Characterization of Polyaniline Nanotubes Formed in the Presence of Amino Acids Lijuan Zhang, Hui Peng, Zoran D. Zujovic, Paul A. Kilmartin, Jadranka Travas-Sejdic * Introduction Conducting polymer nanostructures are currently of consi- derable interest both from a fundamental and an applied point of view. In the recent literature, there have been several investigations into applications of conducting polymer nanowires and nanotubes as actuators, [1] drug delivery systems, [2] field emission displays, [3] gas sen- sors, [4] and biosensors. [5] The high surface area of these nanostructures is seen as highly beneficial for these appli- cations. It is also considered paramount to produce well- defined nanostructures for these systems. A number of approaches to the synthesis of conducting polymer nanowires and nanotubes have been presented, such as template synthesis, [6,7] interfacial polymerization, [8] and electrospinning. [9] Recently, it has been demonstrated that polyaniline (PANI) and polypyrrole nanotubes can be made by a template-free process. [10–12] PANI is unique among the conducting polymers due to its low cost, ease of prepa- ration, good control over chemical and physical properties by oxidation and protonation as well as excellent environ- mental stability. [13,14] The electrically conductive form of PANI, in the dark green emeraldine salt form, is usually obtained by chemical polymerization of aniline using an oxidant such as ammonium persulfate (APS) in solutions of strong acids. [15] In this case a bulky granular material is obtained, [16] with a distinctive polaron band at wave- lengths beyond 800 nm. [17] For aniline oxidation in solu- tions buffered above pH 4, a purple-colored solution leading to a non-conducting brown precipitate has been noted with no polaron absorption band. [17] In other reports unbuffered solutions have been used in which the reaction begins at a higher pH value, followed by a drop in pH as protons are liberated from the oxidation of aniline, and the pH falls to values of 2 or less. Under these conditions Full Paper Self-assembled nanotubular structures of polyaniline were chemically synthesized from solutions containing different amino acids with the addition of ammonium persulfate as the oxidant. The materials were characterized by SEM and a range of spectroscopic methods. Spectroscopic characterizations revealed that the synthesized materials had many features typical of chemically synthesized PANI. Some additional features were also found and have been ascribed to non-conducting material formed in the initial stages of the reaction at a higher solution pH. However, UV-vis and 13 C NMR spectra point toward a conductive material as the final product of the reaction. Cyclic voltammetry results also indicate an elec- troactive final product that closely resembles regular PANI in its electrochemical character- istics. L. Zhang, H. Peng, Z. D. Zujovic, P. A. Kilmartin, J. Travas-Sejdic Polymer Electronics Research Centre, Department of Chemistry, University of Auckland, Private Bag 92019, Auckland, New Zealand Fax: (þ64) 9 3737422; E-mail: j.travas-sejdic@auckland.ac.nz 1210 Macromol. Chem. Phys. 2007, 208, 1210–1217 ß 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim DOI: 10.1002/macp.200700013