Research Of Gasochromic PAN Nanofiber Membranes

Nowadays,based on the advantages of high specific surface area,high porosity,small weight and easy to be functioned,nanofibers have been widely used in the construction of gas sensors.The research about colorimetric or fluorescent detection of nerve agents by electrospun nanofibers is important,but less in the domestic.In this paper,we combined the Congo red or Methyl red with polyacrylonitrile?PAN?solution,aimed to prepare a new protective material called gasochromic PAN nanofiber membranes by electrospinning.The membranes used to detection of HCl gas.We also investigated the performance of membranes.We tested the properties of solution,studied the spinning-ability of the solution and analysed the influence of the dyes.Then we observed the morphological changes of the nanofibers by SEM and analysed the size and distribution of the nanofiber diameter.It was found that the conductivity of PAN solution increased with the mass concentration of Congo red increased.Methyl red could not influence the conductivity of PAN solution.Also the viscosity and surface tension of PAN solution were hardly affected by dyes,too.PAN nanofibers can maintain the original good morphology.It meant the process of dyeing is smooth.With the mass concentration of Congo red increased,the average size of fiber diameter became smaller and the diameter dispersion became larger.The average size of fiber diameter was not affected by the mass concentration of Methyl red.Used by colorimetric detection,the study investigated the color change of the nanofiber membranes before and after the exposure of HCl gas.It was found that when PAN nanofiber was exposed to HCl gas,the color of membrane turned from pink to blue-purple.The color difference of Methyl Red-PAN nanofiber membrane was not as obvious as that of Congo red-PAN nanofiber membrane.With the volume concentration of HCl gas and Congo red increased,the time for color change is shorter and the color of Congo red-PAN nanofiber membrane gradually shifted to blue until the reaction was completed.Also the color would not be changed any more.The nanofiber membrane is the reaction site.H₂ O and HCl,which was adsorbed on the surface of the nanofiber membrane,generated H₃O⁺.That the Proton exchanged made the conjugate structure changed and the color of membranes changed.When PAN nanofiber was exposed to HCl gas?29.40?L/L,50 m L?,the phenomenon of color change was the most obvious within 10 s.The lowest detection limit is 0.37?L/L of 1L HCl gas.And Congo red-PAN nanofiber membrane has good selectivity to acid gas.Finally,the performance of PAN nanofiber membrane was studied,including pore size,air permeability,filtration and mechanical properties.The results showed that when the mass concentration of Congo red is constant,with the increase of spinning time,the average pore size decreased,the air permeability decreased,the filtration efficiency became higher,the filtration resistance became larger,the breaking strength and elongation increased.However,these properties were not directly related to the mass concentration of Congo red.It indicated that the mass concentration of Congo red was not the main factor of these properties.