Graphene oxide/polydopamine modified montmorillonite/carboxymethyl chitosan composite aerogel for efficient removal of Pb²⁺, Cu²⁺, and Cd²⁺: Adsorption behavior, mechanism and DFT study

A novel ternary composite aerogel was prepared from graphene oxide (GO), polydopamine-modified montmorillonite (PDA-MMT), and carboxymethyl chitosan (CMCS) for the removal of Pb²⁺, Cu²⁺, and Cd²⁺. Adding PDA-MMT and CMCS enhances GO aerogels' mechanical properties and adsorption properties. GO/PDA-MMT/CMCS with rich pore structure and many exposed active sites, exhibited outstanding Pb²⁺, Cu²⁺, and Cd²⁺ adsorption capacities with Q_m of 465.12, 354.61, and 317.46 mg/g, respectively. Synergistic interaction between GO, PDA-MMT, and CMCS enhances adsorption properties. The pseudo-second-order kinetics and Langmuir models better describe the adsorption process of GO/PDA-MMT/CMCS. The adsorption is mainly monomolecular chemisorption, primarily controlled by chemisorption. The GO/PDA-MMT/CMCS exhibited excellent ionic interference and cyclic stability resistance. The removal rate was still > 81 % after 5 cycles. Fixed-bed and industrial wastewater adsorption verified the practicality of GO/PDA-MMT/CMCS. DFT calculations revealed the minimum adsorption energy for Pb²⁺ (-3.77 Ha), signifying a more stable binding between Pb²⁺ and the GO/PDA-MMT/CMCS. The adsorption mechanism is mainly chelation, ion exchange, synergistic effect, electrostatic attraction, and pore adsorption. The aerogel has high adsorption performance, low cost, and easy separation, which is favorable for its application in wastewater treatment.