Chromate removal by electrospun PVA/PEI nanofibers: Adsorption, reduction, and effects of co-existing ions

Abstract

Chromium (Cr(VI)) is one of the most toxic heavy metals threatening humans’ health and the environment. Water-stable poly(vinyl alcohol)/polyethylenimine (PVA/PEI) nanofibers were fabricated through electrospinning and evaluated for Cr(VI) removal from water in batch experiments. The adsorption behavior and removal mechanisms of Cr(VI) by PVA/PEI nanofibers were systematically investigated through a combination of batch experiments and spectroscopic characterizations. The Cr(VI) removal by PVA/PEI nanofibers showed a pH-dependent behavior, and the maximum removal was achieved at pH 4.0. The optimum adsorption capacity for Cr(VI) was found to be 150 mg/g by fitting the Langmuir model. Removal of Cr(VI) by the nanofibers is fast (<3 h), and they could be regenerated without reducing the removal capacity. Electrostatic attraction between negatively charged Cr(VI) and positively charged nanofiber surfaces is the major mechanism for Cr(VI) adsorption. Most of the adsorbed Cr(VI) was reduced to Cr(III), showing an octahedral Cr(III) oxide structure. Amine groups in the nanofibers act as both reducing and binding sites for Cr(VI) removal. Among commonly coexisting anions, only sulfate and nitrate decreased the Cr(VI) removal by nanofibers, but did not affect the structure of adsorbed Cr. Copper could compete with Cr(VI) for complexing with amine groups, and consequently attenuate the reduction of Cr(VI). This study evaluated the application of electrospun PVA/PEI nanofibers on Cr(VI) removal in complex water matrices and provided comprehensive evidence regarding the adsorption and reduction mechanisms. Such information improves the understanding of Cr(VI) removal by electronspun PVA/PEI nanofibers, and is helpful to predict its performance in dynamic environments.