Synthesis And Application Of Porous Gas Sensing Metal Oxide Nanomaterials

Improving gas-sensing properties has been being a pursuing goal, in spite of the development of gas sensors based on semiconductor oxides with a long history. Especially for sensitivity and selectivity, they are two important factors, which could affect the application of gas sensors. In order to realize low detection limit and the qualitative identification, the topic about how to improve the sensitivity and selectivity is still a critical issue about the research of gas sensors. Recently nanomaterials and nanotechnology provide new opportunities for improving the performance of gas sensors. In the past several decades, the sensing properties of semiconductor metal oxide nanomaterials have been widely investigated. Owing to the existence of the large activated surface areas, it could cause the detected gas samples to easily diffuse and interact with sensing materials, especially for porous nanomaterials. Therefore, the syntheses of porous nanomaterials would be of importance for improving gas sensing properties.In this dissertation, many porous semiconductor oxide nanomaterials have been prepared. Their sensing and other properties have also been investigated. Furthermore, based on as-prepared hollow and porous In₂O₃ nanospheres, a novel structure sensor device has been fabricated. In order to improve the selectivity of gas sensors, the gas chromatography was employed to separate the mixture sample, combining with gas sensors used to as a detector. The main conclusions are summarized as follows:1. Highly porous (CdO) nanowires have been prepared by calcining the hydroxy and carbonate-containing cadmium compound precursor nanowires in air, which have been synthesized through hydrothermal method. In order to illustrate the formation mechanism of porous structures, the morphology and composition evolvements of precursor nanowires were further investigated under different stages of the calcining process. Gas sensing properties have been explored for the sensor device fabricated with highly porous CdO nanowires. The results demonstrate that it has good response (even for 1 ppm concentration) owing to its special structure, great selectivity to NO_x (no response to reducing organic gases), high signal-to-noise ratio, and low power. Furthermore, the UV-visible absorption spectrum of the porous CdO nanowires presents a broad absorption peak at 505 nm; and the photoluminescence band shifts as excitation wavelength changes. 2. Monodisperse and diameter controllable carbonaceous nanoparticles have been synthesized. Hollow and porous In₂O₃ nanospheres have been prepared by the hydrolysis of InCl₃ using carbonaceous spheres as templates in combination with calcination. Based on the observation of scanning electronic microscopy (SEM) and transmission electron microscopy (TEM), it has been revealed that the as-prepared In₂O₃ nanospheres have a uniform diameter of around 200 nm and hollow structures with thin shells of about 30 nm consisted of numerous 6-13 nm nanocrystal and nanopores. Owing to the hollow and porous structures, In₂O₃ nanospheres possessing more active surface area exhibit a good response, low detection limit and reversibility to some organic gases such as methanol, alcohol, acetone and ethyl ether. In addition, the response mechanism of hollow and porous In₂O₃ nanospheres to organic gases has been proposed. Furthermore, these prepared In₂O₃ spheres showed a UV-visible absorption peak centered at around 309 nm; and their photoluminescence spectra have also been investigated.3. In order to improve the selectivity of gas sensors, the idea of semiconductor sensors combined with the gas chromatography was offered and investigated. Based on as-prepared hollow and porous In₂O₃ nanospheres, a novel structure sensor device has been fabricated, which was used to be a new chromatography detector offering another approach for preparing a portable gas chromatograph. The experimental results show that the above idea is feasible. It could also be helpful for quantitative analysis. Furthermore, the effecting factors, such as the pressure and temperature of column, were also explored.