Polypyrrole nanotubes versus nanofibers: A proposed mechanism for predicting the final morphology

• A mechanistic discussion is proposed to justify the formation of tubular and fibrillar morphology.
• The ratio of the reaction components was found to be responsible for the final morphology.
• The monomer addition method can affect the morphology of PPy.

This work addresses the preparation of polypyrrole (PPy) nanostructures using a template based on methyl orange (MO) and iron(III) chloride (FeCl3). A mechanistic discussion is proposed to justify the effect of reactants molar ratios (Py:MO:FeCl3) on the final polymer morphology. Fourier transform infrared (FT-IR) spectroscopy, CHNS elemental analysis, and Ultraviolet–visible (UV–vis) spectroscopy were applied to prove the proposed hypothesis. The results indicated that utilization of relatively high amount of monomer possibly ensures the occurrence of template degradation process resulting in the formation of a hollow tubular structure; while the presence of low amount of pyrrole leads to a non-hollow fibrillar morphology. The relative molar ratio of MO:FeCl3 is supposed to be important for formation of template-based nanostructures. The effect of monomer addition method on the morphology of the final polypyrrole was also investigated, indicating that dropwise addition of pyrrole leads to the formation of PPy well-formed nanotubes, while the instantaneous addition manner results in formation of nanoparticles, as well.