Hougang Fan

A novel approach to the synthesis of CoPt magnetic nanoparticles

L10 CoPt nanoparticles with face-centred tetragonal (FCT) structure are synthesized by the sol–gel method. Differential thermal analyses show the dehydration of various water molecules and decomposition/combustion of organic groups at a temperature below 600 °C and melting of Co and Pt at 700 °C. X-ray diffraction results show a transition from face-centred cubic to the FCT phase and an increase in particle size with increasing temperature. Transmission electron microscope (TEM) images show that highly monodisperse particles are obtained. High-resolution TEM (HRTEM) images reveal the appearance of L10 ordered phase at temperatures above 600 °C. The survey scans of x-ray photoelectron spectroscopy show that no magnetic impurity is detected within the detection limit. The maximum coercivity (353 344 A m−1) is obtained for the samples heated at 800 °C. The relationship between the temperature and the structure is discussed and the possible growth mechanism is given in terms of atomic diffusion.

Synthesis and optical properties of Ce-doped ZnO

ZnO nanorods were synthesized using the sol-gel method, and the effects of annealing temperature and Ce doping on the morphologies and optical properties of ZnO nanostructures were investigated in detail. The XRD measurements showed that the as-synthesized ZnO nanostructures had a hexagonal wurtzite structure. SEM images showed that uniform nanorods formed at 900 °C. Photoluminescence measurements showed an ultraviolet emission peak and a relatively broad visible light emission peak for the samples sintered at different temperatures. The UV emission peak bathochromically shifted when the annealing temperature rose from 850 to 1000 °C. Ce doping decreased the synthesized temperature of the ZnO nanorods to 500 °C, and the UV peaks hypsochromically shifted.

Preparation and Luminescence Behavior of CaSiO3:Eu3+ (Bi3+)

CaSiO3: Eu3+0.002 with a monoclinic perovskite structure was synthesized by using sol-gel method, and its luminescence characteristics were investigated. From the excitation spectrum, it can be seen that the main peaks located at 238, 396, 415, 437 and 359 nm correspond to the charge-transfer band of Eu3+—O2-, the absorption transitions of 7F0,1→5L6, 7F0→5D3, 7F1→5D3 of Eu3+ ions, and cP1→aS0 of Bi3+ ions, respectively. When the samples were excited with a light of wavelength 359 or 395 nm, it can be seen from the emission spectrum that the electronic dipole transition located at 609 nm corresponding to 5D0→7F2 of Eu3+ ions was stronger than the magnetic dipole transition located at 587 nm corresponding to 5D0→7F1 of Eu3+ ions, which shows that more Eu3+ ions were located in nonreversion center lattices. The energy transfer from Bi3+ ions to Eu3+ ions in the phosphor was also discussed. The results show that Eu3+ ions could be well sensitized by Bi3+ ions, and the energy-transfer pattern between Bi3+ ions and Eu3+ ions was resonance energy transfer.

Mesoporous TiO2 coated ZnFe2O4 nanocomposite loading on activated fly ash cenosphere for visible light photocatalysis

Several activated fly ash cenosphere (AFAC) supporting TiO2 coated ZnFe2O4 (TiO2/ZnFe2O4/AFAC) photocatalysts were prepared by sol–gel and hydrothermal methods. These photocatalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), UV-vis diffuse reflectance spectroscopy (UV-DRS) and nitrogen adsorption analyses for Brunauer–Emmett–Teller (BET) specific surface area measurements. We found that the main components of spherical AFAC were mullite (Al6Si2O13) and SiO2; the crystallite size of the TiO2/ZnFe2O4 nanocomposite was less than 10 nm and its specific surface area was 162.18 m2 g−1. The TiO2/ZnFe2O4 nanocomposite had a band-gap of 2.56 eV, which would photodegrade 95% of rhodamine B (RhB) under visible light within 75 min. When hybridized with 0.02 g AFAC, the TiO2/ZnFe2O4/0.02 g AFAC photocatalyst with a band-gap of 2.50 eV could remove 97.1% of RhB and be reused three consecutive times with minor decrease in photocatalytic performance. However, the photocatalytic performance decreased to 91.0% on increasing the dosage of AFAC to 0.30 g. The mesoporous structure of all the photocatalysts and the strong adsorption ability of AFAC accounted for the notable performance.

Low-temperature growth and optical properties of Ce-doped ZnO nanorods

Ce-doped ZnO nanorod arrays were grown on zinc foils by a hydrothermal method at 180°C. The effects of Ce-doping on the structure and optical properties of ZnO nanorods were investigated in detail. The characterisation of the rod array with X-ray diffraction and X-ray photoelectron spectroscopy indicated that Ce3+ ions were incorporated into the ZnO lattices. There were no diffraction peaks of Ce or cerium oxide in the pattern. From UV-Vis spectra, we observed a red shift in the wavelength of absorption and decreased band gap due to the Ce ion incorporation in ZnO. The photoluminescence integrated intensity ratio of the UV emission to the deep-level green emission (I UV/I DLE) was 1.25 and 2.87, for ZnO and Ce-doped ZnO nanorods, respectively, which shows a great promise for the Ce-doped ZnO nanorods with applications in optoelectronic devices.Ce-doped ZnO nanorod arrays were grown on zinc foils by a hydrothermal method at 180°C. The effects of Ce-doping on the structure and optical properties of ZnO nanorods were investigated in detail. The characterisation of the rod array with X-ray diffraction and X-ray photoelectron spectroscopy indicated that Ce3+ ions were incorporated into the ZnO lattices. There were no diffraction peaks of Ce or cerium oxide in the pattern. From UV-Vis spectra, we observed a red shift in the wavelength of absorption and decreased band gap due to the Ce ion incorporation in ZnO. The photoluminescence integrated intensity ratio of the UV emission to the deep-level green emission (I UV/I DLE) was 1.25 and 2.87, for ZnO and Ce-doped ZnO nanorods, respectively, which shows a great promise for the Ce-doped ZnO nanorods with applications in optoelectronic devices.

XPS and Raman study of the active-sites on molybdenum disulfide nanopetals for photocatalytic removal of rhodamine B and doxycycline hydrochlride

Molybdenum disulfide (MoS2) nanopetals were successfully synthesized by hydrothermal method (sample without sintering) and then sintered at different temperature (sintered samples). The products were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen (N2) adsorption analyses for Brunauer–Emmett–Teller (BET) specific surface area measurements, X-ray photoelectron spectrum (XPS) and Raman spectrum. XRD pattern indicated that the samples can be indexed to hexagonal phase 2H-MoS2. SEM and TEM images showed that the sintered MoS2 nanopetals had sizes ranging from 150 to 300 nm with almost the same morphology. The pore structure and surface area were nearly the same for the three sintered MoS2 nanopetals. Interestingly, XPS and Raman spectra implied that there was a few 1T-phase in the MoS2 nanopetals which enhanced the photocatalytic performance greatly when sintered at low temperature.