Thiazole-linked covalent organic frameworks for enhanced photoreductive gold recovery from e-waste

Abstract

In this work we developed two different thiazole-linked Covalent Organic Frameworks (COFs) from their imine analogues for the recovery of gold from electronic waste. These gold ions are reduced through a dual-function mechanism: either directly by the COF framework itself or by photocatalytically generated electrons under light irradiation. Two COF systems were investigated: one based on pyrene (Tfpy-PDA) and another on a triazole-triazine core (TTT-TAPB). Initially synthesized with imine linkages, these COFs underwent a post-synthetic modification to convert the imine bonds into more robust thiazole rings. This transformation introduced sulfur atoms, significantly enhancing the gold adsorption performance, recyclability, stability and photophysical properties. Specifically, the thiazole-linked TTT-TAPB-S COF achieved a very high gold adsorption capacity of 3533 mg g⁻¹ in dark conditions. Upon light irradiation, the adsorption capacities increased for both imine and thiazole variants, reaching a record high of 7980 mg g⁻¹ for the thiazole-linked Tfpy-PDA-S COF. Demonstrating practical utility, these materials effectively removed up to 98% of gold from complex CPU waste leachates with high selectivity and exhibited excellent stability and recyclability.