Three-Dimensional Covalent Organic Frameworks Containing Diverse Nitrogen Sites for Gold Adsorption

As the study progresses, it becomes more significant to explore the effect of specific active sites in covalent organic frameworks (COFs) on the gold adsorption process. Meanwhile, emerging 3D COFs are potential candidates for the adsorption of gold due to their rich pore and cage structures. In this work, to study the effect of the introduction and position of aromatic Ns on the gold capture, we synthesized three 3D COFs which have good selectivity, immunity to interference, reproducibility, and the potential to recover gold from e-waste. Compared to the COF containing only imine bonds as a blank, the introduction of triazine and pyridine rings resulted in a higher maximum adsorption capacity (2081 mg/g) and a faster adsorption rate (within 10 min), respectively. Theoretical calculations show that the presence of the triazine ring enhances the reduction of Au3+ by COF, while the synergistic effect of pyridine N and imine bonding shortens the adsorption time of gold. This work reveals the great potential of 3D COFs for gold adsorption and the roles played by the different types of aromatic Ns on gold capture, providing a reference for enhancing the adsorption performance of 3D COFs on gold.