Gold oxides, structure

Figure 9.6 Activity for CO oxidation at room temperature as a function of gold coverage on an Mo(l 12)—(8 x 2)-TiOx surface. The CO 02 ratio was 2 1 and the total pressure 5 Torr. Two discrete gold structures were investigated, (lxl) and (1 x 3). The initial turn over frequencies (TOF) over the (1 x 1) gold monolayer structure were significantly lower than that for the (1 x 3) bilayer structure. (Reproduced from Ref. 20).

According to the presented model of oxides formation on Au, the outer surface of the thick oxide film exposed to the solution is either AU2O3 or Au(OH)3. The type of oxide determines the surface electronic structure and electrocatalytic properties. Electrocatalytic properties of gold oxide-covered electrodes have been discussed by Burke and Nugent [366, 368]. 

An example of how gold oxidation state can control the structure of the product formed has been provided recently3,10 when haloallenyl ketones were used in gold-catalysed cyclo-isomerisations to give furans (Scheme 12.2) ... 

Davenport et al. [14] have shown that a worm-like structure of gold oxide appears on a crystalline gold surface oxidized electrochemically. By comparing in-situ STM images with electrochemical data it was evident that monolayers of gold oxide were formed at anodic potentials and that a slow reduction of the gold oxide at cathodic potentials recovered the bare surface. The gold surface, however, is not oxidized solely by electrochemical methods. 

Aqua regia literally royal water , so called because it will dissolve gold a mixture of three parts concentrated hydrochloric acid to one part concentrated nitric acid Corundum structure a-aluminum oxide structure Electrochemical oxidation oxidation of a solute by passing a direct electrical current through its solution (e.g. chlorine is produced industrially by the electrochemical oxidation of the chloride ion)... 

The resistance of a tin oxide gas sensor consists of bulk resistance, surface resistance and contact resistance. The reduction of contact resistance is useful for improving the properties of oxide semiconductor gas sensors. An ohmic contact between the electrode and sensing material can reduce the contact resistance. Zhou et al. compared conventional tin dioxide-gold electrode structures with devices in which an n+ layer was introduced between the sensor and electrode. The use of the metal-n+-n contact not only improved the sensitivity of the sensor to alcohol, but also the sensor selectivity to other gases did not change with the addition of an n+ layer. 

The design of subtle specific methods for depositing metal NPs, e.g. [144,145] is another way to control the location of the metal deposit within the CP layer. One proposed approach involves the deposition of a thin, sacrificial Au layer on a Pt substrate, electropolymerization of PANI on the Au-plated substrate, gold oxidation in chloride solution, and finally reduction of the AuCU eomplexes entrapped in the PANI structure. Thus gold/ polyaniline free-standing eomposite films are produced [144,145]. 

Paulik, M. G., P. A. Brooksby, A. D. Abell, and A. J. Downard. Grafting aryl diazonium cations to polycrystalline gold Insights into film structure using gold oxide reduction, redox probe electrochemistry, and contact angle behavior. J. Phys. Chem. C 111, 2007 7808-7815. 

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