Progress and challenges in heterocyclic polymers for the removal of heavy metals from wastewater: a review

Abstract

Water contamination by heavy metals has emerged as a global environmental problem. Their toxicity, non-degradability, and persistent nature make them a serious threat to human health, flora, and fauna. Therefore, several techniques have been developed for the removal of these pollutants from wastewater. Recently, linear aromatic polymers have received increasing attention for wastewater treatment due to the presence of various heterocyclic moieties containing electron-donating atoms such as nitrogen, oxygen, or sulfur on their backbone, which can be easily coordinated with metals, resulting in excellent affinity for heavy metals. This review article is specifically devoted to providing an overview of the various linear-architecture heterocyclic polymers that have been synthesized to be used as adsorbent phases for the removal of heavy metals from wastewater over the past fifteen years. The importance of incorporating heterocyclic units as efficient chelating sites for ion binding is highlighted. The adsorption mechanisms of different aromatic polymers are presented; their adsorption isotherms can primarily be modeled with the Langmuir model and their kinetics follow a pseudo-second-order kinetic model. The ways to improve the adsorption capacities of the linear aromatic polymers by increasing their specific surface area are discussed in the perspective paragraph, along with strategies to improve their reusability by choosing the proper acidic washing step.