| With the rapid progress of modern chemical industry and other industrial sectors,Types and numbers of gases with flammable, explosive and hazardous for humans areincreasing daily. If they leak into the air, it will pollute the environment and affect theecological balance, or even explosions, fires, poisoning and other severe accidents.Therefore, there is an urgent need for research and development of detection methodson a variety of hazardous and toxic gases in the environment. Optical waveguide(OWG) chemical sensor has high sensitivity, fast response, easy to operate at roomtemperature and so on, it was not only widely applied in the industrial production, thefield of chemical and biological monitoring, in particular, but also occupied anincreasingly important role in the detection of harmful gases.As a sensitive part of the optical waveguide chemical sensor, the sensitivematerial directly affect sensing properties of the sensor, through the selection ofappropriate sensitive material, making the sensitive characteristics of the opticalwaveguide chemical sensors at best. In this paper, combining with unique propertiesof the organic sensitive materials and polymer materials and the superior features ofoptical waveguide chemical sensors, doped with stearic acid complexes as a sensitivematerials, and the gas sensing response of these sensitive materials to volatile organicvapors and acid gases was studied by use of optical waveguide detection system. Thepresent paper is composed by following several parts:The first chapter is part of introduction. In this part, the optical chemical sensorsand its classification were simply described. The characteristics and the developmentstatus of optical waveguide chemical sensors, the OWG's sensing principle(evanescent wave sensing principle), its classification and application, Types ofsensitive materials and application in gas detection, and glass OWG (K+-ionexchanged glass OWG) fabrication techniques were mainly introduced. At last, thetopic sources and contents of this study work were put forward. The second chapter is about the gas sensitivity study of PVP-stearic acidcomposite film/K+-ion exchanged glass optical waveguide sensor for volatile organicvapors. Stearic acid complex solution mixed with polyvinyl pyrrolidone (PVP) as asensitive reagent, PVP-stearic acid composite films on the surface of K+-ionexchanged glass optical waveguide were prepared by spin coated method, developedPVP-stearic acid composite film/K+-ion exchanged glass optical waveguide sensor,and carried on the detection of volatile organic vapors, the selective sensingmechanism was briefly explained by changes of organic vapor molar refractive index.The results showed that the sensor has high sensitivity towards xylene and styrenevapors, and fast response, good reversibility, it can detect1×10-6(volume fraction) ofxylene (4.41mg/m3) and styrene (4.33mg/m3)vapors at room temperature.The third chapter is about the research of gas sensing properties of theazobenzene-stearic acid composite film/K+-ion exchanged glass optical waveguidesensor for volatile organic vapors. Azobenzene doping stearic acid composite films assensitive reagents, by filtering out the best rotational speed, and changing the dopingquantity of azobenzene, developed the five different doping amounts of azobenzene-stearic acid composite films/K+-exchanged glass optical waveguide sensors,respectively. Among them, doped with0.032%azobenzene-stearic acid compositefilm/K+-exchanged glass optical waveguide sensor had high sensitivity and bestselectivity, and good reversible response to styrene vapor. The research resultsindicated that the sensor was able to detect1×10-8(0.043mg/m3) of styrene vaporand1×10-7(0.44mg/m3) of xylene vapor.The fourth chapter is methylene blue-stearic acid composite film/K+-exchangedglass optical waveguide sensor and its gas sensitivity. In this chapter, methylene blue(MB) was selected as dopant, doped with different amount of MB-stearic acidcomposite films/K+-exchanged glass optical waveguide sensors were fabricated byspin coated method, the optimal amount of doping is determined through a large number of experiments, detection for styrene, chlorobenzene, toluene, HCl, and NO2was carried out seperately, and sensitive mechanism was also discussed. Theexperimental results showed that the sensor has the good selectivity to styrene,chlorobenzene, toluene, HCl and NO2gases, minimum volume concentrationresponse into1×10-7(0.43mg/m3),1×10-6(4.65mg/m3),1×10-5(38.2mg/m3),1×10-8(0.015mg/m3),1×10-6(1.91mg/m3), respectively.The fifth chapter is cresol red-stearic acid composite film/K+-exchanged glassoptical waveguide sensor and its gas sensitive study. Doped with different content ofcresol red (CR)-stearic acid composite films as a sensitive reagents, immobilized onthe surface of K+-ion exchanged glass optical waveguide, CR-stearic acid compositefilm/K+-exchanged glass optical waveguide sensors were fabricated by spin coatedmethod. In this chapter, doped with0.063%CR-stearic acid composite film/K+-exchanged glass optical waveguide sensor was selected by enormous experimentation,and volatile organic vapor and acid gases were detected, the sensing mechanism ofsensor was discussed. The results showed that the sensor had high sensitivity (it candetect lower than1×10-10(0.14μg/m3) of H2S gas), fast response, good repeatability.The sensor also had response to xylene vapor, it was able to detect the volumefraction of1×10-6(4.41mg/m3) xylene vapor.The sixth chapter is the concluding part, a summary of the main content of ourresearch study. |
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