Use as Gas Sensors

Though they utilized a novel hollow-sphere form of WO3 rather than WO2 72 nanorods, the work of Li s group in researching tungsten oxide as gas sensors can be applied to thenanorodform. Li sporous, hollow spheres were substituted for tungsten oxide polycrystalline films used in the previous studies by Galatsis et al. and Choi et Thus, they overcome the sensitivity and selectivity problems caused by the 

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Montanaro L., Negro A., Pijolat C., Lalauze R., Synthesis and forming of beta alumina to be used as gas sensor, Annales de Chimie [Science des Materiaux] 1995 20 399-402. 

Crown ether-phthalocyanines 118 (n = 0, 1,2) (Scheme 65) were used as gas sensors for N02. They were found to be superior to the previously used materials... 

Thin films, to attain enough sensitivity and response time, of oxide materials normally deposited on a substrate are typically used as gas sensors, owing to their surface conductivity variation following surface chemisorption [183,184], Surface adsorption on a Sn02 film deposited on alumina produces a sensitive and selective H2S gas sensor [185]. In addition, a number of perovskite-type compounds are being used as gas sensor materials because of their thermal and chemical stabilities. BaTi03, for example, is used as sensor for C02 [183],... 

Sensors The ceria NPs could also be used in biosensors as well as the gas sensors. The redox catalytic activity and the semiconductivity of ceria allow it to be used as gas sensors for the reductive and oxidative gases such as CO, NO2,02, and alcohols by the resistivity or catalumines-cence measurements. The noble metals or metal oxides which could activate the catalytic process of ceria could also help to increase the sensitivity of ceria for gas sensing. 

Arakawa, T. Kurachi, H. Shiokawa, J., Physicochemical properties of rare earth perovskite oxides used as gas sensor material, J. Mater. Sci. 1985, 20, 1207-1210... 

APCVD has been used to deposit films of tungsten oxide for use as gas sensors (Ashraf et al., 2007a Pinions et al., 2007) and the gas sensors were shown to give a good response in the presence of ethanol. 

Not long ago,this group first described microelectrochemical devices, which are based on microfabricated arrays of electrodes, connected by electroactive materials. Because the active components of these devices are chemical in nature, many of these devices are chemically sensitive,and comprise a potentially useful class of chemical sensors. Devices showing sensitivity to pH, 02r 2 f and Na" have been demonstrated. These devices are, typically, operated in fluid solution electrolytes. If this class of devices is to be useful as gas sensors, systems which are not dependent on liquid electrolytes need to be developed. We have recently reported solid state microelectrochemical transistors, which replace conventional liquid electrolytes with polymer electrolytes based on polyethyleneoxide (PEG) and polyvinylalcohol (PVA). In this report, we discuss additional progress toward solid-state devices by employing a new polymer ion conductor based on the polyphosphazene comb-polymer, MEEP (shown below). By taking advantage of polymer ion conductors we have developed microelectrochemical devices, where all of the components of the device are confined to a chip. 

Metal porphyrins and phthalocyanines embedded in transparent sol-gel films have been deposited by piezoelectric inkjet printing. Their use as gas sensors was studied (29). 

The electrochemical cell, as shown schematically in Fig. 1, consists of gas-tight ceramic electrolyse in the form of tubes, discs, planar substrates, or thick films which is sandwiched by precious metal like platinum or silver as electrodes. Both electrodes are in close contact with two separate gas compartments. Such cells often modified by other electrode materials like electric conducting oxides (chromites, manganites) are commonly used as gas sensors, fuel cells, and electrolysis cells. Yttria-stabilized zirconia (YSZ Zro.84To.i6< i.92) as oxide ionic conductor is widely used as an electrolyte. 

Table 7.1 Parameters of materials used as gas sensor platforms...

Used as a component in the development of IBM s single-molecule logic switch. Metallated derivatives also And use as gas sensors and in PDT. 

In heterogeneous catalysis, medium- to large-pore carbons with a high total pore volume are preferred in order to increase the contact surface between the reactants and the active sites. Nitrogen-doped CNTs lead to the more active support for gas adsorption. Peng and Cho reported that N-CNTs could be used as gas sensors for CO and water while CNTs are not sensitive to these molecules [99]. 

Electrochemical cells with solid electrolytes are widely used as gas sensors for emission monitoring in exhausts and fermentation plants. As a solid electrolyte gas-tight sintered ceramics in form of tubes, discs, planar substrates or thick films consisting of stabilised zirconia (e.g. YSZ means the most common solid electrolyte yttria-stabilised zirconia) are utilised. With increasing temperature the electrolytical conductivity increases exponentially. 

Chemiresistors have been extensively used as gas sensors. Generally, they are fabricated by deposition of a conducting polymer layer on an insulating substrate usually with gold conductor pads to enable a measurement of the conductivity of the polymer layer. To improve the sensitivity and performance of chemiresistor sensors, an interdigitated electrode stmcture can be utilized. An interdigitated chemiresistor sensor... 

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