Microwave-assisted melamine-based polyaminals and their application for metal cations adsorption

Abstract

Three new cross-linked melamine-based polyaminal networks containing phenyl (MA-iPh), pyridine (MA-Py) or thiophene (MA-Th) moieties were easily prepared by microwave irradiation (MW) in shorter reaction times (between 1.5 and 4 h) than conventional heating (72 h). The networks showed high nitrogen content (27–37%), specific surfaces between 34 and 424 m2g−1 and high thermal stability (300 °C). The adsorption capacity of these polyaminals was determined over different toxic metals such as Cr(VI), Cu(II), Cd (II) and Pb(II) at different pH. The results showed greater chromium adsorption capacity in acid medium (pH 2), while the divalent cations were mainly adsorbed at pH 5. MA-Py that displayed the highest nitrogen content (37%) and highest specific surface area (424 m2g−1) also showed the highest adsorption capacities of this series, with values of 27.22, 26.42, and 53.13 mg/g for Cr(VI), Cd(II) and Pb(II); respectively. Additionally, MA-Py and MA-iPh with adsorption capacities of 29.12 and 25.02 mgg−1 for Cr(VI) and Cd(II), were competitive in terms of adsorption capacities regarding commercial ion exchange-resins which shown adsorptions in the range 13.7–21.3 mg/g.