Covalent organic frameworks constructed by flexible alkyl amines for efficient gold recovery from leaching solution of e-waste

Recovering precious metals from electronic equipment waste involves significant environmental and economic benefits. In this paper, a covalent organic framework, named as TpTsc COF, was synthesized by using flexible alkyl amine thiosemicarbazide (Tsc) and 1,3,5-triformylphloroglucinol (Tp) as precursors for extracting gold from actual electronic waste. The results show that it has favorable selectivity, high recycling and groundbreaking adsorption capacity (4400.23 mg g-1). Such excellent adsorption capacity can be attributed to the improved crystallinity by irreversible enol-to-tautomerism of Tp, the abundant functional group sites in Tsc, and the efficient reduction of gold by thiourea. The adsorption process can be well fitted with the pseudo-secondorder kinetic model and Langmuir mode, which is characterized by the coordination between Au (III) and S, N, O atoms in COF, as well as the electrostatic interaction between protonated amino groups and AuCl4- in acidic system. The advantages of this feasible method facilitate effective gold recovery from low-cost electronic waste.