Reduction of Hexavalent Chromium in Aqueous Solutions by Polypyrrole

Spontaneous electron transfer, along with anion uptake by doping, form the basis of a new concept for the reduction of toxic Cr(VI) using an electronically conductive polymer, e.g. , polypyrrole. Proof of concept experiments are described which show that aqueous sulfuric acid solutions containing 5–100 ppm Cr(VI) can be thus converted at ∼100% efficiency to the environmentally more tractable Cr(III) species at time intervals spanning several minutes. The reversibility of the polymer redox process enables the electrochemical recycling of polypyrrole for repeated treatment of Cr(VI). The key advantages relative to the chemical and electrochemical cleanup strategies currently employed include those related to material recyclability, selectivity, and efficiency at low (ppm) Cr(VI) levels.