(92g) Disulfide Functionalized Covalent Organic Frameworks (DS-COFs) for Selective Recovery of Au3+ Ions from Secondary Wastes.

The relevance of recovering gold (Au) from secondary sources such as e-waste leachates has become increasingly crucial due to the limited supply of this precious metal and the growing rate of e-waste generation. Herein, a covalent organic framework (DS-COF) containing two sulfur-bearing units was synthesized by the Schiff base reaction, utilizing benzene-1,3,5-tricarboxaldehyde and 4,4-diaminophenyl disulfide as precursors. This framework was designed for the purpose of extracting gold from leachates of electronic wastes. Various characterization techniques, such as XRD, FTIR, TGA, SEM-EDS, BET surface area and pore size distribution, and EA, confirm the effective synthesis of DS-COF. The results obtained from transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) provide evidence that the binding mechanism of Au³⁺ on DS-COF involves both capture and reduction of the Au³⁺ ions. The adsorption studies on DS-COF demonstrate a maximum adsorption capacity of 691 mg/g. The data obtained from these experiments align well with the pseudo-second-order kinetic model and Langmuir adsorption isotherm. The results of the selectivity analysis confirm that Au³⁺ exhibits a significantly greater affinity and distribution on DS-COF compared to other Mn⁺ cations, with a KD value of 238.23 L/g for Au³⁺, whereas the KD values for the other Mⁿ⁺ cations are less than 0.01. When compared to the other metal ions, DS-COF shows a significant preference or separation factor for Au³⁺, with an α value of 3150–628,118 times higher than the competing metal ions. Due to its stability and capacity to be processed multiple times in an acidic environment, it could be a suitable option for practical usage in selectively recovering Au³⁺ from complicated electronic waste matrices.