Synthesis of Porous Transition Metal Oxides by the Salt-Gel Method

1994 ◽  
Vol 371 ◽  
Author(s):  
Andreas Stein ◽  
Mark Fendorf ◽  
Thomas P. Jarvie ◽  
Karl T. Mueller ◽  
Maurie E. Garcia ◽  
...  
Keyword(s):  
Transition Metal ◽  
Metal Oxides ◽  
Transition Metal Oxides ◽  
Molecular Sieves ◽  
Double Resonance ◽  
Acid Extraction ◽  
Framework Materials ◽  
Periodic Arrays ◽  
Surface Areas ◽  
Transition Metal Silicates

AbstractComposites of surfactants with certain transition metal oxides can be arranged into periodic arrays with giant tunnel structures. Transmission electron micrographs of these structures resemble images of mesoporous silicate molecular sieves synthesized in the presence of surfactants. However, data in this study lead to the conclusion that Keggin-ions of the type (H2W12O40)6- are formed during the hydrothermal synthesis of a cetyltrimethylammonium/tungstate composite. These cluster anions are not connected to each other. Removal of the organic template therefore results in the collapse of the tunnel structures.A strategy has been developed which uses pre-arranged surfactant-salt structures as precursors for microporous and mesoporous framework materials. Transition metal silicates with long-range structural order have been synthesized by reacting surfactant salts of niobotungstate clusters with tetraethylorthosilicate to form a salt-gel. Infrared and solid-state NMR double resonance spectra indicate that, in addition to linkages between silicate tetrahedra, niobium-oxygen-silicon linkages have been formed in this reaction. Removal of the cationic surfactants by acid-extraction has resulted in porous structures with surface areas up to 265 m2/g.

scholarly journals Significantly enhancement of sunlight photocatalytic performance of ZnO by doping with transition metal oxides

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Alfonso E. Ramírez ◽  
Marly Montero-Muñoz ◽  
Lizbeth L. López ◽  
J. E. Ramos-Ibarra ◽  
Jose A. H. Coaquira ◽  
...  
Keyword(s):  
Photocatalytic Activity ◽  
Transition Metal ◽  
Metal Oxides ◽  
Transition Metal Oxides ◽  
High Performance ◽  
Photocatalytic Performance ◽  
Adsorption Sites ◽  
Surface Areas ◽  
Transmission Electron ◽  
Materials Used

AbstractIn this study we report, the synthesis of ZnO and its doping with Transition Metal Oxides -TMO-, such as Cr2O3, MnO2, FeO, CoO, NiO, Cu2O and CuO. Various characterization techniques were employed to investigate the structural properties. The X-ray diffraction (XRD) data and Rietveld refinement confirmed the presence of TMO phases and that the ZnO structure was not affected by the doping with TMO which was corroborated using transmission Electron microscopy (TEM). Surface areas were low due to blockage of adsorption sites by particle aggregation. TMO doping concentration in the range of 3.7–5.1% was important to calculate the catalytic activity. The UV–Visible spectra showed the variation in the band gap of TMO/ZnO ranging from 3.45 to 2.46 eV. The surface catalyzed decomposition of H2O2 was used as the model reaction to examine the photocatalytic activity following the oxygen production and the systems were compared to bulk ZnO and commercial TiO2-degussa (Aeroxyde-P25). The results indicate that the introduction of TMO species increase significantly the photocatalytic activity. The sunlight photocatalytic performance in ZnO-doped was greater than bulk-ZnO and in the case of MnO2, CoO, Cu2O and CuO surpasses TiO2 (P25-Degussa). This report opens up a new pathway to the design of high-performance materials used in photocatalytic degradation under visible light irradiation.

