| In this paper, considerable efforts have been centered on the development of high-performance gas sensors. Based on the current research background and development situation of semiconductor type gas sensors, systematical research works have been carried out in terms of optimization of oxide semiconductor structure, modification of dopant and construction of heterostructures by following the research routes of designing sensing materials, characterizing their structures and performances as well as exploring the corresponding sensing mechanism. First of all, two kinds of single metal oxide, In2O3 hierarchical structure and Zn O core-shell structure were prepared by microwave hydrothermal method and their structure-dependent gas-sensing properties were discussed. Then, the impacts of Au nanoparticles on the sensing properties of single metal oxide Zn O were studied through the modifications of noble metal. On this basis, two kinds of noble metal@semiconductor heterostructures including Au@Zn O and Au@In2O3 were synthesized by template method, and their gas sensing properties were investigated. Finally, the Zn O/Zn Fe2O4 composite was constructed and a comparative sensing investigation between the as-prepared Zn O/Zn Fe2O4 composite and its individual components was investigated. The specific research content of current paper is given below:1. In order to improve the receptor function, transducer function and utility efficiency of oxide semiconductor, we constructed In2O3 hierarchical structures and Zn O core-shell structures and their responses towards NO2 and ethanol were significantly enhanced. The microwave hydrothermal method was employed for the preparation of bundle-like In2O3 with regular and porous hierarchical structures. SEM images revealed that the as-synthesized In2O3 hierarchical structure was composed of a number of nanorods with average diameter of about 50 nm. It is interesting to note that these In2O3 nanorods were well aligned around a single central symmetric axis, exhibiting an excellent symmetric structure. The response of the gas sensor based on In2O3 hierarchical structure towards 1 ppm NO2 can be as high as 87 at the optimum working temperature and the detection limit can be as low as 40 ppb, which could be attributed to the porous structures and large specific surface area. Besides, Zn O core-shell structure was also studied as a promising sensing material. The Zn O@void@Zn O core-shell structure was synthesized by microwave hydrothermal technology. Meanwhile, a series of time-dependent experiments were carried out in order to have a closer inspection of the formation mechanism of the Zn O core-shell structure. In comparison to the Zn O hollow structure, Zn O core-shell structure has more surface active sites, making it more suitable in gas-sensing applications. The experimental results indicated that the maximum response of Zn O core-shell is about 2 times higher than that of Zn O hollow microspheres.2. The Au nanoparticles were used for modifying the bare Zn O microspheres and their impacts on the performance of oxide semiconductors were well studied. First of all, four different Au-loaded Zn O hollow spheres were prepared by using one-step microwave-assisted method through adding different volume of HAu Cl4 solution respectively. Due to the reaction solution had been under constant stirring, the products were well dispersed with uniform size and the distribution of Au nanoparticles on the Zn O hollow microspheres was very uniform. Using the as-prepared four samples as sensing material, four kinds of gas sensors were constructed respectively. Subsequently, the discrepancy of sensing performances between the unloaded and loaded Zn O samples was investigated. The results showed that the gas-sensing properties of Au-loaded Zn O sample were generally better than the unloaded one, which should be attributed to the "electronic sensitization" and/or "chemical sensitization" of noble metal particles. Among these gas sensors, the response of 1.0 mol% Au-loaded Zn O towards 200 ppm ethanol is twice higher than that of pure Zn O, furthermore, the response and recovery time were also significantly shorter than that of pure Zn O.3. We further synthesized a new-type noble metal@semiconductor composite with core-shell configuration. In a typical process, the Au@Zn O and Au@In2O3 heterostructures were successfully prepared by a facile aging process at room temperature combined with subsequent heat-treatment method using Au@carbon nanospheres as templates. Because of the hierarchical structures of sensing materials and the catalysis of noble metals, the two metal-semiconductor heterostructures showed excellent sensing performance in detecting organic volatile compounds(VOC). The response of gas sensor based on Au@Zn O core-shell structures was as high as 37 towards 100 ppm acetone, which was much higher than that of the other two sensors based on Zn O hollow structures or Zn O solid structures. The maximum response of Au@In2O3 core-shell structure to formaldehyde was more than three times higher than that of In2O3 nanospheres.4. Two other semiconductor heterostructures were prepared by using two kinds of different semiconductors. On the basis of Zn O hollow structure, the Zn O/Zn Fe2O4 double-shell composites were prepared through liquid phase reaction combined with subsequent heat-treatment method for the first time. The results of gas sensing test indicated that the gas sensor based on Zn O/Zn Fe2O4 heterostructure not only exhibited high response towards acetone but also showed fast response and recovery properties. When the sensor based on Zn O/Zn Fe2O4 composites worked at 250 °C, the response and recover time were only 1 and 33 s respectively, which was dozens of seconds faster than that of bare Zn O hollow structure. Such good gas-sensing properties were believed to be related to its unique heterojunction and larger specific surface area.
|
PDF Full Text Request