Recent trends of carbon nanotubes and chitosan composites for hexavalent chromium removal from aqueous samples

Chromium (Cr) is a hazardous metal that is extensively prevalent in wastewater. It has a life-threatening effect on human health in high quantities. From the viewpoint of adsorption-based wastewater treatment, traditional adsorbents have been studied extensively in the literature to lower the Cr level in an aqueous media, but their efficiencies are low. In this regard, carbon nanotubes (CNTs) and chitosan composites have been developed in the literature with tunable physicochemical properties to exhibit remarkable Cr removal. There are several challenges that need to be addressed to evolve CNTs and chitosan-based adsorbent treatment systems from the lab-scale to practical applications. This chapter provides coverage of the recent developments and application of CNTs and chitosan composites for the adsorptive removal of Cr to an acceptable level. Major influencing factors are highlighted, including the operational pH range, adsorbent dosage, contact time, and interference. The work also reviews the adsorption equilibrium, kinetics, and thermodynamics to delineate the adsorption mechanisms and the nature of the adsorption process. Important considerations, such as the stability and reusability of composite adsorbents and their recovery, are discussed for economic and sustainability concerns.