HREM Study of electron-induced surface radiation damage in ReO3

1991 ◽  
Vol 49 ◽  
pp. 636-637
Author(s):  
R. Ai ◽  
H.-J. Fan ◽  
L. D. Marks
Keyword(s):  
Transition Metal ◽  
Metal Ions ◽  
Metal Oxides ◽  
Electron Irradiation ◽  
Transition Metal Oxides ◽  
Carbon Film ◽  
Transition Metal Ions ◽  
Surface Radiation ◽  
Valence Transition ◽  
Electron Microscopes

It has been known for a long time that electron irradiation induces damage in maximal valence transition metal oxides such as TiO2, V2O5, and WO3, of which transition metal ions have an empty d-shell. This type of damage is excited by electronic transition and can be explained by the Knoteck-Feibelman mechanism (K-F mechanism). Although the K-F mechanism predicts that no damage should occur in transition metal oxides of which the transition metal ions have a partially filled d-shell, namely submaximal valence transition metal oxides, our recent study on ReO3 shows that submaximal valence transition metal oxides undergo damage during electron irradiation.ReO3 has a nearly cubic structure and contains a single unit in its cell: a = 3.73 Å, and α = 89°34'. TEM specimens were prepared by depositing dry powders onto a holey carbon film supported on a copper grid. Specimens were examined in Hitachi H-9000 and UHV H-9000 electron microscopes both operated at 300 keV accelerating voltage. The electron beam flux was maintained at about 10 A/cm2 during the observation.

Problems with oxygen analysis in the system MgO-Al2O3-SiO2 with the electron microprobe

1992 ◽  
Vol 50 (2) ◽  
pp. 1624-1625
Author(s):  
Michel Fialin ◽  
Guy Rémond
Keyword(s):  
Transition Metal ◽  
Metal Oxides ◽  
Transition Metal Oxides ◽  
Electrostatic Charge ◽  
Carbon Layer ◽  
Sample Holder ◽  
Rock Matrix ◽  
Electrical Discharges ◽  
Thin Carbon ◽  
Beam Instabilities

Oxygen-bearing minerals are generally strong insulators (e.g. silicates), or if not (e.g. transition metal oxides), they are included within a rock matrix which electrically isolates them from the sample holder contacts. In this respect, a thin carbon layer (150 Å in our laboratory) is evaporated on the sections in order to restore the conductivity. For silicates, overestimated oxygen concentrations are usually noted when transition metal oxides are used as standards. These trends corroborate the results of Bastin and Heijligers on MgO, Al2O3 and SiO2. According to our experiments, these errors are independent of the accelerating voltage used (fig.l).Owing to the low density of preexisting defects within the Al2O3 single-crystal, no significant charge buildup occurs under irradiation at low accelerating voltage (< 10keV). As a consequence, neither beam instabilities, due to electrical discharges within the excited volume, nor losses of energy for beam electrons before striking the sample, due to the presence of the electrostatic charge-induced potential, are noted : measurements from both coated and uncoated samples give comparable results which demonstrates that the carbon coating is not the cause of the observed errors.

scholarly journals Electronic Phenomena of Transition Metal Oxides

Crystals ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 256
Author(s):  
Christian Rodenbücher ◽  
Kristof Szot
Keyword(s):  
Solid State ◽  
Transition Metal ◽  
Metal Oxides ◽  
Real World ◽  
Transition Metal Oxides ◽  
Major Research ◽  
Research Fields ◽  
Real World Applications

Transition metal oxides with ABO3 or BO2 structures have become one of the major research fields in solid state science, as they exhibit an impressive variety of unusual and exotic phenomena with potential for their exploitation in real-world applications [...]

Recent advances of layered-transition metal oxides for energy-related applications

2021 ◽  
Vol 36 ◽  
pp. 514-550
Author(s):  
Zhihao Lei ◽  
Jang Mee Lee ◽  
Gurwinder Singh ◽  
C.I. Sathish ◽  
Xueze Chu ◽  
...  
Keyword(s):  
Transition Metal ◽  
Metal Oxides ◽  
Transition Metal Oxides ◽  
Recent Advances ◽  
Layered Transition Metal
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