| Research into the design,fabrication,and performance of optical waveguide(OWG)sensors is of great significance for the development of both materials and physical chemistry.Optical waveguide sensor has the advantages of simple preparation,fast response and high sensitivity;consequently,they have great gas-detection prospects.And the sensor performance is closely related to the characteristics of the sensing materials.In this regard,porphyrins have attracted much attention as gas-sensing materials due to their good chemical/thermal stabilities and optical properties,electron-transport performance,and modifiabilities.As the sensing material,porphyrin can improve the selectivity of a sensor,and the selectivity of a metalloporphyrin sensor is determined by the central metal ion.Importantly,the optical properties of porphyrins changes when it interact with the measured gas.Changes in the optical properties of the sensing film of an OWG gas sensor in response to interactions between the film and gas molecules affect the intensity of the output light and is an important feature of such a sensor.With this in mind,in this study,we combined the advantages of porphyrins and metal porphyrins with the characteristics of an OWG sensor to develop highly selective and highly sensitive gas-sensing elements.Specifically:(1)We prepared OWG gas sensor using porphyrin solutions of varying pH,which led to the highly sensitive and highly selective detection of gaseous ethanediamine(EDA)and sulfides(H2S,SO2).5,10,15,20-Tetra(4-methoxyphenyl)porphyrin(TMP)was used as the sensing material and a K+-ion exchanged glass OWG was employed as sensing base.TMP film/K+-ion exchanged glass OWG sensors were prepared by the spin-coating method,the gas sensitivity of each prepared OWG sensing element was studied,and the effect of the pH of the TMP solution on the gas-sensitivity of the OWG sensor was investigated.The experimental results reveal that the sensor prepared using a pH=1.00 of TMP solution is very responsive to EDA gas,with a signal intensity((?)I)of48,and corresponding response and recovery times toward to EDA gas with volume ratio(V/V0)of 1×10-6are 13 s and 38 s,respectively.The relative standard deviation of the output light intensity isą2.84.The signal to noise ratio is 5.6.The sensor prepared using the original solution exhibited an excellent response toward sulfide gases(H2S,SO2)and detected them at the concentration of 1×10-6(V/V0).Hence,these sensing devices can potentially be used to food quality testing and for environmental-monitoring purposes.(2)The influence of the preparing method and the guiding layer structure on OWG sensor performance was also studied.The ZnO precursor sol was fixed on the K+-ion exchanged glass OWG surface by the pulling method to prepare a ZnO film/K+-ion exchanged glass composite optical waveguide(COWG)layer.The surface of the COWG was coated with the TMP film using the spin-coating or immersion method to develop the COWG sensor,and used for the detection of amine,benzene and acidic gases at room temperature.And the gas sensitivities of the COWG sensors prepared by the two methods were compared.Which revealed that the TMP film/ZnO film COWG sensor prepared by the spin-coating method was exhibited highly sensitivity to EDA gas,and can detect the EDA gas with the concentration of 1×10-8(V/V0).The TMP-adsorbed ZnO film COWG sensor prepared by the immersion method was highly sensitive to the sulfides gases(H2S,SO2),detecting them at a concentration of 1×10-10(V/V0).The high sensitivity,room-temperature operability,good selectivity,and reproducibility of the sensor make it a promising candidate for industrial use and environmental-monitoring applications.(3)We also studied the gas sensitivity of the OWG sensor prepared by TMP-ZnO composite material.The TMP-ZnO film OWG sensor was developed by fixing the TMP-ZnO composite material on the surface of K+-ion exchanged glass OWG by spin coating method,and used for the detection of volatile organic gases and acid gases.The influence of the mixing of the TMP and ZnO on the gas sensitivity of the sensing element was discussed.The TMP-ZnO film OWG sensor exhibits a good reversible response to H2S gas and is able to detect H2S gas at a concentration of 1×10-7(V/V0).The TMP-ZnO film OWG sensor is more sensitive to H2S gas than the TMP film OWG sensor.(4)The selectivity of a metalloporphyrin sensor depends on the central metal ion.In this paper,we also detail our study into the gas sensitivities of metalloporphyrin film OWG sensor.The experimental results showed that the Zn TMP film OWG sensor exhibits a good selective response to SO2gas and can detect this gas at a concentration of 1×10-6(V/V0).The Cu TMP film OWG sensor exhibits good selective responses to both gaseous styrene and EDA,and can detected them at a concentration of 1×10-6(V/V0)and 1×10-8(V/V0),respectively.The Ni TMP film and Co TMP film OWG sensors shows good sensitivities to amines;the former detected EDA at a concentration of 1×10-6(V/V0),while the latter clearly responded to 1×10-5(V/V0)of methylamine.The Fe TMP film OWG sensor exhibited large responses to HCl and H2S gases,which were both detected at a concentration of 1×10-6(V/V0). |
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