Polyethylenimine-functionalized graphene quantum dots for Cd²⁺ ion adsorption

In recent years, green, environment-friendly and low-cost effective adsorbents have attracted great attention to remove heavy metal ions (HMIs) from wastewater. Graphene quantum dots (GQDs) are widely used as adsorbents to remove HMIs from wastewater. However, GQDs have a low adsorption efficiency and their adsorption effects are not always high enough. Herein, PEI functionalized GQDs (GQDs-PEI) were elaborately prepared for removing Cd2+ ions from wastewater. The mass ratio of GQDs and PEI and the molecular weight of PEI were optimized. The efficacies of GQDs-PEI concentration, Cd(2+ )ion concentration, pH, and adsorption time were also studied. The GQDs-PEI shows ultrahigh adsorption capacity for Cd2+ ions, with the highest adsorption of 357.1 mg g(-1). The results demonstrated that GQDs-PEI can be easily regenerated and has strong adsorption efficiency to remove Cd2+ ions from wastewater, thus opening several opportunities for the use of nanoparticles in environmental science and technology.