Eco-friendly ß-cyclodextrin and linecaps polymers for the removal of heavy metals

Environment-friendly nanosponges, having a high content of carboxyl groups, were synthesized by crosslinking ß-cyclodextrin and linecaps, a highly soluble pea starch derivative, with citric acid in water. Additionally, pyromellitic nanosponges were prepared by reacting ß- cyclodextrin and linecaps with pyromellitic dianhydride in dimethyl sulfoxide and used in comparison with the citric nanosponges. After ion-exchange of the carboxyl groups H+ with sodium ions, the ability of the nanosponges to sequester heavy metal cations was investigated. At a metal concentration of 500 ppm, the pyromellitate nanosponges exhibited a higher retention capacity than the citrate nanosponges. At lower metal concentrations (≥50 ppm) both the citrate and the pyromellitate nanosponges showed high retention capacities (up to 94% of the total amount of metal), while, in the presence of interfering sea water salts, the citrate nanosponges were able to selectively adsorb a significantly higher amount of heavy metals than the pyromellitate nanosponges, almost double in the case of Cu2+.