyl acetoacetate in compressed CO2+ethanol and CO2+methanol mixtures

Tautomerism equilibrium of ethyl acetoacetate (EAA) in compressed CO2 + methanol and CO2 + ethanol mixtures was studied by UV-Vis spectroscopy at 308.15 K and different pressures. The volume expansion coefficient (alpha) of the solvents at different pressures was also determined. The relative permittivity (epsilon) of CO2 + methanol and CO2 + ethanol mixtures at different conditions was calculated using the Kc and Onsager solvent parameter. The equilibrium constant (Kc) of EAA in the binary mixtures increases considerably with increasing pressure or volume expansion coefficient. The relative permittivity or the polarity of the binary mixtures decreases sharply with increasing volume expansion coefficient in the range of 0 < alpha < 1.5. However, as the volume expansion coefficient exceeds 1.5, the relative permittivity decreases slowly. In other words, the dissolution of CO2 in the polar solvents can reduce the polarity of the solvents significantly in the low volume expansion coefficient range, and the polarity of the solution is not sensitive to the volume expansion coefficient as its value is large enough. The difference in polarity of the two solvents reduces with increasing pressure and becomes negligible after volume expansion coefficient exceeds about 2.5.