4 research outputs found
Diffusion doping of cobalt in rod-shape anatase TiO\u3csub\u3e2\u3c/sub\u3e nanocrystals leads to antiferromagnetismâ€
Cobalt(II) ions were adsorbed to the surface of rod-shape anatase TiO2 nanocrystals and subsequently heated to promote ion diffusion into the nanocrystal. After removal of any remaining surface bound cobalt, a sample consisting of strictly cobalt-doped TiO2 was obtained and characterized with powder Xray diffraction, transmission electron microscopy, UV-visible spectroscopy, fluorescence spectroscopy, X-ray photoelectron spectroscopy, SQUID magnetometry, and inductively-coupled plasma atomic emission spectroscopy. The nanocrystal morphology was unchanged in the process and no new crystal phases were detected. The concentration of cobalt in the doped samples linearly correlates with the initial loading of cobalt(II) ions on the nanocrystal surface. Thin films of the cobalt doped TiO2 nanocrystals were prepared on indium-tin oxide coated glass substrate, and the electrical conductivity increased with the concentration of doped cobalt. Magnetic measurements of the cobalt-doped TiO2 nanocrystals reveal paramagnetic behavior at room temperature, and antiferromagnetic interactions between Co ions at low temperatures. Antiferromagnetism is atypical for cobalt-doped TiO2 nanocrystals, and is proposed to arise from interstitial doping that may be favored by the diffusional doping mechanism
Kirkendall Growth of Hollow Mn<sub>3</sub>O<sub>4</sub> Nanoparticles upon Galvanic Reaction of MnO with Cu<sup>2+</sup> and Evaluation as Anode for Lithium-Ion Batteries
We
report the formation of high surface area hollow Mn<sub>3</sub>O<sub>4</sub> nanoparticles that form as a result of the galvanic
reaction of Cu<sup>2+</sup> with MnO nanocrystals concomitant with
a nanoscale Kirkendall effect. The MnO nanocrystals were prepared
according to the ultralarge scale synthesis reported by Hyeon, which
allowed the preparation of hollow Mn<sub>3</sub>O<sub>4</sub> in multigram
quantities. Ex-situ analyses with transmission electron microscopy
and powder X-ray diffraction show the morphology and phase stability
of the hollow particles correlate with DSC-TGA data and show collapse
of the hollow particles at temperatures greater than 200 °C.
Electrodes fabricated from hollow Mn<sub>3</sub>O<sub>4</sub> exhibited
excellent initial Li ion storage capability (initial discharge capacity
= 1324 mAh/g) but poor cycling performance (97% loss of discharge
capacity after 10th cycle), whereas Mn<sub>3</sub>O<sub>4</sub>-MWCNT
electrodes exhibited good reversibility and discharge capacity of
760 mAh/g after 100 cycles
Quantitative Attachment of Bimetal Combinations of Transition-Metal Ions to the Surface of TiO<sub>2</sub> Nanorods
We
report the sequential, quantitative loading of transition-metal
ions (Cr<sup>3+</sup>, Mn<sup>2+</sup>, Fe<sup>2+</sup>, Co<sup>2+</sup>, Ni<sup>2+</sup>, and Cu<sup>2+</sup>) onto the surface of rod-shaped
anatase TiO<sub>2</sub> nanocrystals in bimetallic combinations (<sub>6</sub><i>C</i><sub>2</sub> = 15) to form M,M′-TiO<sub>2</sub> nanocrystals. The materials were characterized with transmission
electron microscopy (TEM), powder X-ray diffraction (XRD), elemental
analysis, X-ray photoelectron spectroscopy (XPS), and UV–visible
spectroscopy. TEM and XRD data indicate that the sequential adsorption
of metal ions occurs with the retention of the phase and morphology
of the nanocrystal. Atomistic models of the M,M′-TiO<sub>2</sub> nanocrystals were optimized with density functional theory calculations.
Calculated UV–visible absorption spectra and partial charge
density maps of the donor and acceptor states for the electronic transitions
indicate the importance of metal-to-metal charge transfer (MMCT) processes