Nitrogen oxides sensors

Oda, A., Imanaka, N. and Adachi, G.-Y. (2003) New type of nitrogen oxide sensor with multivalent cation- and anionconducting solid electrolytes. Sens. Actuators B, 93, 229-32. 

Mukundan. R., Teranishi, K., Brosha, E.L, and Garzon, F.H. (2007) Nitrogen oxide sensors based on yttria-stabilized zirconia electrolyte and oxide electrodes. Electrochem. Solid-State Lett., 10 (2), J26-9. 

Ishihara T., Fujita H., Nishiguchi H., and Takita Y, SrSnOj-WOj as capacitive-type nitrogen oxide sensors for monitoring at high temperature. Sens. Actuators B, 65, 319-324, 2000. 

Tamaki J., Fujii T., Fujimori K., Miura N., and Yamazoe N., Application of metal mng-state-carbonate composite to nitrogen oxides sensor operative at elevated temperature. 

Figure 9.54 displays the results obtained using an ECONOX sensor and using a nitrogen oxide sensor, used here for reference. We must also remember that the response of the ECONOX sensor decreases in the presence of nitrogen oxides. 

Lampe U, GerbUnger J, Meixner H (1995b) Nitrogen oxide sensors based on thin films of BaSn03. Sens Actuators B... 

Barsan N, Schweizer-Berberich M, Gopel W (1999) Fundamental and practical aspects in the design of nanoscaled SnOj gas sensors a status report. Fresenius J Anal Chem 365 287-304 Benard S, Retailleau L, Gaillard F, Vernoux P, Giroir-Fendler A (2005) Supported platinum catalysts for nitrogen oxide sensors. Appl Catal B Environ 55 11-21... 

A similar device with Nasicon solid electrolyte Na3Sc(P04)3 is used when analyzing the concentration of nitrogen oxides in air. The electrochemical system in this sensor can be formnlated as... 

The sensor s fnnction rests on the property of lead dioxide to sorb nitrogen oxides (NOJ, forming lead nitrate. In this case the lead nitrate concentration is proportional to the nitrogen oxide concentration in the air. The sorption of the nitrogen oxides is a reversible process The Pb02 is regenerated completely within a few minutes when exposed to clean air (free of nitrogen oxides). 

The electroreduction of some typically inorganic compoimds such as nitrogen oxides is catalysed by the presence of polymeric osmium complexes such as [Os(bipy)2(PVP)2oCl]Cl, where bipy denotes 2,2 -bipyridyl and PVP poly(4-vinylpyridine). This polymer modifies the reduction kinetics of nitrite relative to the reaction at a bare carbon electrode, and provides calibration graphs of slope 0.197 nA with detection limits of 0.1 pg/mL and excellent short-term reproducibility (RSD = 2.15% for n = 20). The sensor performance was found to scarcely change after 3 weeks of use in a flow system into which 240 standards and 30 meat extracts were injected [195]. 

As mentioned earlier, the oxidation of carbon monoxide and hydrocarbons should be achieved simultaneously with the reduction of nitrogen oxides. However, the first reaction needs oxygen in excess, whereas the second one needs a mixture (fuel-oxygen) rich in fuel. The solution was found with the development of an oxygen sensor placed at exhaust emissions, which would set the air-to-fuel ratio at the desired value in real time. So, the combination of electronics and catalysis and the progress in these fields led to better control of the exhaust emissions from automotive vehicles. 

Although the ISEs based on cobyrinates have good selectivity for nitrite over several anions, they also respond to salicylate and thiocyanate. To eliminate this interference, the nitrite-selective electrode based on ionophore 2 was placed behind a microporous gas-permeable membrane (GPM) in a nitrogen oxide gas-sensor mode (75). NOx was generated from nitrite in the sample at pH 1.7 and, after crossing the GPM, was trapped as nitrite by an internal solution that was buffered at pH 5.5 (0.100 M MES-NaOH, pH 5.5, containing 0.100 M NaCl). The internal solution was "sandwiched" between the nitrite-selective electrode and the GPM. 

The conductivity of a generic semiconductor film is likely to be modulated by absorption of a polar species on the film surface. For example, a group at the Weiz-mann Institute has examined GaAs surfaces and found that porphyrin receptors linked to it will attract nitrogen oxide NO, and the binding of NO caused a change in resistance [5]. Other embodiments of GaAs sensors were found to be sensitive to ions in solution [25]. 

The coordinative and/or dissociative adsorption of various probe molecules has been used to characterize the surface properties of Ti02) which finds applications as a catalyst, photocatalyst, and sensor. Among the molecules used as probes, we mention CO (37, 38, 563-576), C02 (563, 565, 577), NO (578,579), water (580,581), pyridine (582,583), ammonia (584,585), alcohols (586, 587), ethers (including perfluoroethers) (588), ozone (589), nitrogen oxide (590), dioxygen (591), formic acid (592-594), benzene (584), benzoic acid (595), and chromyl chloride (596). 

Amperometric gas sensors are - electrochemical cells that produce a - current signal directly related to the concentration of the - analyte by - Faraday s law and the laws of - mass transport. The schematic structure of an amperometric gas sensor is shown in Fig. 1. The earliest example of this kind of sensor is the - Clark sensor for oxygen. Since that time, many different geometries, membranes, and electrodes have been proposed for the quantification of a broad range of analytes, such as CO, nitrogen oxides, H2S, O2, hydrazine, and other vapors. 

Zirconia sensors have been used primarily in the exhaust system of automobiles to control the air-to-fuel ratio for meeting the federal requirements on such noxious gases as carbon monoxide, methane and nitrogen oxides. The applicability of zirconia sensors for this particular application is based on the assumption that, under thermodynamic equilibrium, the partial pressure of oxygen in the exhaust gas depends primarily on the air-to-fuel ratio. To compensate for the fact that in reality equilibrium is not reached, catalytic platinum electrics are incorporated in the zirconia sensor design [Stevens, 1986]. In the zirconia sensor, the outside of the zirconia tube is exposed to the exhaust gas while the inside is exposed to the ambient air as a reference atmosphere. 

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