Factors affecting the radical scavenging activity of polyaniline

Polyaniline was chemically synthesized by oxidizing aniline with ammonium persulfate with and without hydrochloric acid (G-PANI and NR-PANI, respectively). NR-PANI and G-PANI were dedoped with ammonium hydroxide to yield NR-PANIdd and G-PANIdd. SEM images revealed a typical granular morphology for G-PANI and G-PANIdd, while NR-PANI, formed using a ‘falling pH method’, and NR-PANIdd, consisted of micro/nanorods and flakes. The samples were characterized using FTIR and the level of oxidation was determined by X-ray photoelectron spectroscopy (XPS). The surface area of the samples was measured by the BET method. The free radical scavenging activity, using the DPPH assay, showed the following ranking: NR-PANI > G-PANI ≈ NR-PANIdd > G-PANIdd. The radical scavenging activity of the polyanilines did not correlate with conductivity or surface area measurements, but was critically dependent upon the level of oxidation, and higher activity was obtained with the more reduced polyaniline samples.

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► Polyaniline nanorods formed under falling pH conditions are superior radical scavengers to granular polyaniline.
► Polymer oxidation state determines radical scavenging capacity ahead of surface area or conductivity.
► Granular polyaniline has a higher BET surface area than polyaniline nanorods.