Gold catalysts sensors

Titanium dioxide supported gold catalysts exhibit excellent activity for CO oxidation even at temperatures as low as 90 K [1]. The key is the high dispersion of the nanostructured gold particles over the semiconducting Ti02 support. The potential applications of ambient temperature CO oxidation catalysts include air purifier, gas sensor and fuel cell [2]. This work investigates the effects of ozone pretreatment on the performance of Au/Ti02 for CO oxidation. 

It has been reported that cross-metathesis reactions can be performed on olefins using nanoparticulate gold catalysts [579]. The introduction of various organic functional groups onto organic thin films is a first step in their application in sensors, catalysis and nanotechnology in general. 

The oxidation of carbon monoxide at around room temperature is the most famous reaction known for gold catalysts. Haruta s group discovered in 1987 [1, 2] that gold is a unique catalyst for this reaction when gold metal particles are smaller than 5 nm and supported on oxides. Since then, extensive and intensive fundamental works have been published, and expanding new applications, from air purification (gas masks, gas sensors, indoor air quality control) to hydrogen purification for fuel cells (PROX, preferential selective oxidation of CO in the presence of Hj) have been developed. 

It is well established, that the poor selectivity of tin-oxide sensors can partly be overcome by adding catalysts to the sensitive layer. Most common additives are noble metals like gold (Au), platinum (Pt) or palladium (Pd). They can be mixed with the tin oxide during paste formation before deposition. The influence of dopants on the gas sensor response is still subject to debates. The two most established mechanisms are the spill-over and the Fermi-level mechanism [82]. 

SOD-modified sensors also were demonstrated to respond to superoxide addition. Using either 3-mercaptopropionic acid [68] or cysteine [70] as a promoter on Au-electrodes superoxide sensors could be constructed where FeSOD and CuZnSOD in direct contact to the electrode acts as catalyst for the highly specific dismutation of O2 to O2 and H2O2. Either Fe or Cu of SOD are oxidized and reduced (Fe /Fe Cu°/Cu ) at the modified gold electrodes. Both, anodic and cathodic peak currents increase in the presence of O2. At a potential of 300 or- 200 mV O2 -generation could be recognized with detection limits of 5 and 6 nM, respectively [70]. 

Single-layer zinc-phosphate zeolite crystals were grown with more than 90% of their (111) faces oriented to a gold-coated silicon surface. Sudi oriented zeolite films might find application as membrane catalysts or as specific chemical sensors [66]. 

Metallic nanorods are highly interesting materials from many points of view as elements in future nanoscale electronic circuits as sensors as catalysts as optical elements in future nanoscale optical devices. Gold and silver nanorods have distinct visible absorption and scattering spectra that are tunable with aspect ratio. Many workers have developed wet synthetic routes to these nanomaterials, with control of aspect ratio a key improvement compared to the synthesis of simple nanospheres. Another key area for which improvements need to be made is the understanding of the atomic arrangements of the different faces of crystalline... 

Another drawback in electrochemical sensors is the long-term drift, which is sometimes related to the instability of the materials working at high temperatures. Some recent works propose the use of dispersed nanoparticles on the surface, such as platinum or gold, in order to act as a catalyst in the reduction-oxidation reaction, leading to both an increase in sensitivity and a reduction in the operating temperature (Plashnitsa et /., 2009). 

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