Sustainable design of metal-lignin coordination complexes for next-generation energy and environmental applications

Lignin forms coordination complexes with multivalent metal ions, bridging lignin chemistry with metal nanomaterials for diverse applications. However, developing metal-lignin coordination complexes (MLCC) remains hindered by critical challenges, including structural heterogeneity, uncontrolled aggregation, and the complexity of tailoring coordination microenvironments. This review elucidates the advancements and emerging trends in the synthetic strategies, structural modulation and property regulation of MLCC, with a focus on the interplay between lignin and metal ion coordination. The coordination principles between lignin and metal ions for MLCC preparation via co-precipitation, self-assembly, and templating are initially discussed. Following this, emphasis is placed on the different functionalization regulations that can be conducted by lignin and metal ions in MLCC according to their different types, which mainly include micro/macro morphology regulation, and carbon material preparation. Subsequently, the applications of MLCC in energy conversion and storage, and environmental applications are discussed. Finally, the challenges and future directions of MLCC are envisioned. This review bridges lignin chemistry with metal nanomaterials, providing insights and pathways toward enhancing the performance of existing lignin-based functional materials across diverse applications.