Polyaniline–Poly(vinyl alcohol) Dispersions for Controlled Ion Exchange of Organic Sulfonates

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Abstract
The authors prepared colloidal dispersions consisting of polyaniline, dopant (perchlorate, benzenesulfonate or polystyrene sulfonate) and surfactant stabiliser [poly(vinyl alcohol)]. The dispersions took up anionic analytes in their oxidised forms and ejected the anions on deprotonation or reduction. Thus, uptake and release were controlled externally by varying the redox potential and/or pH in solution. Organic anions such as chromotropic acid anion and anthraquinone sulfonates were taken up quantitatively into the oxidised dispersion particles and concentrated 250–1000 times. Although the uptake of these anions was quantitative, ejection from the deprotonated or reduced forms was not so. In order to achieve high ejection efficiency, we prepared a dispersion of doping polystyrene sulfonate to introduce immobile negative charge. As a result, the recovery of chromotropic acid increased up to 100% at the cost of uptake capacity. Competitive interactions of the negative charge and targeted anion with the cationic sites in polyaniline were confirmed by electrochemical and electron spin resonance measurements and were responsible for the increase in the recovery. Electrochemical ejection of chromotropic acid was found to be quantitative when methyl viologen was present in solution as an electron mediator.

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