Redox Reactions without Direct Contact of the Reactants. Electron and Ion Coupled Transport through Polyaniline Membrane

Solid-state reduction of silver nitrate with polyaniline base leading to conducting materials

The polyaniline (PANI) base was ball-milled with silver nitrate in the solid state. Samples were prepared at various mole ratios of silver nitrate to PANI constitutional units ranging from 0 to 1.5 for three processing times, 0, 5, and 10 min. The emeraldine form of PANI was oxidized to pernigraniline, and the silver nitrate was reduced to metallic silver. Nitric acid is a byproduct, which may protonate the residual emeraldine and pernigraniline. The changes occurring in the structure of PANI are discussed on the basis of Fourier transform IR and Raman spectroscopies. Raman spectra revealed the formation of pernigraniline salt. The reaction between the two nonconducting components, emeraldine base and silver nitrate, produced a mixture of two conducting components, emeraldine or pernigraniline nitrate and metallic silver. The accompanying conductivity changes were determined. The increase in the conductivity of the original base, 10(-9) S cm(-1), up to 10(-2) S cm(-1) was found to depend on the mole ratio of silver nitrate to PANI base and on the processing time of the components in the ball mill.

Bienzyme system for the biocatalyzed deposition of polyaniline templated by multiwalled carbon nanotubes: a biosensor design

A novel method based on covalent attachment of two enzymes, glucose oxidase (GOD) and horseradish peroxide (HRP), onto carboxylic-derived multiwalled carbon nanotubes (MWNTs) for the deposition of electroactive polyaniline (PANI) under ambient conditions is described. Ultraviolet-visible spectroscopy, Fourier-transform infrared (FTIR) spectroscopy, and transmission electron microscopy were used to characterize the assembling of bienzyme and the morphology of PANI|MWNTs. Under the bienzyme biocatalytic condition, a head-to-tail structure of PANI templated by MWNTs was formed. The voltammetric characteristics of the resulting biosensor were investigated by cyclic voltammetry in the presence of glucose. The current response of PANI was linearly related to glucose concentration between 0.05 and 12.0mM with a correlation coefficient of 0.994. The synergistic performance of bienzyme, highly efficient polymerization, and templated deposition provide a general platform for the synthesis of nanowires and nanocircuits, the construction of bioelectronic devices, and the design of novel biosensors.

Polymerization of Aniline on Polyaniline Membranes

When solutions of aniline hydrochloride and ammonium peroxydisulfate were separated by a semipermeable cellulose membrane, the reactants met at the membrane and produced a polyaniline (PANI) membrane at the interface. The oxidative polymerization of aniline then proceeded in situ on the PANI-cellulose composite membrane. PANI was produced entirely at the monomer side of the membrane; about 80% conversion of aniline to PANI was observed after 24 h. The oxidation of aniline with peroxydisulfate consists in the transfer of electrons from aniline to the oxidant; it is proposed that electrons pass through the PANI membrane, which is conducting, and electroneutrality is maintained by the simultaneous transfer of protons. The reaction between aniline and peroxydisulfate thus takes place without the need for both reactant molecules to be in physical contact. The residual aniline is located only at its original side of the membrane, but the product of ammonium peroxydisulfate conversion, ammonium hydrogen sulfate, was found on both sides of the membrane. Fourier-transform infrared spectroscopy has been used to analyze PANI, the reaction residues and byproducts, and to prove that PANI is protonated with counter-ions of the sulfate type. Using this technique, we have detected only small differences in the molecular structure of PANI prepared with the membrane-separated reactants and in the polymerization when reactants were mixed; also, the molecular weights differed only marginally. The conductivity of both types of PANI was about the same. The repeated polymerization of aniline on the earlier prepared PANI-cellulose membrane yielded similar results, thus confirming the proposed concept of coupled electron- and proton-transfer through the PANI membrane.