Reduction of Cr(VI) at a Polyaniline Film:  Influence of Film Thickness and Oxidation State

Abstract

Hexavalent chromium [Cr(VI)] is highly toxic, carcinogenic, and mutagenic to living organisms. In this paper, the reduction of Cr(VI) to the much less toxic trivalent state [Cr(III)] was studied at polyaniline films grown to different thickness. Much higher rates of Cr(VI) reduction were observed for the "thick" polyaniline films. This was explained in terms of the morphology of the polymer and the higher surface area of polymer in contact with the Cr(VI) solution. For "thin" polyaniline films, the Cr(VI) reduction reaction was found to obey pseudo-first-order kinetics for the duration of exposure. However, in the case of thick polyaniline layers, the Cr(VI) reduction reaction followed a twostage process, with each stage obeying pseudo-firstorder kinetics. This was explained in terms of oxidation of the polymer from the leucoemeraldine to the emeraldine state and then further oxidation of the polymer from the emeraldine to the pernigraniline state. Much higher rates of Cr(VI) reduction were observed on oxidation of the polymer from the leucoemeraldine to the emeraldine state.

Magnetite/graphene/polyaniline composite for removal of aqueous hexavalent chromium

“…6 It has good reduction behaviors for Cr (VI) to Cr (III) with the electron transfer from the LB or EB states to PB state. 7 PANI in powder form is a good candidate for highly efficient Cr (VI) removal due to high adsorption capacity, low cost, and easily bulk production. [8][9][10] PANI is macroporous in nature and has small surface area and has been used for adsorption of Cr (VI The most recent discovered synthetic allotrope of carbon, two dimensional graphene and its derivatives have been used in water treatment containing organic, inorganic, and biological pollutants.…”

Electrochemically enhanced reduction of hexavalent chromium in contaminated clay: Kinetics, energy consumption, and application of pulse current

“…A similar method on rate law approximation was previously reported [28], where the Cr(VI) was reduced at polyaniline film surface. Representative kinetic plots under different current densities to fit the first order reaction kinetics are constructed in Fig.…”

“…(1) by its stoichiometric number [28]. The rate law of the overall reaction could be expressed by Eq.…”

Combination of electroreduction with biosorption for enhancement for removal of hexavalent chromium

“…The presence of Cr(III) species had led to the formation of its precipitation after the adjustment of the pH in the above solution using NaOH. White precipitate was observed around pH 7.0, indicating the presence of Cr(III) and the formation of the Cr(OH) 3 precipitate [22].…”