Post-synthetically functionalized covalent organic frameworks for highly efficient recovery of gold from leaching liquor of electronic waste

Recovery of precious metals from e-waste was of great economic and environmental significance. Herein, the spherical covalent organic frameworks (COF-V) were constructed by the Schiff base reaction between 1, 3, 5-tris (4-aminophenyl) benzene and 2, 5-divinylterephthalaldehyde, followed by post-synthetic modification using mono-(6-mercapto-6-deoxy)-β-cyclodextrin (S-β-CD) and dithiothreitol (DTT) for recovery of gold from e-waste. Multi-farious microscopic and spectroscopic techniques were used to explore the micromorphology and elemental composition of all the materials. Meanwhile, the response surface method was used to optimize the experimental parameters to improve the adsorption performance of Au(III). The functionalized spherical COFs exhibited excellent Au(III) adsorption abilities with maximum adsorption capacities of 652.6 mg/g and 820.8 mg/g for COF-V-DTT and COF-V-S-β-CD, respectively. The impressive properties were due to the synergistic adsorption effect of the grafted hydroxyl and sulfhydryl groups in appropriately sized ordered pores. The spectral analysis demonstrated that Au(III) was firstly adsorbed on the adsorbents by coupling with the S atom, and then in situ reduced to Au(0) by hydroxyl groups. Moreover, two COFs materials also exhibited an excellent selectivity in the actual gold-containing waste liquid. Thus, this study would provide an efficient and economical way to recovery Au(III) from wastewater.