The removal of heavy metal ions from wastewater/aqueous solution using polypyrrole-based adsorbents: a review

Water pollution caused by heavy metal ions is becoming a serious threat to human and aquatic lives day by day. Therefore, the treatment of heavy metal ions is of special concern for environmental scientists and engineers. Historically, various methods, such as physical and chemical precipitation, ion-exchange, reverse osmosis, membrane filtration, electrochemical treatment, solvent extraction, and adsorption, have been widely studied for the removal of these metal ions from aqueous/wastewater. However, over the past few decades, conducting polymer-based adsorbents have received considerable attention owing to their potential applications for different heavy metal ions especially Cr(VI), Zn(II), and Pb(II). Among the various conducting polymers, polypyrrole (PPy) based adsorbents play a major role for the removal of various heavy metal ions due to their ease of synthesis, biocompatibility and redox properties. The current review has mainly focused on the physico-chemical properties, adsorption characteristics and mechanism of different polypyrrole-based adsorbents, including PPy/biosorbents, PPy/Fe3O4 nanocomposites, PPy-polyaniline nanofibers, PPy-graphene nanocomposites, exfoliated PPy-organically modified clay nanocomposites, and hierarchical porous PPy-nanoclusters, as well as their applications towards the removal of heavy metal ions.