Structural characteristics of polyaniline nanotubes synthesized from different buffer solutions

Polyaniline (PANI) nanotubes were chemically synthesized from different aqueous buffer solutions: citric acid/phosphate (pH 3 and pH 4 as prepared) and HCl/phthalate (pH 3), beginning with 0.2 M aniline (its presence raises the pH) in the presence of the amino acid alanine and using ammonium persulfate (APS) as the oxidizing agent. For comparison purposes, reactions were also carried out in the absence of any pH controlling agents and from HCl/KCl solution (pH 2). To reveal the effects of the buffer conditions on the morphology and structure of the aniline oxidation products, samples were collected at different times and at different pH values during the polymerization when the pH declines due to acid release from aniline oxidation. The products obtained from the buffer solutions were characterized by SEM, FT-IR, and EPR spectroscopy and compared to the products obtained using "standard" conditions, i.e., without pH buffering. Nanotubes were detected in all of the buffered solutions after 20 h. However, the growth rate and the characteristics of the materials at an early stage of the polymerization process (0 to 5 h) were different for various buffers. In general, the appearance of 860 and 1416 cm^-1 peaks in FT-IR spectra of the products indicated the presence of nonconducting products generated at the early stages of the reaction and related to roselike morphology. The exception was the aniline oxidation products from citric acid buffer pH 3, which showed a bent tapelike morphology, and its FT-IR spectrum did not show 860 and 1416 cm^-1 peaks.