Simultaneous removal of Cr(VI) anions and metal cations by EDTA-crosslinking-chitosan/polypyrrole composites

Polypyrrole-based adsorbents have emerged in removing Cr(VI) from wastewater based on their reduction, chelation, electrostatic attraction and ion exchange. However, it is still a formidable challenge to remove metal cations simultaneously due to electrostatic repulsion. In fact, metal ions originating from industrial activities such as chemical manufacturing and metal electroplating are always complex and multifarious. Here, we report a EDTA-crosslinking-chitosan/polypyrrole composite (EDTA-CS/PPy) with multiple types of adsorption sites (carboxyl, hydroxyl, amino), successfully realizing simultaneous removal of Cr(VI) anions and other metal cations. The maximum adsorption capacities of Cr(VI), Cu(II), Pb(II) and Cd(II) reach up to 401.25, 59.03, 77.81 and 68.31 mg/g, respectively. The adsorption mechanism is attributed to coupling interactions of the reduction, chelation, electrostatic attraction and ion exchange between targeted metal ions and EDTA-CS/PPy, investigated by experiments and DFT theories. Notably, the adsorption capacity of EDTA-CS/PPy keeps stability after three adsorption–desorption cycles. These findings may promote potential applications of EDTA-CS/PPy adsorbents in highly efficient treatment of coexisting toxic metal ions from wastewater.