Hexavalent chromium removal mechanism using conducting polymers.

We report detoxification of Cr(VI) into Cr(III) using electrochemically synthesized polyaniline (PANI), polypyrrole (PPY), PANI nanowires (PANI-NW) and palladium-decorated PANI (PANI-Pd) thin films. Percent Cr(VI) reduction was found to be decreased with an increase in pH from 1.8 to 6.8 and with initial Cr(VI) concentration ranging from 2.5 to 10mg/L. Efficacy of PANI increased at higher temp of 37 °C as compared to 30 °C. PANI-Pd was found to be most effective for all three initial Cr(VI) concentrations at pH 1.8. However, efficacy of PANI-Pd was significantly reduced at higher pHs of 5 and 6.8. Efficacy of PANI and PANI-NW was found to nearly the same. However, there was a significant reduction in effectiveness of PANI-NW at 10mg/L of Cr(VI) at all the three pHs studied, which could be attributed to degradation of PANI-NW by higher initial Cr(VI) concentration. PPY and PANI-NW were found to be highly sensitive with respect to pH and Cr(VI) initial concentration. Chromium speciation on PANI film was carried out by total chromium analysis and XPS, which revealed Cr(III) formation and its subsequent adsorption on the polymer. PANI-Pd and PANI are recommended for future sensor applications for chromium detection at low pH.