Preparation Of Poly(Ionic Liquids) And Graphene Composites And Their Gas Sensing Properties

With the growing attention on gas monitoring for environmental protection,safety,and health,there is a strong demand and research significance for developing novel gas sensing materials with high-performance and efficiency.Poly(ionic liquids)(PILs),which possess various designable molecular structures and abundant active sites,have been treated as one of the important candidates for sensing materials.On the other hand,due to the unique physicochemical properties,graphenes have also attracted great attentions for gas sensing.We suggest that the combination of PILs and graphene may improve the disadvantages of graphene such as easy stacking and lack of active sites for sensing performance and may futher promote the application of graphene composites for gas sensing.Based on the above viewpoints,we carried out the work of this thesis from the following content:1?Preparation of imidazole-type PILs.Using different polymerization methods,PILs were prepared with imidazole group located in the branch or main polymer chain.PILs with different anions were also prepared by anion exchanging.The structure,thermal stability and solubility of PILs were studied and compared.The results show that PILs are very stable within 200 °C,and the addition of benzene in the branch of the polymer chain can improve the thermal stability.The PILs can be soluble partially in polar solvents and their solubility can be altered by changing the anionic structure.2?Preparation of PILs/rGO composites.PILs/rGO composites were prepared by reducing the mixture of graphene oxide(GO)and PILs using high pressure steam.The structure of PILs/rGO composites with varied composite ratios were studied.The results show that PILs can be well combined with rGO.The addition of PILs may increase the disorder of rGO and promote the formation of N-doped rGO.3?Gas-sensing properties of PILs.PILs were deposited on the electrod of quartz crystal microbalance(QCM)for gas sensing by drop-coating or spray-coating.Sensitive properties of PILs to common organic gases were tested.The QCM sensing electrodes have good comprehensive adsorption performance when the coating mass of PILs is around 200-250 ng.Electrodes prepared by spray coating can achieve better sensing effect.PILs show good sensitivity and selectivity for carboxylic acids.The QCM sensing electrode coated with 223 ng of branched PILs show a theoretical limit of detection of 1.32 ppm and recovery time within 40 s.The sensitivity and selectivity of PILs can be modulated by altering anions.We also estimate the sensitive mechanism of PILs according to fourier transform infrared spectroscopy(FTIR).4?Gas-sensing properties of PILs/rGO composites.The gas-sensing properties of the PILs/rGO composites were tested using interdigitated electrode.The response of the composites to ethanol,acetic acid and ammonia show more than three times higher than that of rGO,while the response to acetone and benzene are less improved.The composites exhibit high sensitivity to acetic acid and ammonia with different concentrations,in which the composite with the branched PILs involving benzene has the best performance.The sensing mechanism of composites was discussed based on the properties of semiconductors and polymers.