Targeted O2 Activation over Cyano-Functionalized g-C3N4 Enhances Visible-Light Photocatalytic Dissolution of Precious Metals

Photocatalytic dissolution of precious metals (PMs) relies critically on the generation of specific reactive intermediates; however, the rational control of radical species in visible light remains challenging. Herein, we introduced the cyano (−CN) group into g-C3N4 (denoted as g-C3N4–CN), achieving a remarkable enhancement in the dissolution efficiency of precious metals under visible light. The −CN group not only promotes the visible-light absorption of g-C3N4–CN, but also facilitates the separation of photogenerated charges. The electron paramagnetic resonance (EPR) spectroscopy further demonstrates that g-C3N4–CN instantaneously generates superoxide radicals (O2•–) via efficient oxygen reduction while simultaneously promoting the rapid production of alkyl radicals (R•) through solvent oxidation. In contrast, pristine g-C3N4 exhibits a sluggish generation of all radical species. The distinct radical generation kinetics of g-C3N4–CN is identified as the key driver for its superior dissolution efficiency, enabling precious-metal recovery rates by 2–4 times and establishing a radical-targeted strategy for sustainable photocatalysis.