Showing papers by "Xianting Zeng published in 2007"

Surface modifications of ZnO quantum dots for bio-imaging

Abstract: The wide bandgap and large exciton binding energy of ZnO may generate new applications in bio-imaging after careful surface modifications. Formation of chemically pure ZnO colloidal nanocrystals with controlled size without unwanted by-products or agglomeration has been the major challenge to fully utilize ZnO's unique properties. In this research, colloidal ZnO nanocrystals were synthesized by a soft chemical method. Particle size and colloidal stability were controlled by capping agents. Influences of the surface modifications on particle size, size distribution and photoluminescence properties were investigated. Pure ZnO showed high intensity UV emission and very low intensity in the visible range, indicating good surface morphology of the ZnO nanoparticles with little surface defects. Transmission electron microscopy (TEM) analysis revealed that the capped crystals were close to spherical shape with single-crystal size about 6 nm. X-ray diffraction (XRD) analyses revealed single-phase ZnO nanoparticles. For bio-imaging, emission in visible wavelength range is preferred. Both TiO2 and SiO2 were effective in shifting the emission peak to the visible range with high intensity. Optimum capping thickness is 0.5 nm. ZnO–TiO2 quantum dots (QDs) showed good bio-imaging capability on plant cells. Quantum yields of the pure ZnO and TiO2 capped ZnO were measured and compared to commercial fluorescence materials.

Steam-Assisted Solid Wet-Gel Synthesis of High-Quality Nanorods of Boehmite and Alumina

Abstract: A simple solid-phase method was developed for synthesis of high-quality boehmite nanorods by steam-assisted wet-gel conversion process γ-Al2O3 nanorods with clear-cut edge have been successfully obtained by thermal treatment of boehmite nanorods at 600 °C for 5 h The nanorods of boehmite and γ-Al2O3 were characterized by X-ray diffraction (XRD), Raman spectroscopy, and field emission scanning electron microscope (FESEM) with energy-dispersive spectroscopy (EDS), transmission electron microscopy (TEM), and high-resolution tranmission electron microscopy (HRTEM) with selected area electron diffraction (SAED) spectroscopy, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR), magic-angle spinning (MAS) 27Al nuclear magnetic resonance (NMR), and thermogravimetric and differential thermal analysis (TGA-DTA) The growth of boehmite was found to be greatly affected by the conditions used for precipitation of Al(NO3)3 with NH4OH aqueous solution When precipitation was conducted under pH 5

Solid-phase low temperature steam-assisted synthesis of thermal stable alumina nanowires.

Abstract: A simple steam-assisted solid phase synthesis method was developed for synthesis of boehmite nanowires in the presence of TEAOH surfactant The boehmite nanowires had uniform diameters (12-16 nm) and length up to 1-2 microm The morphology of the nanostructured wires was well preserved after being converted to pure gamma-Al2O3 by thermal treatment at 600 degrees C for 5 h The nanowires of Al2O3 exhibited excellent thermal stability by retarding the phase transformation and maintaining the wires-like nanostructure after being aged up to 1300 degrees C by preventing sintering between particles at high temperatures The surface areas of Al2O3 nanowires could be maintained as high as 68 m2/g at 1300 degrees C while the surface areas of Al2O3 micropowder shrank to 089 m2/g after same thermal treatment Both in-situ XRD and 27Al NMR results indicated that the crystal structure of gamma-Al2O3 nanowires was not transformed to alpha-Al2O3 at 1300 degrees C whereas micropowder Al2O3 was fully converted to alpha-Al2O3 at 1100 degrees C