Efficient removal of heavy metal ions and organic dyes with cucurbit [8] uril-functionalized chitosan

The development of a high-efficiency adsorption material is important for the simultaneous elimination of heavy metal ions and organic pollutants from wastewater. In the present work, a novel material was synthesized by grafting functionalized cucurbit [8] uril (CB[8]) onto chitosan (CS) chains via a CNC covalent bond (CB[8]-CS). This as-prepared material presented an unprecedented adsorption capacity. The maximum adsorption capacities (q_m) were 1622.7 mg/g, 1172.7 mg/g, 1361.9 mg/g and 873.6 mg/g for the adsorption of reactive orange 5 (RO5), acidic blue 25 (AB25), reactive yellow 145 (RY145) and Pb²⁺ ions, respectively, which are far higher than the reported data. The simultaneous co-adsorption of dye and a heavy metal ion was tested with a mixed solution of 200 mg/L RO5 dye and Pb²⁺ ion, and the removal rates were 97% and 70% for RO5 and Pb²⁺, respectively. The adsorption mechanism was explored by means of the IR spectrum and the UV-vis diffuse reflection spectrum (DRS) together with theoretical calculations. The adsorption of dyes was mainly driven by the strong interaction between dye molecules and the hydrophobic cavity of CB[8], and the Pb²⁺ adsorption was mainly driven by the coordination of Pb²⁺ with the carbonyl of the CB[8] port and the amino group of chitosan. The ultrahigh adsorption capacity allows the use of CB[8]-CS as potential adsorbent for the simultaneous removal of heavy metal ions and organic dyes from aqueous solution.