The Efficiency of Toxic Chromate Reduction by a Conducting Polymer (Polypyrrole): Influence of Electropolymerization Conditions

Studies of pollution due to hexavalent chromium are important because it represents a risk to human health and the environment. Hexavalent chromium is a toxic substance and has been found to be carcinogenic. Fortunately, its reduced form, Cr(III), is much less toxic. This paper discusses the remediation Cr(VI) by its reduction in aqueous media by polypyrrole (PPy)-coated reticulated vitreous carbon substrates (RVC). The study is focused on the effect of PPy-film electropolymerization conditions and its efficiency toward the reduction of toxic chromate. We have studied parameters such as the influence of the polymerization electrolyte, the scan rate, the potential limits, and the polymerization cycles concerning the reduction capability of the film. Key results obtained in the present study show that in the presence of different anions during formation of the PPy film, the efficiency of chromate reduction depends on the nature of the anion. We found that the films prepared and treated in the presence of KI performed much better and lasted much longer than those prepared in the presence of KF. Films synthesized at lower scan rates, and higher positive potential limits showed higher chromate reduction efficiencies. Some of our results show reduction of ca. 100% of Cr(VI) from a 10 mg/L solution, even after using the film in 20 contacts with the chromium solution, with films synthesized in KBr and KI electrolytes, at a scan rate of 20 mV/s, between −0.3 and 0.9 V and 40 polymerization cycles. Our study shows that remediation of Cr(VI) by reduction with PPy-coated substrates could be developed into an effective method toward the solution of this problem.