Removal of hexavalent chromium from impaired water: Polyethylenimine-based sorbents − A review

Effective treatment of water contaminated with hexavalent chromium is vital due to its genotoxic and carcinogenic nature. Considering the new stringent regulatory limits being set up for Cr(VI) in ground and surface water, it is imperative to develop efficient treatment technologies/materials for the remediation of Cr(VI)-laden impaired waters. The most common issue is the lack of selectivity of sorbents towards chromate anion and their performance in real systems. Of late, polyethylenimine (PEI) polymer-based adsorbents have gained escalating attention of researchers, owing to their redox properties and biocompatible nature. Here we review various PEI-based adsorbents developed so far to remove Cr(VI) from contaminated waters. Based on the relevant peer-reviewed articles available in the open literature, the adsorbents can be divided into six broad categories, depending on the substrate used for PEI immobilization: magnetic materials, carbon-based, silica-based, clay minerals and geomaterials, biologically-derived materials, and other hybrid composites. This review discusses the efficiency of various PEI-based adsorbents for Cr(VI) removal; facilitates a better understanding of the removal mechanism and the regeneration process of the spent adsorbents. A critical evaluation of the existing literature, research shortcomings, and future research directions required to devise improved methodologies for practical applications have also been provided. Researchers who desire to work on Cr(VI) removal, with an inclination towards developing sophisticated adsorbents, can benefit from this article.