Shuangping Yi

Hydrogen storage for carbon nanotubes synthesized by the pyrolysis method using lanthanum nickel alloy as catalyst

We have investigated the adsorption of hydrogen of multiwall carbon nanotubes synthesized by the pyrolysis method using a lanthanum nickel hydrogen storage alloy as a catalyst. The mechanism of carbon nanotubes synthesized using a La–Ni alloy catalyst is discussed. In the hydrogen atmosphere and high-temperature process of carbon nanotube preparation, the LaNi5 alloy particle may be changed into an intermetallic compound of Ni and La by the analysis of the x-ray diffraction patterns and energy-dispersive x-ray spectroscopy of the nanotubes samples using a La–Ni alloy as a catalyst. The H2 uptake capacity of the carbon nanotubes using a La–Ni alloy catalyst is about 5 wt % through to the pressure of 10 MPa. Using a La–Ni alloy as a catalyst increases the effect of chemistry adsorption in the H2 adsorption of the La–Ni alloy catalyzed carbon nanotubes. The P–C–T curve has an approximate plateau. The La–Ni alloy catalyzed carbon nanotubes have better activation for H2 uptake and larger hydrogen uptake in com...

Effect of Annealing on the Discharging Performance of Carbon Nanotubes for Nickel Hydrogen Secondary Battery Negative Material

The effect of annealing temperature for carbon nanotubes (CNTs) in vacuum on its performance as a nickel hydrogen battery negative material is investigated by high resolution transmission electron microscopy (HRTEM), Raman, and discharge capacity. The electrochemical discharge performance of CNTs can be improved by annealing treatment because of few amorphous carbon impurities and defects in annealed CNTs by observations of HRTEM and Raman spectra. With the increase in annealing temperature, the discharge capacity increases initially and then decreases. The optimum annealing temperature is around 750°C. Among investigated CNTs with different diameters, the effect of annealing on the discharge performance for CNTs with a diameter of 40-60 nm is most significant. It has the best discharging capacity of 585 mAh/g with annealing at 750°C, which is 1.4 times compared to CNTs without annealing. The discharging performance of annealed CNTs under different discharging currents is also investigated. The annealed CNT electrodes at 750°C still have 300 mAh/g discharging capacity in a discharging current of 2000 mA/g, showing that annealed CNTs have good discharging performance under great current discharging.

Enhancing persistent luminescence and photocatalytic properties in Ti as a trap center in ZnGa2O4

ZnGa2O4 and ZnGa2O4:Ti phosphors were synthesized by the solid state method, and their persistent luminescence and photocatalytic properties were investigated in detail. The results of this study showed that Ti4+ doping improved the persistent luminescence properties. Thermoluminescence measurements demonstrated that the trap concentration considerably increased upon incorporation of Ti4+ ions into the ZnGa2O4 lattice. The traps generated by Ti doping were responsible for improvement in persistent luminescence. Furthermore, photocatalytic activity tests showed that the Ti-doped ZnGa2O4 phosphor exhibited much higher photocatalytic activity than the ZnGa2O4 host. UV–Vis diffuse reflectance spectra demonstrated that Ti-doped ZnGa2O4 shown a higher UV absorption efficiency. A comparison between the density of states of ZnGa2O4:Ti and ZnGa2O4 revealed that the bottom of the conduction band was modified by Ti doping. Hence, it could be concluded that Ti doping enhanced light harvest capability to generate more electron–hole pairs, and acted as a trap center by decreasing the recombination of photogenerated electrons and holes, resulting in the enhancement of both persistent luminescence and photocatalytic activity.

Synthesis and photoluminescence properties of multicolor tunable GdNbO4: Tb3+, Eu3+ phosphors based on energy transfer

A color-tunable phosphor based on Tb3+/Eu3+ co-doped GdNbO4 were synthesized by a traditional solid-state reaction method. X-ray powder diffraction (XRD), diffuse reflectance spectra, photoluminescence spectra and decay curves were utilized to characterize the as-prepared phosphors. XRD result indicated that various concentrations Tb3+/Eu3+ single-doped and co-doped phosphors were well indexed to the pure GdNbO4 phase. The GdNbO4 host was proved to be a self-activated phosphor with broad absorption range from 200 nm to 325 nm. When Tb3+ ions were added into the host lattice, the energy transferring from host to Tb3+ was identified. And the broad absorption in the UV region was changed and enhanced. Therefore, we selected Tb3+ as the sensitizer ion, and adjusted red component from Eu3+ to control the emission color. The energy transfer from Tb3+ to Eu3+ was confirmed based on the luminescence spectra and decay curves. Furthermore, the energy transmission mechanism was deduced to be the dipole–quadrupole interaction. On the whole, the obtained GdNbO4, GdNbO4:Tb3+, and GdNbO4:Tb3+, Eu3+ phosphors may have potential application in the UV white-light-emitting diodes (w-LEDs) and display devices.