Magnetite modified amino group based polymer nanocomposites towards efficient adsorptive detoxification of aqueous Cr (VI): A review

Chromium exists in aqueous environment mainly in two forms namely hexavalent [Cr (VI)] and trivalent [Cr (III)]. Cr (VI) is acutely toxic, mutagenic and carcinogenic whereas Cr (III) is about 1000 times less toxic and is a micronutrient for living organisms. It is, therefore highly desirable for effective capture of aqueous Cr (VI) and its subsequent detoxification (reduction) to Cr (III). Magnetite modified amino group based polymer nanocomposites (MNHPCs) have good affinity with adsorptive detoxification of Cr (VI). We have herein assessed the performance of these adsorbents based on surface morphology, textural properties, availability of -NH- and -N= groups, adsorption parameters and separation ability. At first, the synthesis strategies that govern surface morphology and textural properties are briefly discussed. The adsorption parameters such as pH, initial Cr (VI) concentration, adsorbent dosages, contact time and temperature were then reviewed. We then have systematically overviewed kinetics, equilibrium and thermodynamics of adsorption which revealed its chemical nature. Thereafter, the plausible mechanism for adsorptive detoxification of Cr (VI) was described. Basically it involves electrostatic attraction between Cr (VI) species and positively charged surface of MNHPCs followed by uptake through ionic interaction, ion exchange and coordination interaction, after which the adsorbed Cr (VI) is partially reduced to Cr (III). Facile separation ability with excellent recyclability of this class of adsorbents was then highlighted. Finally, the challenges faced by these adsorbents are addressed and future directions of research were depicted along with conclusion. (C) 2021 Elsevier B.V. All rights reserved.