Study on the competitive adsorption and correlational mechanism for heavy metal ions using the carboxylated magnetic iron oxide nanoparticles (MNPs-COOH) as efficient adsorbents

In this study, carboxylated magnetic iron oxide nanoparticles (MNPs-COOH) with well-formed nanostructure and magnetic recoverability were prepared successfully via a simple grafting method, and their adsorption competitiveness and differences for different heavy metal ions were generally explored both in single and mixed systems. The results showed that the Cd2+ adsorption demonstrated the strongest resistivity to the effects from exogenous factors with the tightest binding with the carboxyl groups on the MNPs-COOH surface. Besides, the competitive adsorption and multicomponent desorption experiments reflected that the affinity and adsorption priority of the as-synthesized MNPs-COOH for different heavy metal ions were hierarchical and followed the rank of Cd2+ > Cu2+ > Pb2+ > Ni2+, resulting from the disparity of the proportion and intensity of the inner-sphere complexation between heavy metals and the MNPs-COOH. It is hoped that our work could offer effective guidance for the MNPs-COOH application in the wastewater treatments involving various heavy metal contaminants in the future.