Comparative assessment of Pb (II) adsorption in different generations of magnetic-cored dendrimers: The significance of amine end group activity

Abstract

The number of amine end groups in the first (G1), second (G2), third (G3), and fourth (G4) generations of magnetic-cored dendrimers (MCD) was determined experimentally and effect on Pb (II) adsorption was investigated. Calculated end groups in different generation MCDs obtained by thermogravimetric analysis appeared an increase with successive generations, but not doubled. Decrease in end groups was due to the blocking of branches during synthesis and narrow space between end groups. Active amine end groups were also quantified via acid-base titration experiment. The active amines were increased with the generations, except for G3-MCD because of the reduced distance between end groups. However, the active amines were drastically increased in the G4-MCD because the hydrophilic amine groups were stretched in the outer space by the repulsive hydrophobic inner structure of MCD chains. Maximum Pb (II) adsorption was 44.49 mg/g (G1-MCD), 79.57 mg/g (G2-MCD), 44.35 mg/g (G3-MCD), and 116.19 mg/g (G4-MCD), respectively. They are very well correlated with the titration results, confirming the adsorption was directly affected by active amines in MCDs.