Design And Synthesis Of New Type Of Sensitive Material And Its Application In Environmental Field

Sensor, a detection device, can feel the information and convert it into electric signals according to certain rules or other desired form, which has been applied into the various fields of industrial automation, medical diagnostics, agriculture, aerospace etc. According to the functions, the sensors can be divided into:photosensitive sensor, gas sensor, humidity sensor, force-sensitive sensor, sound-sensitive sensor. The core of sensor is sensitive material. Among them, the sensitive materials of gas sensors are mainly semiconductor metal oxides, which are easy to design with low cost, and rapid to detect, but they often have poor selectivity, which need to be optimized. The main sensitive materials of humidity sensors are organic polymers, which have good conductivity, structural diversity and easy to test at room temperature. However, they often have poor long-term stability, which also need optimization. Among the approaches to improve the sensing properties of sensitive materials, no matter gas sensitive merials or humidity sensitive materials, to prepare composite materials is proved to be an effective way and has important practical significance to improve the performance of sensitive materials. Focusing on the problems that gas and humidity sensitive materials have, two types of composites have been prepared in this thesis respectively, which are the chlorohydrocarbon sensitive material of ZnO/CuO/AlO3 and the humidity sensitive material of CdS/PANI. In the gas sensing part, the precursor has been synthesized by hydrothermal method and calcined at different temperatures to form a composite metal oxide ZnO/CuO/Al2O3, and its gas sensing performance to low concentrations of chlorohydrocarbon has been studied. Take chloroform as an objective gas, the gas response of composite material to chloroform decreases along with the calcination temperature increasing. It shows that the composite with the three oxides of Zn, Cu and Al together has the best gas response to chloroform, and the percentage of Cu highly affects the gas sensing behavior. At the optimum operating temperature of 200℃, ZnCuo.7Alo.6-500 can detect low concentrations of chloroform even as low as 1 ppm, and shows gas response value as 8.5 to 50 ppm chloroform. The composite also has good reproducibility and selectivity regarding to its gas sensing properties. In the humidity sensing part, polyaniline (PANI) has been cointroduced with the sodium dodecyl sulfate into the interlamination of CdAl layered double metal hydroxide. The obtained CdAl-LDH/PANI has been vulcanized in H2S ambient to get CdS/PANI composite. The humidity sensing performance indicates that CdAl-LDH/PANI has a good linear relationship between the humidity responses and the relative humidity. It also shows stable sensing property and good stability within the range of 11% RH to 95% RH. After sulfidation, CdS/PANI has a stable recirculation curve from 11% RH to 95% RH, the impedance reduces four orders of magnitude and its response time is about 2 s. Therefore, we concluded that the confinement effect of layers and the presence of the semiconductor collaboratively improve the humidity sensing of polyaniline.