Gas-sensitive Polyaniline / Oxide Composite Film Preparation

There were many disasters in coal mines because of gas exploding recently. Thus, it is very important to monitor gas concentrations quickly and accurately in coal mines. Gas-sensing materials are the core of gas sensors. Comparing with the conventional gas-sensing materials, macromolecular gas-sensing materials expand the application range of gas sensors, due to their low cost, simple preparation, and being used at room temperature, which shows a good solution to solve the problem of high working temperature of usual gas sensor. Nowadays, as the nucleus of gas sensors, the gas-sensing material is changing from simplex materials to composite materials. Organic polymer/inorganic material nanocomposites combine the advantages of polymers and inorganic nano-materials, which endows the nanocomposites with excellent gas-sensing characteristics. The PANI composites are widely used in a lot of fields such as optic field, electronical field, magnetic field, sensitive field and so on, because they not only have small size effect, surface effect and quantum effect of the nano-particles, but also have advantages of macromoclecule. The thesis used the composite material of PANI and inorganic counterparts in nano-size as the gas sensitive material, and contained three sections as follows:First, polyaniline/Indium(III) Oxide(PANI/In₂O₃) nanocomposite thin film was prepared on a quartz substrate by combined techniques of electrostatic self-assembly and in situ chemical oxidation polymerization at 10℃. The film was characterized by scanning electron microcopy (SEM), UV-Vis absorption spectrum and FTIR. Spectrum analyses indicated that some kind of interaction did take place between PANI and In₂O₃ nanoparticles. The morphology analyse revealed that, a typical core-shell structure could be found in the PANI/In₂O₃ nanocomposite material, and It is evident that there are many pores on the surface of the composite thin film. The PANi/In₂O₃ nanocomposite thin film QCM gas sensor was fabricated by using AT-Cut quartz crystal microbalance (QCM) of Ag electrodes, and its sensitive properties to CH₄, CO and NH3 were characterized and analyzed. The results indicated that the PANi/In₂O₃ thin film gas sensor showed good linear sensitive property to CH₄ and CO, while non-linear sensitive property to NH3; the gas sensor was more sensitive to CH₄ than to CO. The sensitive properties of gas sensor in 500ppm CH₄ at different temperature were also tested. The result showed the oscillation frequency value increased when temperature rising. The response value of PANI/In₂O₃ thin film sensor was the biggest value at the room temperature(27℃), and the response value would decrease quickly at very high temperature.Second, PdO was chosen as the other kind of dopant material. PANI/PdO QCM gas sensor was made in the same way of PANi/In₂O₃ QCM gas sensor. Meanwhile, SEM, UV-Vis absorption spectrum and FTIR were used to characterize the composite film. The morphology analyse displayed that PANI/PdO thin film had very small holes. Compared to PANi/In₂O₃ sensor, PANI/PdO sensor had small response value and showed non-linear sensitive property to CH₄. Moreover, when PANI/PdO sensor was explode to CH₄ at high temperature, it showed worse sensitive property than at room temperature.Third, using surface acoustic wave(SAW) device, PANi/In₂O₃ SAW gas sensor and PANI/PdO SAW gas sensor were prepared by the same technique of spin coating. When explode to CH₄ of 0.3%, the result indicated that PANi/In₂O₃ SAW gas sensor showed higher relative response value than PANI/PdO SAW gas sensor.