Unusual neutral pH assisted electrochemical polymerization of aniline on a MWCNT modified electrode and its enhanced electro-analytical features

Abstract

Unusual electropolymerization of aniline to polyaniline (PANI) in a neutral pH solution has been successfully demonstrated using a multiwalled carbon nanotube (MWCNT) modified gold electrode (Au–MWCNT@PANI_pH7). The modified electrode showed highly redox active surface confined peaks corresponding to the molecular transitions of leucoemeraldine–emeraldine and emeraldine–pernigraniline in pH 7 phosphate buffered solution (PBS), along with a low capacitance behavior, in contrast to the conventional acidic solution PANI systems. Control experiments in the absence of MWCNTs (i.e., Au/PANI_pH7) and in an acidic medium, pH 2 (i.e., Au–MWCNT@PANI_pH2), resulted in nil and poor redox features respectively. The physicochemical characterization of the MWCNT@PANI_pH7 film by TEM, Raman spectroscopy, FTIR and UV-Vis revealed the presence of polaron type PANI structures on the MWCNT surface. More interestingly, MWCNT@PANI_pH7 showed a highly selective electrocatalytic signal to ascorbic acid (AA) at a low oxidation potential, −15 mV vs. Ag/AgCl, without interference from nitrite, uric acid, dopamine, glucose, cysteine and citric acid in pH 7 PBS. Extended flow injection analysis yielded an excellent AA sensing response with a detection limit (signal-to-noise ratio = 3) of 42 nM, which is better than that of the conventional acid assisted MWCNT@PANI_pH2 and MWCNT systems.