| In recent years, gas-sensing property of CeO2 has attracted more and more attentions. However, current researches which use pure CeO2 as sensitive material in semiconductor gas sensor are unsatisfactory. CeO2 is stable, abundant and also a good source of the sensitive material. Therefore, it is valuable to seek effective ways to improve gas-sensing performance of CeO2. We chose hydrothermal method as the synthesis method of CeO2, and investigated its I-V curve and sensing behaviour at room temperature using static state method. The main purpose is to improve the gas-sensing properties of CeO2 by reducing the particle size, controlling microstructure and doping modification.The main content is divided into three parts.In the first part, CeO2 nanoparticles were directly synthesized by hydrothermal method, made into CeO2 nano-film by spin coating method, characterized by X-ray diffraction, scanning electron microscope, high resolution transmission electron microscopy and atomic force microscopy. The results showed that the as-synthesized nanoparticles were fluorite phase CeO2 with face-centered cubic in structure, the average grain size was 9.2 nm, and the CeO2 nanoparticles were regularly spherical in shape. It has uniform particle size and single particles are spherical. X-ray photoelectron spectroscopy proved the existence of Ce4+ions. UV-visible spectroscopy diffuse reflectance spectroscopy showed that the optical band gap is 3.18 eV, which belongs to wide band-gap semiconductors. The CeO2 nanoparticles based gas sensor were investigated for its sensing behaviour towards NH3 and H2 S at room temperature. It has been observed that the CeO2 nanoparticles exhibited excellent sensitivity towards NH3 and H2S in ppm range with fast response and recovery process. The sensitivity increased as the gas concentration increased. The sensitivity was higher for NH3 than for H2 S at the same concentration.In the second part, we tried to synthesis CeO2 nanofibers by adding urea as control agent on the basis of alkali boiling method. We found a suitable reaction temperature by analyzing the X-ray diffraction spectra of CeO2 samples synthesised at different reaction temperature. Scanning electron micrographs confirmed that the as-synthesized CeO2 had a nanofiber structure, and the diameter and length of the CeO2 nanofibers weresmaller than that of the CeO2 nanofibers made by traditional alkali boiling method.Moreover, the as-synthesized CeO2 nanofibers showed better gas-sensing performance than CeO2 nanofibers made by traditional alkali boiling method. Then the raw material proportion was optimized through further study, and ultimately the gas-sensing performance of CeO2 nanofibers was greatly enhanced.In the third part, Ag-doped CeO2 were synthesized by hydrothermal method basis on CeO2 nanoparticles and nanofibres synthesized as mentioned in the previous two parts. The spin-coating process was used to prepare the Ag-doped CeO2 thin film. The X-ray diffraction results showed that the two kinds of Ag-doped CeO2 were all face-centered cubic in structure. The X-ray diffraction peaks were corresponding to the standard peaks of CeO2, which meaned that the as-doped Ag didn’t form a single phase.The micrographs showed that the two kinds of Ag-doped CeO2 were uniform in size and spherical in shape. Their grain size were significantly growed bigger than pure CeO2.UV-visible spectroscopy diffuse reflectance spectroscopy showed that the optical band gap of Ag doped CeO2 nanoparticles and Ag-doped CeO2 nanofibers was 3.22 eV and3.20 eV respectively. The spectroscopy spectra is blue shifted after doping Ag in CeO2.The room temperature gas sensing experimental results showed that gas sensing performance of CeO2 nanoparticles have decreased after doped with Ag. It has been observed that the Ag-doped CeO2 nanofibers exhibited excellent sensitivity towards H2 S to a concentration of 2 ppm with a sensitivity of 1.35. |
PDF Full Text Request