Cr(VI) reduction coupled with Cr(III) adsorption/ precipitation for Cr(VI) removal at near neutral pHs by polyaniline nanowires-coated polypropylene filters

Abstract Background Limited work was done about remediation of Cr(VI))-contaminated water at near neutral pHs (6-8), such as drinking water resources. Methods Polyaniline nanowires-coated polypropylene filter (PANI-PP filter) was fabricated for easy recollection and reuse of spent adsorbents. The physicochemical properties of PANI nanowires were characterized by SEM, FTIR, BET, and XPS. The effect of solution pH, contact time, and Cr(VI) concentration on Cr(VI) reduction and total Cr removal are investigated with batch and column adsorption experiments. Findings The PP filter provided micro-sized fiber for PANI deposition, and the deposited PANI nanowires exhibited higher surface area and Cr(VI) removal ability than the PANI powders formed in synthetic solution. At near neutral pHs, Cr(VI) removal by PANI-PP filter was attributed to the Cr(VI) adsorption by the amine groups, Cr(VI) reduction to Cr(III), and subsequent Cr(III) adsorption/precipitation on the PANI nanowires, and the maximum removal capacity of Cr(VI) and total Cr were in the range of 55.7 to 113.8 mg/g PANI. The Cr(VI) reduction was accompanied with the oxidation of amine groups to imine groups of PANI. The electro-chemical regeneration promoted the reduction of imine groups back to amine groups, and after 10 regeneration cycles, around 105% Cr(VI) removal efficiency was still achieved.