BiOBr/g-C3N4 heterojunction for aqueous-visible photocatalytic recovery of palladium from waste palladium/carbon catalyst

Photocatalytic dissolution represents a promising alternative to conventional, highly toxic, and energy-intensive palladium (Pd) recovery technologies. However, achieving efficient recovery under visible-light illumination in aqueous solution remains a challenge. Herein, we constructed a visible-light-responsive heterojunction photocatalyst by in-situ growing BiOBr nanosheets on nanostructured g-C 3 N 4 . Under simulated sunlight irradiation (AM 1.5G, 100 mW/cm 2 ), the optimized BiOBr/g-C 3 N 4 achieved 88 % Pd dissolution from waste palladium/carbon catalyst (w-Pd/C) within 3 h, outperforming single-component catalysts. Free radical trapping experiments and electron spin resonance (ESR) analysis revealed that efficient separation and migration of photogenerated charge carriers at the heterojunction interface generated abundant reactive species. The photogenerated e − reacted with O 2 to produce •O 2 − , while h + reacted with H 2 O to generate •OH. Simultaneously, Br − was oxidized by h + and •O 2 − to form bromine radicals (•Br), which then combined to form Br 2 . These reactive species (•O 2 − , •OH, and Br 2 ) accumulated on the w-Pd/C surface and collectively promoted the oxidative dissolution of Pd. This study highlights the potential of combining heterojunction engineering with halogen coordination in sustainable metal recovery, providing novel insights and technical support for the green recovery of precious metals, with significant implications for environmental protection and resource cycling.