Wulin Song

SYNTHESIS AND GAS SENSITIVITY OF IN-DOPED ZNO NANOPARTICLES

Undoped and In-doped ZnO nanoparticles were produced by renovated hybrid induction and laser heating (HILH) in this study from Zn–In alloy, with different mole ratios, as the raw material in a flowing mixed gas atmosphere of Ar+O2. The morphological characteristics, phase microstructure, and chemical state of In-doped ZnO nanoparticles were investigated by transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The change in electrical resistance of thick film based on the In-doped ZnO nanoparticles and their gas sensitivities to volatile organic compounds (VOCs), benzene, acetone, ethyl alcohol, toluene, and xylene, as a function of temperature were measured in the temperature range of 200–500 °C, and compared with the undoped thick film. The results showed that the In-doped ZnO has lower resistance and higher sensitivity than that of the undoped ZnO. This was probably due to the fact that the In3+ ions, replacing the Zn2+ ions in the ZnO lattice, resulted in an increase of the concentration of free electrons followed by an increase of the adsorbed oxygen. Among the types of In-doped ZnO, 4.58 at % In-doped ZnO had the lowest resistance, and had the highest sensitivity. On increasing the concentration of In into ZnO, its resistance increased, while the sensitivity decreased. The sensitivity of the 4.58 at % In-doped ZnO to VOCs was in the order of acetone>alcohol>xylene>toluene> benzene at an operating temperature of 420 °C.

Characteristics of Sb2O3 nanoparticles synthesized from antimony by vapor condensation method

Abstract Sb 2 O 3 nanoparticles with an average size of approximately 80 nm were synthesized by vapor condensation method. The characteristics were investigated by means of TEM, XRD, differential thermal analysis (DTA), X-ray photoelectron spectrometer (XPS) and Raman spectroscopy. The exothermic peak temperature for the nanopowder is lower than that of the micropowder, its reactive temperature span is narrower and oxidizing exothermic heat is larger due to the nano-sized effect. XPS analysis shows that a few amount of antimonies are still in metallic states as the interstitial antinomy atoms in the nanoparticles. The interstitial atoms may be mainly responsible for the red shifts (3–6.4 cm −1 ) of the characteristic peaks in the Raman spectrum.

Thermal property and microstructure of Al nanopowders produced by two evaporation routes

Abstract Al nanopowders with diameters ranging from 20 to 50 nm passivated by Al2O3 coatings were produced by two different evaporation routes: induction heating evaporation (IHE) and laser-induction complex heating evaporation (LCHE). Thermal property of the nanopowders was investigated by differential thermal analysis (DTA) in dry oxygen environment. The results show that Al nanopowders produced by LCHE have the oxidation enthalpy change (ΔH) of 3.54 kJ/g, while the ΔH of Al produced by IHE is 1.18 kJ/g. The phase constitution and microstructures of these nanopowders were revealed using X-ray diffraction (XRD) analysis, transmission electronic microscopy (TEM) and high-resolution transmission electronic microscopy (HRTEM). The results show that the two powders have the same composition and mean particle size, as well as the thickness of Al2O3 coatings (3–5 nm). Defects were observed on the surfaces of the particles by LCHE. However, the defects were not detected by HRTEM on the surfaces of the particles by IHE. The results prove that there exists excessive stored energy in Al nanopowders by LCHE because of the nonequilibrium condition brought by laser and the defects are the storage area of the excessive stored energy. Propellants composed of Al nanopowders by LCHE show higher energy level and specific impulse.

Oxidation reaction during laser cladding of SAE1045 carbon steel with SiC/Cu alloy powder

Laser cladding of SAE1045 carbon steel with SiC/Cu alloy powder was performed in air. The microstructures of the cross-section of the clad layer obtained were obviously divided into three laminae. Analysis results using X-ray diffraction, scanning electron microscope (SEM) and electron probe microanalysis (EPMP) indicate that there exist α-Cu, SiO2 and Cu5Si in the top layer. However, SiC particles (SiCp) originally added almost disappeared during laser cladding. To simulate the reaction taken place in the laser pool, differential thermal analysis was carried out by using a Perkin-Elmer DSC 7 in an atmosphere of Ar and O2. This revealed that the SiCp is stable during heating in the atmosphere of Ar. However, intensive oxidation and decomposition of the SiCp were found when heating was undertaken in an O2 atmosphere, which reasonably explains the formation of SiO2 and Cu5Si in the top layer.

Enhanced visible-light photocatalytic performance of highly-dispersed Pt/g-C3N4 nanocomposites by one-step solvothermal treatment

A highly dispersed Pt/g-C3N4 nanocomposite photocatalyst was successfully prepared by depositing platinum nanoparticles (NPs) onto the surface of g-C3N4 with uniform size. The nanocomposites were applied as an efficient visible-light-driven photocatalyst for the degradation of methyl orange (MO) and tetracycline hydrochloride (TC). The sample with a Pt loading amount of 2% exhibited the highest photocatalytic performance, about 7.82 (MO) and 4.30 (TC) times higher than that of the pure g-C3N4. The enhancement of the photocatalytic performance was attributed to the rapid separation of generated electron hole pairs resulting from the hybrid effect, which was confirmed by XPS spectra, photocurrent response experiment, electrochemical impedance spectroscopy measurements and photoluminescence spectra. As confirmed by X-ray photoelectron spectroscopy, there is a strong interaction between Pt NPs and g-C3N4; the delocalized pi bond in g-C3N4 with a high local electron density donates lone pair electrons to the empty d orbitals of Pt atoms. The combination between g-C3N4 and Pt promotes the separation of electron–hole pairs.