Oxidation of aniline in dopant-free template-free dilute reaction media

► The new nanostructured polyaniline sulfate/hydrogen sulfate is synthesized. ► Novel dopant-free template-free dilute oxidative polymerization method is applied. ► Morphology and molecular structure of polyaniline depends on aniline concentration. ► Oxidative copolymerization of aniline with ortho-aminophenyl sulfate is revealed. ► Oxidative copolymerization of aniline with 4-aminophenol is revealed. The oxidation of aniline with ammonium peroxydisulfate in water without added acid was studied in dilute reaction media. The new nanostructured nonconducting polyaniline sulfate/hydrogen sulfate, synthesized by dilute dopant-free template-free falling-pH method, consists of network of nanorods and nanogranules. The molecular structure of polyaniline, investigated by the elemental analysis, FTIR, Raman, UV–Vis and EPR spectroscopies, was found to be significantly different in comparison with the structure of the nanostructured PANI sulfate/hydrogen sulfate prepared by dopant-free template-free falling-pH method in concentrated aqueous aniline solutions. The mechanism of the formation of nanostructured polyaniline under dopant-free template-free dilute reaction conditions is discussed.