Utilizing spent Li-ion batteries to regulate the π-conjugated structure of g-C3N4: a win–win approach for waste recycling and highly active photocatalyst construction

Abstract

The recycling of spent lithium-ion batteries (LIBs) has been one of the global environmental concerns due to their huge quantity and hazardous and valuable character. The existing spent LIB processing mainly focuses on element separation, which is usually complex and energy consuming and even causes new environmental issues. This study breaks through the traditional element separation and utilizes spent LIBs for photocatalytic application. Through facile one-pot sintering of a spent LiCoO₂ cathode, melamine and NH₄Cl at 530 °C, we introduced a Li–Cl–Co anion–cation to synergistically regulate the π-conjugated structure of g-C₃N₄ for enhancing its photocatalytic activity. The Li–Cl–Co anion–cation was stabilized in g-C₃N₄ through Li–N, Li–Cl, Cl–C and Co–N bonds. The Co among the adjacent tri-s-triazine units decreased the bandgap to lower the electron transition energy. The Li and Cl intercalation respectively decreases and increases the interlayer spacing, leading to a gradient decrease in the energy barrier for dramatically boosting the charge migration and separation between g-C₃N₄ layers. These special characteristics synergistically contribute to the superior photocatalytic performance. The simulated sunlight photocatalytic H₂ evolution and RhB degradation rates of this special photocatalyst were 12.6 and 15.3 times higher than those of pristine g-C₃N₄. This study avoids element separation and distinctively utilizes spent LIBs for photocatalytic application, which minimizes the environmental risks associated with recycling. Our study also reveals a synergetic concept of recycling wastes as high-efficiency photocatalysts for environmental protection.