Basic amino acid assisted‐fabrication of rectangular nanotube, circular nanotube, and hollow microsphere of polyaniline: Adjusting and controlling effect of pH value

Abstract

This work reports a simple and effective method to prepare polyaniline (PANI) nanotubes with rectangular or circular cross section and hollow microspheres by using basic amino acids L-lysine or L-arginine as dopants and pH buffer agents, respectively. The research reveals that the pH value of the reaction solution at the beginning stage is a crucial factor to form PANI microstructures. The L-lysine and L-arginine have isoelectric point 9.74 and 10.76, which can maintain reaction solution at high pH value at the beginning reaction and assist aniline to couple in ortho-position forming phenazine unit in the oligomer chain. The oligomer produces rectangular nanorods or microspheres by interaction. These oligomer microstructures act as templates for further polymerization to form PANI rectangular nanotubes and hollow microspheres. Decreasing the concentration of the basic amino acid or using acidic amino acid, the round nanotubes are formed. This method provides a simple route to prepare PANI microstructures with different morphologies without any foreign template or surfactant, and raises a new view on the polymerization process.

Aniline oligomers versus polyaniline

“…In the contrast to the present observations (Fig. 3), microspheres reported in the literature have often been hollow and had an opening 26, 28, 29, 45–47, 50–54. Similar microspheres have also been obtained by freeze drying of polystyrene latex particles swollen with toluene 55, 56.…”

“…7(c)). Quinoneimine units have indeed been identified in recent NMR experiments27–30 (Fig. 7(c), (d)) and are responsible for the presence of oxygen in the samples.…”

“…The crosslinking of polymer chains to produce phenazine‐like units seems to be preferred over simple degradation. The fact that nitrogen atoms are included in the products is of importance when the resulting materials are used as catalyst supports24, 115 or in supercapacitors112, 116 and electrorheological fluids 28, 29, 113, 114. The morphology of PANI is preserved during the carbonization;66, 110 this allows for the preparation of various carbonaceous nanostructures.…”

“…Oxidations of aniline started under alkaline conditions, pH > 7, have often been referred to as alkali‐guided syntheses of PANI20–24 but in fact PANI in the emeraldine form is not produced 5, 25. The formation of microspheres was reported during the oxidation of aniline in alkaline5, 20, 25 and also in mildly acidic media 26–29. Venancio et al 26 proposed that the oxidation products associated with microspheres represent a new class of PANI, polyazane, containing NN‐linked constitutional units.…”

Electrosynthesis of poly(3‐amino‐4‐hydroxybenzoic acid) nanoparticles with electroactivity even in highly alkaline solutions

“…Several methods, which include electrospinning, chemical polymerization, and electrochemical polymerization, have been used for preparing the nanostructures of polyaniline . The conventional chemical polymerization can be used to make bulk quantities of nanostructured polyaniline with the aid of insoluble templates, soluble templates, or biological templates.…”