Recovery of silver and gold quantum dots from wastewater via coagulative adsorption onto CoFe2O4 based magnetic covalent-organic framework to generate efficient nanocatalysts for degradation of doxorubicin drug

Abstract

Quantum dots (QDs) are recognized as significant environmental hazardous pollutants owing to their increasing demands in several industries. As a result, removing QDs from wastewater is an interesting topic that drew attention of scientists nowadays. In this research, an innovative material based on the combination of magnetic covalent organic frameworks (MagCOFs) and aminated agar-fava bean peels biochar hydrogel is presented as a nanosorbent for adsorptive removal of silver quantum dots (Ag-QDs) and gold quantum dots (Au-QDs). Morphology and chemical structure of the nanosorbent was identified by SEM-EDX, XRD, FT-IR and XPS analyses. The EDX analysis of MagCOF@Aminated agar-FBP biochar nanosorbent confirmed characteristic percentages of C (46.52%wt), N (22.22%wt), O (22.50%wt), Fe (1.98%wt), Co (0.86%wt). The XPS results of the assembled nanosorbent referred to the presence of B, C, N and O with their characteristic peaks at 191.56 eV, 285.92 eV, 400.25 eV and 532.27 eV, respectively. QDs removal was optimized by controlling several factors such as pH, adsorbent dosage, shaking time, initial QDs concentration, temperature and ionic strength. At optimum conditions, 97.6 % and 100.0 % removal efficiencies were achieved for Ag/Au-QDs subsequently through a chemical adsorption process following pseudo-second order kinetics. Additionally, the theoretical qe = 121.95 and 125.00 mg g−1 for Ag-QDs and Au-QDs, respectively were perfectly fitted with those detected experimentally as 121.95 and 124.18 mg g−1 for the same two QDs. The developed nanomaterial was identified to retain good stability towards Ag-QDs and Au-QDs after 5 successive adsorption/regeneration cycles with only 3.5 % and 4.5 % drop in their activity, respectively. Furthermore, thermodynamic studies proved the spontaneity of the exothermic adsorption process. Additionally, several industrial wastewater samples were collected and used to prove the applicability of proposed process. Recovered and immobilized Ag/Au-QDs on the surface of MagCOF@Aminated agar-FBP biochar were reused as microwave degradation nanocatalysts for doxorubicin (DOX) drug, providing percentage degradation reaching 93.15 % and 96.68 % in <10 min for Ag/Au-QDs, respectively.