Adsorption and Reduction of Cr(VI) Together with Cr(III) Sequestration by Polyaniline Confined in Pores of Polystyrene Beads

Abstract

The simultaneous reduction and sequestration of Cr(VI) from wastewater is desirable as a cost-effective and environmentally friendly approach. In this study, we execute a one-step facile synthesis strategy on polyaniline (PANI) composites based on aniline adsorption and polymerization on pores of millimeter-scale polystyrene balls (PANI@PS). The well-defined PANI@PS increased the removal capacity of Cr(VI) by 5.4 times, going from 43.6 (bulky PANI) to 233.7 mg g −1 near neutral pH (6.0) instead of the pH 1−3 documented in other reports, which was higher than that of many reported adsorbents due to its porous structure, numerous interaction sites, and confinement effects in the polymer. Most importantly, PANI@PS could efficiently sequester positive Cr(III) after reducing Cr(VI) to Cr(III) due to its negative surface created by confinement effects confined to the nanopores of PS. Conversely, positively charged bulky PANI repelled electrostatically positive Cr(III); thus, additional precipitation or adsorption treatments were needed in practical applications. Moreover, a coating of PANI can protect PS, as a substrate and a composite, from irreversible damage due to the strong oxidation capacity of Cr(VI), which is another major concern in adsorbing strong oxidants using polymers. A novel strategy to regenerate the exhausted PANI@PS was efficiently executed based on the electrochemical redox reversibility of PANI. Finally, the comprehensive adsorption/reduction/sequestration of Cr on PANI@PS was elucidated in detail.

Direct Z-scheme α-MnO2@MnIn2S4 hierarchical photocatalysts with atomically defined junctions for improved photocatalytic activities

“…Moreover, dealing with highly toxic hexavalent chromium is a difficult task in the treatment of world environmental pollution 13,14 . Based on trivalent chromium's low toxicity and easy flocculation into Cr(OH) 3 in an alkaline environment, reducing Cr (VI) to trivalent chromium has become a key procedure for environmental remediation 15,16 . Among the currently developed reduction methods, the photocatalytic reduction has shown potential application prospects compared with the high-cost chemical reduction method 17 and the biological reduction method 18 with high environmental requirements.…”

Effective Adsorption of Hexavalent Chromium and Divalent Nickel Ions from Water through Polyaniline, Iron Oxide, and Their Composites

“…Accumulation of Cr(VI) in living tissues even in a very small concentration may cause severe neurological or physiological damage. The maximum permissible concentration of Cr(VI) in water is about 0.05 mg•L −1 as accepted by the World Health Organization (WHO) [8]. Perforation of the eardrums and the nasal septum, skin Adsorption data were fitted in the Freundlich, Langmuir, Dubinin-Radishkevitch (D-R), Tempkin, and Elovich isotherm models.…”

Preparation of Hollow Polyaniline Micro/Nanospheres and Their Removal Capacity of Cr (VI) from Wastewater

“…For example, the used hollow PANI micro/nanoshpheres are further treated with 1 M HCl for 0.5 h and then reused for Cr (VI) removal. It can be found from Table 2 that the removal capacity of the first reused hollow PANI micro/nanoshpheres is probably close to the initial PANI removal capacity [26, 37]. It can be concluded that the hollow PANI micro/nanospheres are a reproducible material for Cr (VI) removal.

Scheme 1Schematic illustration the conversion between pernigraniline and emeraldine of PANI

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