Metal oxide nanotubes have become a widely investigated material, more specifically, self-organized titania nanotube arrays synthesized by electrochemical anodization. As a highly investigated material with a wide gamut of applications, the majority of published literature focuses on the solar-based applications of this material. The scope of this review summarizes some of the recent advances made using metal oxide nanotube arrays formed via anodization in solar-based applications. A general methodology for theoretical modeling of titania surfaces in solar applications is also presented.
Me 3 P)AuCtCPh is a molecular compound associated into chains through aurophilic contacts, while its silver analogue exists as the ionic isomer [(Me 3 P) 2 Ag] + [Ag(CtCPh) 2 ] -. Equivalent mixtures of the two compounds (Au:Ag ) 1:1) in dichloromethane yield the ionic mixed-metal compound [(Me 3 P) 2 Ag] + [Au(CtCPh) 2 ] -, which is stable in solution only in the presence of an excess of the Me 3 P ligand. Under these conditions it can be crystallized, and in the crystals the cations and the anions (with idealized D 3d and D 2h symmetry, respectively) are aggregated via heterometallophilic bonding, generating linear -Ag-Au-Ag-Au-chains. The solid was found to be also unstable at room temperature, owing to a rapid loss of four out of six tertiary phosphines, which leads to a product of the composition [(Me 3 P) 2 Ag] + [Ag 2 Au 3 (CtCPh) 6 ] -. By crystal structure analysis, the anion was shown to have three [PhCtCAuCtCPh] -anions associated via two Ag + cations to give a Ag 2 Au 3 core unit of quasi-D 3h symmetry. Structure and bonding in this anion have been analyzed through density functional calculations of the [Ag 2 Au 3 (CtCH) 6 ] -model and shown to be largely ionic in nature. Deviations of the experimental and calculated geometrical details could be traced to the electrostatic field in the crystal. In the unit cell, the cluster anions are associated with the [(Me 3 P) 2 Ag] + cations (of idealized D 3h symmetry) via heterometallophilic contacts in which two of the three gold atoms are involved.
A facile electrochemical technique has been employed to fabricate titania nanotube (T-NT)/cobalt sulfide (CoS) composite electrode for high performance supercapacitor application. The morphology and phase evaluation of the electrode were analyzed using scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) techniques. The pseudocapacitance behavior of the T-NT/CoS composite electrode has been evaluated in four different aqueous electrolytes: KOH, KCl, Na 2 SO 4 and Na 2 SO 3. Cyclic voltammetric studies in aqueous KOH electrolyte indicated that a very high specific capacitance (370 F g-1) can be achieved in this electrolyte together with excellent cycle stability even after 300 consecutive CV cycles. Further, the capacitance behavior of the T-NT/CoS electrode in KCl, Na 2 SO 4 , and Na 2 SO 3 electrolytes exhibited a mixture of electric double layer (EDL) and redoxinduced supercapacitance as displayed in the cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopic (EIS) experiments. It was also observed that the capacitance behavior of the composite material is not greatly dependent on the electrolyte used
The article demonstrates the influence of annealing temperature on the supercapacitance behavior of iron oxide nanotube synthesized on pure iron substrate by electrochemical anodization process. Anodization was performed in an ethylene glycol solution containing 3% H 2 O and 0.5 wt. % NH 4 F. The as-anodized nanotubes were annealed in an ambient atmosphere at various temperatures ranging from 200 to 700ºC for a fixed duration of time (2hrs). The morphology and crystal phases developed after anodization and subsequent annealing processes were examined using field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD) and X-ray photospectroscopy (XPS). Cyclic voltammetry (CV), galvanostatic charge/discharge and electrochemical impedance spectroscopy (EIS) experiments were performed in 1 M Li 2 SO 4 to evaluate the electrochemical capacitance properties of the oxide nanotube electrodes. It was found that the electrode annealed at 300°C exhibited superior electrochemical capacitance compared to the electrodes annealed at other temperatures. The highest specific capacitance achieved after annealing at 300°C was about 314 mF cm-2. The
Using a scalar relativistic all-electron density functional method, we studied uranium(VI) complexation with benzoic acid and its derivatives in aqueous solution as models of uranyl humates. We explored monodentate, bidentate, and chelate coordination of various isomers of methyl and hydroxyl substituted benzoic acid ligands. Monodentate complexes were determined to be energetically preferred as long as entropy effects were neglected. However, bidentate structures were favored at the Gibbs free energy level. Coordination of aromatic carboxylic acids tends to be weaker than that of aliphatic ones, while structural characteristics were determined to be quite similar. Optimized geometries yield uranyl bonds and U-C distances in agreement with EXAFS results for monocarboxylate of benzoate and p-hydroxy benzoate. Average uranyl-oxygen distances to equatorial ligands, U-O(eq), are shorter than in experiment, which is tentatively rationalized by variations in the coordination numbers. As for aliphatic monocarboxylate complexes studied earlier, U-O(eq) values of benzoic acid derivatives do not discriminate mono- and bidentate coordinated species. Structures and energies determined support the interpretation of uranyl humate complexes as bidentate carboxylate species with fivefold coordination of uranyl.
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