Recycling Spent LiCoO₂ Battery as a High-efficient Lithium-doped Graphitic Carbon Nitride/Co₃O₄ Composite Photocatalyst and Its Synergistic Photocatalytic Mechanism

The ever-increasing quantity of spent lithium-ion batteries (LIBs) is both a potential environmental pollutant and a valuable resource. The spent LIBs recycling mainly aimed at the separation of valuable elements. Some issues still exist in these processes such as high energy consumption and complex separation procedures. This study avoided element separation and proposed a facile approach to transform spent LiCoO₂ electrode into a lithium (Li)-doped graphitic carbon nitride (g-C₃N₄)/Co₃O₄ composite photocatalyst through one-pot in situ thermal reduction. During the thermal process, melamine served as the reductant for LiCoO₂ decomposition and the raw material for g-C₃N₄ production. Li was in situ doped in g-C₃N₄ and the generated Co₃O₄ was in situ integrated, forming a Li-doped g-C₃N₄/Co₃O₄ composite photocatalyst. This special composite exhibited an enhanced photocatalytic performance, and its photocatalytic H₂ production and RhB degradation rates were 8.7 and 6.8 times higher than those of g-C₃N₄. The experiments combined with DFT calculation revealed that such enhanced photocatalytic efficiency was ascribed to the synergy effect of Li doping and Co₃O₄ integrating, which extended the visible light absorption (450–900 nm) and facilitated the charge transfer and separation. This study transforms waste into a high-efficient catalyst, realizing high-valued utilization of waste and environmental protection.