Preparation And Study On Gas-Sensing Properties Of Meta-Cresol Purple Composite Film Optical Waveguide Elements

At present, interior and outdoor air pollution is one of the most concerned environmental problems all over the world. With the growth of living standard, life and health is payed greater attention by human beings. In order to effectively detect pollutants, prevent from disasters and ensure sound life, it is of great significance to study a new type of sensor or effective approach of safe, reliable, continuous and rapid on-site detection of trace gases. Optical waveguide(OWG) sensors have a flexible option on sensitive materials and exhibit several merits over other types of sensors, such as the potentials for high sensitivity, fast response, easily microminiaturization, continuously on-line monitoring, anti-electromagnetic interference, and low in production cost, so it has a broad application prospect in the environmental monitoring, biochemical detection, and other fields. OWG sensor technique will play an important role on gas detection applications.The article began by describing the sources and hazards of harmful gases. Common detecting methods of diverse gases and background of sensitive materials selection were made a list. The classification of sensor technology was also introduced. Then we focused on describing the characteristics, classification and working principle of optical waveguide sensors, and reviewed its development. At last we introduced the development history and application of OWG chemical sensors, sensitive film materials and preparation methods of sensing film.In the second chapter, the gas-sensitivity study on meta-cresol purple-polyvinylpyrrolidone(m CP-PVP) composite film based on potassium ion-exchanged glass OWG was introduced. The m CP doped PVP ethanol solution was taken as sensitive reagent, and was fixed on the surface of potassium ion-exchanged glass OWG using a spin-coating method. Then the gas-sensitivity of the as prepared m CP-PVP composite film/potassium ion-exchanged glass OWG sensor to acid and base gases were studied. At last, sensitive mechanism was explained by the change of molecular absorption and optical properties of the sensing film. The result demonstrated the sensor had a good, fast, repeatable response to hydrogen sulfide, sulfur dioxide, ammonia and trimethylamine with a lower concentration of 1×10-10(V/V0, 2.66×10-4 mg/m3), 1×10-10(1.41×10-4 mg/m3), 1×10-10(6.95×10-5 mg/m3) and 1×10-13(2.41×10-7 mg/m3), respectively.On the basis of study described in Chapter 2, the preparation of m CP-PVP composite films was optimized in the third chapter. The p H of m CP-PVP solution was adjusted by buffer solution with certain p H range. The obtained mixed solution was fixed on the surface of potassium ion-exchanged glass OWG with the process of rotating coating. The selectivity of the optimized sensor had obvious improvement after optimizing the p H values of sensing film solution, the amount of m CP and PVP and rotating speed. The as-obtained sensor had a good and repeated response to SO2 with high sensitivity of 1×10-14(1.41×10-8 mg/m3) and short response-recovery time.In the fourth chapter, the gas-sensitivity study on meta-cresol purple-stearic acid(m CP-SA) composite film/potassium ion-exchanged glass OWG was introduced. The m CP doped SA ethanol solution was as sensitive reagent, and then was fixed on the surface of potassium ion-exchanged glass OWG by a spin-coating method. The gas-sensitivity of the OWG sensor was studied with the m CP content and SA doping amount screened and optimized. The sensor had a excellently selective response to NO2 down to 10-11(1.88×10-5 mg/m3) with high sensitivity and rapid response. The sensor will have a better practical value.In the fifth chapter, the gas-sensitivity study on m CP-PVP-SA composite film/potassium ion-exchanged glass OWG was introduced. The m CP-PVP-SA ethanol solution was taken as sensitive reagent, which was fixed on the surface of potassium ion-exchanged glass OWG by a spin-coating method. Then gas-sensitivity of m CP-PVP-SA composite film/potassium ion-exchanged glass OWG sensor was studied. We continue to screen the SA doping amount on the basis of Chapter 2. The result demonstrated that this sensor had a selective response to SO2 below 10-13(1.41×10-7 mg/m3). Even though it had rapid response, its sensitivity is inferior to a certain p H of m CP-PVP sensor.The last part is conclusion, summarizing all the study and experimental results.