Highly efficient and selective extraction of gold by a fluorinated imine-based covalent organic polymer†

Considering the increasing demand for gold and the scarcity of mineral resources, this study presents a promising avenue for its recovery from secondary resources. In this paper, N1,N1′-(1,4-phenylene)bis(N1-(4-aminophenyl)benzene-1,4-diamine) and 2,3,5,6-tetrafluoro-p-dibenzaldehyde were successfully prepared by the solvothermal method to synthesize a highly fluorinated covalent organic polymer with imine bonds (N-TFACOP), which can be used to recover gold ions from secondary sources. Covalent organic polymer (COP) materials have controllable structures that can be significantly improved by introducing appropriate functional groups into the structural units. The introduction of fluorine atoms with strong electron-absorbing ability into COP materials not only significantly increases the specific surface area of the materials and provides more surface active sites but also improves the chemical and thermal stability of the materials, even in strong acids and bases. The adsorption capacity for gold was further improved. At pH = 4, adsorption time of 720 min, and adsorption temperature of 45 °C, the maximum adsorption capacity of N-TFACOP for gold was as high as 2975.08 mg g⁻¹. There was no significant decrease in the adsorption rate after six cycles, which proved that the adsorption performance for gold was significantly improved by N-TFACOP. Au(III) was reduced to monomeric gold by complexation and redox reaction between the functional atom (N) and Au(III). In summary, we verified the adsorption potential of a novel covalent organic polymer for Au(III), which provides a strong reference for the recycling of the precious gold metal from secondary resources and the protection of environmental resources.