| With the rapid development of national economy,there are more and more environmental pollution,among which the pollution of toxic and harmful gases to human living space is more prominent.Therefore,it is urgent to develop low concentration chemical sensors to detect harmful environmental pollutants.Porphyrin is a kind of compounds with macrocyclic conjugated structure.Because of its high sensitivity and selectivity to specific gases at room temperature,it was widely used in organic gas sensing materials in recent years.Titanium dioxide(Ti O2)and lithium iron phosphate(Li Fe PO4)are widely used in the field of sensors because of their excellent chemical thermal stability,simple preparation,non-toxic and high refractive index.In this paper,tetra-p-hydroxyphenyl porphyrin(THPP)is used as the main sensitive material,and Ti O2and Li Fe PO4with high refractive index are used to prepare the composite optical waveguide(OWG)sensor with higher sensitivity.The gas sensing performance and gas sensing mechanism were tested and discussed.The first part of this paper mainly introduces the air pollution and current situation,the classification of pollutants,the harm of acid gas and volatile organic compounds;The definition,composition and classification of sensors,the classification and application of sensitive materials were introduced;The structure,principle and application of optical waveguide sensor were summarized.In the second chapter,the THPP film/K+-exchanged glass optical waveguide(OWG)element was prepared by spin coating on the surface of K+-exchanged glass OWG with tetra-p-hydroxyphenyl porphyrin as sensitive material.The absorbance changes of the film before and after contacting with the measured gas were analyzed by Uv-vis spectrophotometer,and the optical waveguide test light source was selected.The surface morphology of the films was observed by SEM,and the gas sensing properties of the films to different gases were tested at room temperature.The experimental results show that the films show good selective response to NO2in SO2,CO2,NO2and HCl gases.The preparation conditions of the sensor were optimized;The detected NO2concentration range is(1×10-4-1×10-8)volume ratio,The response and recovery time of 1×10-6volume ratio NO2were 1 s and 3 s,respectively.Finally,the gas sensing mechanism was discussed by analyzing the surface morphology(SEM)and infrared spectroscopy(FT-IR).In the third chapter,the OWG element of alkaline THPP film/K+-exchanged glass was developed for the purpose of improving the sensitivity of the element to acid gases,because the THPP film/K+-exchanged glass OWG element has some response to other acid gases except NO2.The gas sensitivity of alkaline THPP-OWG to five kinds of acid gases(NO2,SO2,CO2,H2S and HCl)were tested.The experimental results show that when the concentration of the measured gas is high(1×10-3),the output light intensity rapidly decreased and did not recover,and the baseline can only be recovered by saturated NH3steam.When the concentration of the measured gas is low(1×10-4),the sensitivity of the sensitive elements to SO2and H2S is higher among the five kinds of acid gases;The detectable concentration ranges of SO2and H2S are(1×10-3-1×10-7)volume ratio and(1×10-3-5×10-6)volume ratio respectively.Finally,the gas sensing mechanism was discussed by analyzing the surface morphology(SEM)and FT-IR after the film contacted with the measured gas.In the forth chapter,OWG sensor based on composite film has higher sensitivity than K+-exchanged glass OWG sensor,and has greater potential in harmful gas detection.In this chapter,Ti O2sol was prepared by sol-gel method.A new THPP-bromine cresol purple(BCP)/Ti O2composite membrane OWG sensor(THPP-BCP/Ti O2OWG)was developed and characterized by Uv-vis,FT-IR and atomic force microscopy(AFM).The results of OWG test show that the response of THPP-BCP/Ti O2composite film OWG sensor to VOCs is 3?4 times higher than that of single THPP-OWG sensor.The THPP-BCP/Ti O2composite film OWG sensor has good selectivity and high sensitivity to EDA gas at room temperature,and the detectable concentration ranges of EDA is(1×10-3-1×10-9)volume ratio;for 1×10-6volume ratio EDA,the response and recovery time were 1 s and 3 s,respectively.Finally,the absorption spectra of THPP solution,BCP solution,THPP-BCP film,Ti O2film and THPP-BCP/Ti O2composite film before and after contact with EDA were analyzed by Uv-vis spectrophotometer,and the gas sensing mechanism was discussed.In the fifth chapter,the fabrication and gas sensing properties of THPP/Li Fe PO4strip film OWG were introduced.Firstly,Li Fe PO4was synthesized by hydrothermal method,and then Li Fe PO4and THPP were ultrasonically dispersed in SDBS.THPP/Li Fe PO4strip film/tin doped OWG sensor was prepared by spin coating method,and the gases such as amine,benzene,HCl and H2S were tested.The results show that the sensor has a good selective response to H2S,and the detectable concentration ranges are(1×10-3-1×10-7)volume ratio,the response and recovery time were 1 s and 2 s respectively.Finally,the infrared spectrum of THPP/Li Fe PO4thin film in contact with H2S was analyzed by infrared spectroscopy,and the gas sensing mechanism was discussed. |
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