The Morphology And Electrochemical Properties Research Of Doped Poly(N-methylpyrrole)

Poly(N-methylpyrrole) is the derivative of non-carcinogenic conducting polypyrrole. In recentyear, poly(N-methylpyrrole) has attracted numerous scholars and became a hot researchs due to highconductivity, good stability, ease synthesis, mechanical flexibility etc. In practical applications, theeigenstates poly(N-methylpyrrole) has some limitations. By doping，however, the morphology andelectrical properties of poly(N-methylpyrrole) have been changed largely. Thus, finding suitable dopant isespecially important for improving conductivity of poly(N-methylpyrrole). In this paper,poly(N-methylpyrrole) was polymerized on graphite electrode by electrochemical technique. Thepolymerization conditions of N-methyl pyrrole were optimized for hydrochloric acid as supportingelectrolyte. Based on above works, several sulfonates and dyes were doped into poly(N-methylpyrrole).The results show that the electrochemical polymerization method can make up the disadvantage of thechemical oxidation which can not form an adhesion film on the electrode surface. In addition, themorphology of films of Poly(N-methylpyrrole) with different characteristics can be obtained and theconductivity of the film was improved by doping. The details are as follows.First, the poly(N-methylpyrrole) film dopped Cl-was deposited on the surface of pencil electrodeusing potentiostatic method in traditional three-electrode system. The polymerizen conditions ofN-methylpyrrole (such as pH, potential, time and temperation of polymerization) were optimized and theinfluence of the conditions on the morphology and electrochemical properties of poly(N-methylpyrrole)was discussed. The results showed that the poly(N-methylpyrrole) film obtained has relatively smoothsurface, good adhesion on pencil electrode and easy exchange of Cl-under the optimized conditions (25℃,0.7V, pH=1and70min) Secondly, the poly(N-methylpyrrole) film doped sulfonate were investigated. The dopedpoly(N-methylpyrrole) film was prepared by changing the molar ratio of N-methylpyrrole and sulfonate.The morphology and electrochemical properties of the doped film were analysed by SEM, CV and EIS.SEM results show that the surfaces of poly(N-methylpyrrole) film undoped with sodium benzenesulfonate/Sodium p-toluenesulfonate have a number of horn-like bump and the film surfaces doped with3-Nitrobenzenesulfonic acid sodium salt/3-Carboxybenzenesulfonic acid sodium salt are mainly typicalnodular,‘cauliflower’ appearance. CV and EIS shows that for the sulfonate-doped Poly(N-methylpyrrole),the film conductivity originates in insertion and extration of smaller ions (Cl-) in solution instead of thesebenzene sulfonic acid radical ions in the film due to the larger steric hindrance of benzene sulfonic group.Finally, the poly(N-methylpyrrole) film doped with different dyes were prepared andcharacterized by the same methods mentioned above. The results show that the surfaces of film doped withrhodamine B/methylene blue are mainly ‘cauliflower’ appearance and the surface of film doped withmalachite green is composed of microspherical grains. Furthermore, the poly(N-methylpyrrole) films dopeddye has better stability of electrochemistry.