The Synthesis And Characterization Of Polypyrrole Modified Films Doped With Humic Acid

Modified electrodes with doped polypyrrole(PPy) are widely researched nowadays. Special function can be obtained by modified electrode with polymer, and the expected reaction can be realized. HA has carboxyls, hydroxyls and other radicals in its molecular structure which can be used in ion exchange, and complexometric with metal ions. Moreover HA is cheap and can be easily got, the application of HA in electrochemistry has a widly perspective. In my work, I try to dope HA in polypyrrole, and PPy/HA modified electrodes can be obtained, furthermore the redox characteristic of it is studied.Cyclic voltammetry(CV) is used to research the electrochemical characteristics of HA, including redox behavior in water without electrolyte and in aqueous solutions of different pH, and stable potential windows of HA is found based on stable electrochemical ranges. It can be concluded that CV of HA in different electrolyte changes greatly with pH. Reduction Oxidation characteristics are evident in acidic solution, in which single or double oxidation peaks can be got by CV, and oxidation peaks change to more negative potential when pH changes lower. However, electroactivity of HA in neutral solution is comparably weak, and shows its better oxidation activity in alkali solution.The result shows that HA can be adhered on Pt electrodes in acidic, neutral and alkali solution. We can see the substance with brown color on the surface of electrode.HA is doped in PPy by potential step and CV. It is found that the eletropolymerization process should be in aqueous solution of pH under 9.0. Range of pH for electropolymerization is between 1.0～9.0 based on the solubility of HA. Electropolymerization process is explained in solution of pH=7.0 and pH=9.0 as examples. PPy film doped with HA is compact and firm.Redox characteristics of electrodes modified with PPy/HA is researched in KOH electrolyte. Redox peaks in electrolyte are evident, and the currents of redox peaks are not linearly proportional to the square roots of scan rates, so the control-step of charge transmit is non-diffusion.Polymer of PPy/HA is analysed by FT-IR. We can conclude there are aromatic ring and its substitute, alkane, alcohols doped in the film just like the carboxyl which oxidated by hydroxy in HA. There are also the characteristic peak of C-N bond with strong peak intensity and sharpe peak intensity which comes from PPy in this film. So we can confirm that HA has been doped in PPy/HA film.