An active core fiber optic sensor for detecting trace H2S at high temperature using a cadmium oxide doped porous silica optical fiber as a transducer

An active core fiber optic sensor has been developed for detecting trace H2S in high-temperature gas samples. This sensor uses a cadmium oxide doped porous silica optical fiber prepared with a sol–gel process as a transducer. When this porous silica optical fiber was exposed to a gas sample at high temperatures, trace H2S in the sample diffuse into the porous fiber, and react with the doped cadmium oxide to form cadmium sulfide. The optical properties of this formed compound inside the porous silica optical fiber was investigated with fiber optic spectrometric methods. It was found that cadmium sulfide formed inside the porous silica optical fiber absorbs UV light with peak absorption wavelength at around 370 nm. This absorption signal was observable at a high temperature (450 °C). The formed CdS inside the fiber after H2S exposure emits strong fluorescence at room temperature with peak emission wavelength at around 500 nm. However, this fluorescence signal was quenched at the high temperature (450 °C), and the fluorescence emission property can only be used for detecting trace H2S at low temperature region. The UV absorption based sensor has been calibrated for detecting trace H2S in a nitrogen gas sample, and a linear calibration curve was obtained. This sensor can be used for detecting trace H2S in a high temperature gas sample down to sub-ppm level. Matrix gas components of gasification-derived fuel gas, such as H2, CH4 and CO, were found not interfering with the sensor for detecting H2S. This sensor is expected having the potential of application for monitoring the process of cleaning fossil fuel derived fuel gas.