Electrode Surface Preparation And Application Of Doped Polyaniline

Among conducting polymers, polyaniline(PAN) is a most promising material due to its high conductivity, good redox reversibility, swift change of color with applied potential and good stability in aqueous solutions and air. However, its properties including conductivity, electrochemical activity, electrocatalytic ability, electrochromic phenomenon and the conversion of light to electricity are strongly affected by mediun pH. When pH>5, PAN has a low conductivity and a little electrochemical activity. In this case, PAN almost loses its practical applications. Therefore, pH dependence is a decisive factor that controls the properties and applications of PAN. To improve the properties of PAN, acidic groups (normally sulfo or carboxyl groups) were introduced into the PAN chain and to form a so-called"self-doped"PAN, which can maintain its electrochemical activity in neutral or even basic solutions. In our work, we use amino acid with amino and acidic groups as a dopant for the doping of polyaniline. On one hand, amino acid is immobilized at the carbon electrode by forming the stable C-N covalent bond, on the other hand, this doping PAN films exhibiting electrochemical activity in a wide pH range is presented.This paper includes four sections as followed:1. Electrochemical polymerization of aniline (AN) on orthoanic acid (ABS) functionalized glassy carbon electrode (GCE) and its electrocatalytic oxidation towards ascorbic acid (AA) have been studied. After ABS was covalently grafted on GCE via electro-oxidation procedure, the polymerization of AN was carried out on the ABS functionalized GCE, then PAN-ABS composite membrane modified GCE (PAN-ABS/GCE/CME) was obtained. PAN-ABS/GCE/CME exhibited good electro-catalytic response towards AA oxidation in 0.1 mol/L PBS (pH 6.8) due to the doping of sulfonic acid groups in ABS. The anode peak potential of AA shifted from 0.39 V at GCE to 0.17 V at PAN-ABS/GCE/CME with a greatly enhanced current response. A linear calibration graph was obtained over the AA concentration range of 5.0×10-4～1.65×10-2 mol/L with a correlation coefficient (r) of 0.9973, the detectionlimit (3δ) for AA was 7.2×10-6 mol/L and the linear regression equation is ipa(μA)=20.2+6.20cAA(mmol/L). The modified electrode showed good stability and reproducibility.2. The 3-dimensional (3D) polyaniline (PAN) nanostructures have been synthesized via electrochemical polymerization of aniline using a three-step electrochemical deposition procedure onα-alanine (ALA)-monolayer functionalized glassy carbon electrode (GCE), then PAN nanonetwork/ALA composite film coated GCE (PAN-ALA/GCE/CME) was obtained. The structure and properties of PAN nanostructures have been characterized using field emission scanning electron microscope (SEM), Fourier transform infrared spectra (FT-IR) and electrochemical techniques. The PAN-ALA/GCE/CME leads to the direct electrochemistry of horse heart cytochrome c (Cyt c) immobilized on this electrode surface. The immobilized Cyt c maintains its activity, showing a surface-controlled electrode process with the electron transfer rate constant (ks) of 21.9 s?1 and the charge-transfer coefficient (α) of 0.37, and could be used for the electrocatalytic reduction of hydrogen peroxide (H2O2). The steady-state current response increases linearly with H2O2 concentration from 2.5×10?5 to 3.0×10?4 mol/L. The detection limit (3δ) is 8.2×10?6 mol/L.3. PAN-ABA composite membrane modified GCE (PAN-ABA/GCE/CME) was fabricated by electrochemical oxidation. ABA monolayer of surface-modified glassy carbon electrode was characterized by X-ray photoelectron spectroscopy (XPS) and electrochemical techniques. PAN-ABA composite film had been studied by electrochemical impedance spectrum (EIS) and cyclic voltammetry (CV), demonstrating that the PAN-ABA film has been formed and can maintain its electroactivity in neutral and even in alkaline media. PAN-ABA/GCE/CME exhibited good electro-catalytic response towards AA oxidation in 0.1 mol/L PBS (pH 6.8) and the anode peak potential of AA shifted from 0.41 V at GCE to 0.27 V at PAN-ABA/GCE/CME with a greatly enhanced current response. A linear calibration graph was obtained over the AA concentration range of 5.0×10-5～1.05×10-3 mol/L. The linear regression equation is ipa(μA)=26.82+0.0582cAA(μmol/L), a correlation coefficient (r) is 0.9973 and the detection limit (3δ) is 1.3×10-6 mol/L. Chronoamperometry has also been employed to investigate the diffusion coefficient and the catalytic rate constant of electro-oxidation of AA. The modified electrode showed good stability and reproducibility.4. Orthoanilic acid (ABS) electrochemical covalently modified glassy carbon electrode has been studied in this work, then ABS monolayer film coated GCE (ABS/GCE/CME) was obtained. The structure and properties of orthoanilic acid monolayer film were characterized by cyclic voltammetry (CV) and X-ray photoelectron spectroscopy (XPS) at the same time. ABS/GCE/CME is electrochemical active and stable in cosolvent of ACN and aqueous solution of PBS (pH 6.8). The behaviors of AA and UA on the ABS/GCE/CME were studied by CV and differential pulse voltammetry (DPV). The experiment results indicated that ABS/GCE/CME can resolve the mixed voltammetric response of AA and UA at GCE into two well-defined voltammetric peaks. The separation between the two peak potentials was about 190 mV in CV and 210 mV in DPV, which can be used for the selective determination of these species in a mixture.