Anion-Regulated Ionic Covalent Organic Frameworks for Highly Selective Recovery of Gold from E-Waste

Abstract

The existing electronic waste (e-waste) and leaching solutions generated by industries accumulate significant amounts of gold (Au), even in excess of those in natural minerals. Therefore, the recycling of Au is extremely significant for the potential sustainability of chemical industry. By designing ionic covalent organic frameworks (COFs), here we synthesize a series of Ionic-COF-X (X=Cl⁻, Br⁻, AcO⁻, and SO₄²⁻) by anion regulation strategy and further explore their adsorption performance towards Au recovery. All these ionic COFs exhibit ultrahigh gold adsorption efficiency and excellent regeneration. Moreover, anion regulation could indeed affect the Au capture performance. In particular, when Cl⁻ ions serve as counter ions, the Au capacity of Ionic-COF-Cl could reach 1270.8 mg g⁻¹. Moreover, in the actual CPU leaching solution test, the selectivity of Ionic-COF-Cl towards Au³⁺ ion hits 39000 and 4600 times higher than that of Cu²⁺ and Ni²⁺ ions, respectively, suggesting that the Ionic-COF-Cl is a promising material for highly selective recovering gold from actual e-waste. DFT calculations further reveal that counter ions can regulate the adsorption affinity of ionic COF framework toward Au. In short, this work provides a useful anion regulation strategy to design ionic COFs as a promising platform for gold selective recovery from actual e-waste.