Search results for "Nanocrystalline material"
showing 6 items of 126 documents
Nanocrystalline ZnCO3—A novel sorbent for low-temperature removal of H2S
2013
Abstract The reactivity of a nanocrystalline ZnCO 3 toward H 2 S (0.2 vol% in N 2 /H 2 mixture) at 140–180 °C was characterized by thermal gravimetric analysis and by breakthrough curves measurements. We have found that under used conditions transformation of ZnCO 3 into ZnS is complete and the rate determining step of the sulfidation is the surface reaction. Such behavior is in strike contrast with that of ZnO whose sulfidation is severely limited by diffusion. The higher reactivity of ZnCO 3 in comparison with ZnO is attributed to the different microstructure of ZnS layer formed in these materials after a partial sulfidation. As in ZnO–ZnS transformation the molar volume increases (from 1…
A study of electron transfer in Ru(dcbpy)2(NCS)2 sensitized nanocrystalline TiO2 and SnO2 films induced by red-wing excitation.
2008
Excited state dynamics and electron transfer from the Ru(dcbpy)2(NCS)2 (RuN3) sensitizer to semiconductor nanoparticles were studied using time-resolved femtosecond absorption spectroscopy. We found that excitation of the red wing of the absorption spectrum of the sensitizer populates the (3)MLCT state directly, both in solution and attached on semiconductor nanoparticle films. Electron injection is slowed down and becomes gradually less efficient as excitation moves towards red from the absorption maximum at 535 nm. At 675 nm the injection is non-exponential and characterized by 5, 30 and 180 ps time constants. The non-exponential electron injection observed is assigned to injection from a…
XAS, XRD, AFM and Raman studies of nickel tungstate electrochromic thin films
2001
Abstract Systematic studies of nanocrystalline nickel tungstate, NiWO 4 , thin films were performed by several experimental techniques such as Ni K- and W L 1,3 -edges X-ray absorption spectroscopy, X-ray diffraction, Raman spectroscopy, atomic force microscopy and cyclic voltammetry measurements. We found that the NiWO 4 thin films exhibit electrochromic properties similar to that of amorphous tungsten trioxide films, but show better structural stability upon multiple colouring/bleaching cycling. It was observed that a nanocrystallinity of the thin films results in strong modifications of the NiO and WO interactions, which affect both local atomic and vibrational structures.
<title>Iridium L<formula><inf><roman>3</roman></inf></formula>-edge and oxygen K-edge x-ray absorption spec…
2003
Structural investigations of the short range order around iridium and oxygen ions in nanocrystalline iridium oxide thin films, prepared by dc magnetron sputtering technique, were performed by x-ray absorption spectroscopy. The Ir L3-edge extended x-ray absorption fine structure and the O K-edge x-ray absorption near edge structure signals were measured at room temperature and analyzed within ab initio multiple-scattering and full-multiple-scattering approaches, respectively. The x-ray absorption spectroscopy results indicate the presence in the films of orderd regions - nanocrystals, having a size of about 10 angstrom and a structure rather close to that in crystalline iridium oxide IrO2. S…
Structural insights into M2O-Al2O3-WO3 (M = Na, K) system by electron diffraction tomography.
2015
TheM2O–Al2O3–WO3(M= alkaline metals) system has attracted the attention of the scientific community because some of its members showed potential applications as single crystalline media for tunable solid-state lasers. These materials behave as promising laser host materials due to their high and continuous transparency in the wide range of the near-IR region. A systematic investigation of these phases is nonetheless hampered because it is impossible to produce large crystals and only in a few cases a pure synthetic product can be achieved. Despite substantial advances in X-ray powder diffraction methods, structure investigation on nanoscale is still challenging, especially when the sample i…
Total oxidation of propane using nanocrystalline cobalt oxide and supported cobalt oxide catalysts
2008
Abstract Supported and unsupported nanocrystalline cobalt oxides have been shown to be extremely efficient catalysts for the total oxidation of propane. Total conversion with a high stability has been achieved at reaction temperatures as low as 250 °C. In the present work, a comparison between the catalytic performance of bulk and alumina-supported nanocrystalline cobalt oxide catalysts has been made. The influence of crystallite size, nature of the support (alpha, gamma and mesoporous alumina) and cobalt loading, has been probed. Unsupported cobalt oxide catalysts were more active than any supported cobalt oxide catalysts. The catalytic activity was mainly dependent on the crystallite size…