Preparation And Sensitive Properties Of ZnO And Conductive Polymer Nanocomposite Gas Sensitive Materials

Gas sensors have been widely used in many fields such as agriculture,military,environmental monitoring and so on.With the rapid development of the information society,it is urgently needed to greatly improve the sensory characteristics of the sensors,which can be effectively realized by preparing nanostructured sensing materials and their composites.In this paper,a method which combines electrospinning and hydrothermal synthesis has been proposed for in-situ growth of nanostructured ZnO on the substrates.Specifically,ZnO with different morphology(ZnO nanoparticles and nanosheets)could be obtained by modifying the hydrothermal conditions,and the reaction was completed in the aqueous solution in the absence of organic solvents or additives.Therefore,it circumvents the calcinations of nanofibers and the redispersion of nanomaterials,and represents a simple and green process.Composites of nanostructured ZnO and polypyrrole(PPy)were prepared by vapor phase polymerization of pyrrole on the surface of ZnO.The morphology,composition and structure of the composites were characterized by FESEM,XRD,FT-IR and HRTEM.NH3 sensing properties of nanocomposites were examined at room temperature,and the effect of the morphology of ZnO on the response of the composite was also investigated.The results showed that the composites of ZnO nanosheets and PPy exhibited the optimal sensing properties,whose relative change of resistance to 10 ppm NH3 was 76%,nearly 30 times higher than that of PPy.Moreover,the composites revealed excellent selectivity and good repeatability.It is proposed that good contact between the sensing materials and the substrate,high specific surface area of the nanocomposites and p-n junction formed at the interface between PPy and nanostructured ZnO all contribute to the enhancement in the sensitivity of composites,with the formation of p-n junction playing a key role.The dispersible conducting PANI with different morphologies were prepared by the method of post doping,rapid mixing and template polymerization.Nanocomposites of ZnO with PANI were fabricated by dip coating dispersible PANI on ZnO or via the in-situ solution or vapor phase polymerization of aniline on the surface of ZnO.The effects of the nanostructure of ZnO,the morphology,structure and preparation methods of PANI on sensing properties of the composites were studied.The composites of vapor phase polymerized aniline and ZnO nsnosheets revealed the highest sensitivity,whose relative change of resistance towards 10 ppm NH3 was up to 2150%,about 10 times higher than that of PANI alone.Meanwhile,the composites exhibited an extremely low detection limit(5 ppb),excellent selectivity and good repeatability.It is suggested that the p-n junction formed at the interface of nanostructured ZnO and PANI significantly improved the sensitivity of the nanocomposites.