Optical sensing elements for nitrogen dioxide (NO2) gas detection, a sol-gel method for making the sensing elements and fiber optic sensors incorporating nitrogen dioxide gas optical sensing elements
First Claim
1. A method of making a nitrogen oxide sensing element comprising:
- incorporating a diazotizing reagent which reacts with nitrous ions to produce a diazo compound and a coupling reagent which couples with the diazo compound to produce an azo dye into a sol; and
allowing the sol to gel;
wherein the gel comprises a microporous optically transparent inroganic matrix comprising immobilized diazotizing reagent and immobilized coupling reagent.
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Abstract
A sensing element, a method of making a sensing element, and a fiber optic sensor incorporating the sensing element are described. The sensor can be used for the quantitative detection of NO2 in a mixture of gases. The sensing element can be made by incorporating a diazotizing reagent which reacts with nitrous ions to produce a diazo compound and a coupling reagent which couples with the diazo compound to produce an azo dye into a sol and allowing the sol to form an optically transparent gel. The sensing element changes color in the presence of NO2 gas. The temporal response of the absorption spectrum at various NO2 concentrations has also been recorded and analyzed. Sensors having different design configurations are described. The sensing element can detect NO2 gas at levels of parts per billion.
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Citations
46 Claims
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1. A method of making a nitrogen oxide sensing element comprising:
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incorporating a diazotizing reagent which reacts with nitrous ions to produce a diazo compound and a coupling reagent which couples with the diazo compound to produce an azo dye into a sol; and
allowing the sol to gel;
wherein the gel comprises a microporous optically transparent inroganic matrix comprising immobilized diazotizing reagent and immobilized coupling reagent. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34)
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35. A nitrogen oxide sensing element comprising:
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a microporous matrix of an optically transparent inorganic compound;
a diazotizing reagent which reacts with nitrous ions to produce a diazo compound; and
a coupling reagent which couples with the diazo compound to produce an azo dye;
wherein the diazotizing reagent and the coupling reagent are immobilized in the microporous matrix. - View Dependent Claims (36, 37, 38, 39, 40)
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41. A nitrogen oxide sensor comprising:
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a film sensing element comprising a microporous matrix of an optically transparent material, a diazotizing reagent which reacts with nitrous ions to produce a diazo compound and a coupling reagent which couples with the diazo compound to produce an azo dye;
a light source; and
an optical detector;
wherein the sensing element is coupled to the light source by one or more transmitting optical fibers and wherein the sensing element is coupled to the detector by one or more receiving optical fibers such that light from the light source is transmitted through the one or more transmitting optical fibers and impinges on the sensing element and light impinging on the sensing element is transmitted through the one or more receiving optical fibers to the detector; and
wherein ends of the transmitting and receiving fibers adjacent the sensing element are positioned on the same side of the film sensing element. - View Dependent Claims (42, 43, 44, 45, 46)
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Specification