Investigation Of Gas Sensor Based On Nano Zinc Oxide-polyaniline Hybrid Film

In the past several decades,metal oxide materials such as ZnO have been intensively studied in the field of gas sensor.These gas-sensing materials with excellent sensing performance are cheap and can be compatible with microelectronic circuits.However,sensors based on metal oxide semiconductor materials often require extra heating devices,which is not suitable for flammable gas detection.This disadvantage along with poor selectivity greatly limit its wide use.Polymer materials such as PANI are widely applied for gas detection at room temperature.Doping,modification and other methods are used in the preparation process of PANI to flexibly adjust gas-sensing properties of the polymer,especially,to achieve a preferred selectivity towards a specific target gas.The main idea of this paper is to synthesize nanocomposites by combining nanoscale metal oxide material with polymer material.The synergistic effect between the two materials can overcome the inherent defects,lower operation temperature.Besides,nanocomposites sensing films are able to optimize gas-sensing characteristics as well as improve selectivity towards a particular gas.UV irradiation was also adopted to improve room temperature sensing performance of the metal oxide semiconductor and hybrid films.The surface morphology and structure features of the sensing films were characterized by means of SEM,XRD,UV-vis and FT-IR to provide strong support for performance improvement.?1?Firstly,ZnO nanorod arrays were prepared by simple one-step hydrothermal method.The PANI dispersion was deposited on the surface of ZnO thin films by spray coating method to prepare ZnO-PANI hybrid film.Sensing characteristics of hybrid film to NH₃ with the concentration of 10-50 ppm were investigated at room temperature.For the purpose of comparison,single-layer ZnO thin film and PANI thin film were prepared.Response of hybrid film to a variety of interfering gases were measured.The results show that hexagonal wurtzite ZnO nanorods are vertically grown on the surface of the substrate.The nanorods are in good contact with each other and there are some nanoscale gaps among them.FT-IR spectra indicate that there is a certain interaction between PANI and ZnO nanorods.Upon exposure to NH₃,ZnO-PANI film and PANI film show considerable increase in resistance,wheares the ZnO film shows no response.It's obvious that ZnO-PANI film exhibits a much higher response than that of PANI film.The higher response can be attributed to the larger surface area of ZnO nanorods,which can provide sufficient adsorption sites,and the formation of p-n junctions between organic and inorganic materials,which can lower the activation energy of gas adsorption.With the increase of hydrothermal time,length of naonrods increases significantly and the surface of the nanorods arrays become more rough,which leads to the slight improvement of the sensitivity of the hybrid film to NH₃.The sensitivity increases by 10% for every 1.5 hours of hydrothermal time.?2?ZnO thin films were prepared using ZnO nanoparticles as sensitive materials,and the NO₂ sensing performance of the films was investigated under UV irradiation.PANI films and ZnO-PANI hybrid films with various structures and different parameters were prepared.The influence of the preparation conditions on the device performance were well carefully studied.Optimum structure and parameters were determined.Then,gas response of device based on hybrid film with optimum parameters was tested towards a variety of interfering gases.Finally,the sensing mechanism of UV-enhanced NO₂ sensor was proposed.The results show that the UV irradiation can increase the carrier concentration in the ZnO material and improve the surface activity of the sensing material to obtain a good room temperature NO₂ gas sensing response.For the pure ZnO thin films,the nanoparticles are agglomerated and can't efficiently absorb the UV light,which will lead to a slight decrease in response with the increase of deposition amount.ZnO-PANI hybrid films taking advantages of ZnO and PANI materials achieve a good gas-sensing response and reduces the phenomenon of baseline drift.At last,we find that that PANI-ZnO bi-layer film with proper resistance are most sensitive to NO₂ at room temperature under UV irridation.