Isomeric Π Conjugated Covalent Organic Frameworks with Tunable Nitrogen Topologies for Integrated Gold Adsorption and Photoreduction

Gold recovery from electronic waste (e-waste) presents a significant materials challenge, as conventional systems lack structural tunability, exhibit poor metal selectivity, and fail to integrate adsorption and photoreduction functionalities effectively. Herein, we present a topology-guided strategy based on two isomeric π-conjugated covalent organic frameworks (COFs) (v-2D-COF-Dz and v-2D-COF-Pz), incorporating diazine (ortho-N) and pyrazine (para-N) units, respectively, for integrated gold adsorption and photoreduction. The nitrogen topology not only stabilizes the π-conjugated backbone but also significantly modulates the frameworks' optoelectronic and redox properties. Notably, v-2D-COF-Dz exhibits a markedly higher Au³⁺ adsorption capacity (2465 versus 1854 mg g^-1), attributed to enhanced interfacial electron localization and directional charge transfer to Au³⁺ centers. Both frameworks achieve over 99% gold extraction from real e-waste leachates under visible-light irradiation. Spectroscopic characterization and DFT analysis reveal that nitrogen topology governs metal coordination strength and electronic coupling, enabling precise Au-Cl bond activation. This work establishes a nitrogen-topology-directed design paradigm for light-driven, COF-based precious metal recovery systems.