Nitrogen dioxide sensor

The miniature fiber optic NO2 sensors based upon dye encapsulation in the silica sol-gel can produce linear and reproducible results87. The nitrogen dioxide sensor based on immobilization of ruthenium complex [Ru(bpy)3]Cl2 demonstrated sensitivity in the hundreds parts per million range with reversibility and rapid response time. 

Banno S., Imanaka N., and Adachi G., Selective nitrogen dioxide sensor based on nickel copper oxide mixed with rare earths. Sens. Actuators B, 24/25, 619-622, 1995. 

By using different membranes, it is possible to obtain potentiometric sensors for gases such as sulfur dioxide or nitrogen dioxide. Such sensors employ similar (acid-base) or other equilibrium processes. These devices, along with their equilibrium processes and internal electrodes, are summarized in Table 6-2. Membrane coverage... 

Other usefiil gas sensors include the potentiometric ammonia (64) or hydrogen cyanide probes (65), and amperometric carbon monoxide (66) and nitrogen dioxide (67) devices. The hydrogen cyanide probe is an example of a modem device that relies on changes in the conductivity of electropolymerized film (polyanihne) in the presence of a given gas. 

Kolesar ES, Wiseman JM. 1991. Selective detection of nitrogen-dioxide and diisopropyl methylphosphonate with an interdigitated gate electrode field-effect transistor (IGEFET). Sensors and Actuators B - Chemical 5(l-4) 37-46. 

Grant S.A., Sateher Jr. J.H., Bettencourt K., Development od sol-gel based fiber optic nitrogen dioxide gas sensors, Sens. Actuat B 2000 69 132-137. 

A semiconductor sensor-based instrument was described for determination of the composition and concentrations of vapors of organic nitro compounds and nitrogen dioxide in the atmosphere. Four organic semiconductor sensors [e.g. aluminum phthalocyanine fluoride (222a)] were tested in conjunction with platinized platinum preconcentrators sensitivity is to ppm levels of nitrobenzene450. 

Each of these considerations must be resolved before a personal monitor can be applied to air pollution research and characterization studies. Some advances have been made for carbon monoxide, volatile organic compounds, acid aerosols, and particulate matter (PM-10 and RSP these represent the masses of all particles collected in samplers with 50% cut sizes of 10 and 25 xm, respectively) and its components (12, 22-31). Each advance is still undergoing development, and further advances can be anticipated for these as well as for other pollutants. The next generation of monitors will probably include devices for some pollutants that incorporate the use of microsensors. Currently, microsensors are being examined for detection of nitrogen dioxide and ozone, but the range of sensors available suggests that they can be used for a number of compounds (10, 32) ... 

Tungsten trioxide thin films activated by gold layers have also been used for NOj. detection.115 This material possesses excellent sensitivity towards nitric oxide and nitrogen dioxide. An automobile exhaust gas NO sensor that uses a gold-platinum alloy electrode has also been reported.116... 

Sensors for nitrogen dioxide detection use a Au/PVC composite prepared by dispersion of a fine gold powder in a highly plasticised PVC matrix containing a hydrophobic electrolyte (Au/PVC electrode)117 which could be used continuously for monitoring the gaseous environment when the nitrogen dioxide content varied only slowly. 

Fig. 4.117. Qualitative do resistance response characteristic at room temperature of a conductive polypyrrole sensorto pulses of amnnonia and nitrogen dioxide (J. J. Miasik, A. Hooper, P. T. Mosely, and B. C. Tofield, Electronically Conducting Polymer Gas Sensors, in Conducting Polymers, Luis Alcacer, ed., Reidel, Dordrecht, The Netherlands, 1987).

Several studies of phthalocyanines in the presence of strong oxidants, such as chlorine, ozone, and nitrogen dioxide, attribute the primary electronic sensor response to the Sc term (2) where the strong chemical oxidant gasses accept an electron as in (3)-(5) [38, 99, 105-125],... 

Since the difference between the minimum and the maximum values of the energy barrier (AE) is lower in the case of W added materials than on pure Sn02, the above result can not be associated with a greater amount of oxygen ions adsorbed which is at the contrary expected to increase AE [14]. In fact, from the Fig. 6b, AE is 0.15 eV in the case of SN-850, 0.13 eV for Wl-850 and finally O.Il eV for W5-850. Therefore the decreased conductance has to be attributed to the increased number of holes in the valence band injected by the acceptor-like W ions. The Sn02 and W-added Sn02 based films were tested as gas sensors towards carbon monoxide and nitrogen dioxide. 

Su P.-G., Wu R.-J., and Nieh F.-R, Detection of nitrogen dioxide using mixed tungsten oxide-based thick film semiconductor sensor, Talanta, 59, 667-672, 2003. 

Another promising example of a metal-based sensor can be seen in the work of Lee and Okura (239) who used entrapped platinum octaethylporphyrin complexes to form photostable devices. In their study, they found by adding the surfactant Triton X-100 to the sol-gel mixture, they could improve homogeneity and phosphorescence of the dye-containing glass. Encapsulated porphyrin molecules have also been used successfully in the sensing of nitrogen dioxide (240) and, as will be discussed below, can be used to sense metal ions. 

Figure 8.16. Electric response of the sensors with different kind of electrodes in the presence of synthetic air, of carbon monoxide (300ppm/air) and nitrogen dioxide (100 ppm/air) at 500°C...

In the present ease we lay out a sensor whieh selects nitrogen dioxide above other gases like carbon monoxide. 

---