Unlocking the photothermal conversion capacity of lignin and lignin-derived materials

[Display omitted] •Lignin is a highly promising green renewable photothermal conversion agent.•The species and structure of industrial waste lignin was systematically summarized.•The photothermal conversion mechanisms of lignin were comprehensively analyzed.•Lignin-derived photothermal technology are described accompanied by insights. Lignin is the most prevalent polyphenolic organic solid waste generated by the pulping and biorefining industries. It confers upon woody biomass a remarkable combination of physical, chemical, and biological resilience, while simultaneously exhibiting considerable potential for photothermal conversion. In recent years, the utilization of technical lignin and lignin by-products to develop photothermal materials has emerged as a research hotspot. This review introduces the industrial separation processes and characterization of different types of lignin, highlighting the chemical structures of lignin and its derivatives linked to their photothermal conversion mechanisms. The evaluation pathways for photothermal conversion are summarized and critically assessed, as guided by mathematical descriptions of best practices in lignin-derived materials. This review covers and reflects on recent and emerging advances in materials and energy sciences that demonstrate how lignin can be utilized to maximize solar-to-thermal conversion and versatility in desalination, electricity generation, therapy, and intelligent and environmentally friendly building materials. Finally, the challenges and proposed future directions for the development of lignin-derived photothermal materials are identified with the objective of challenging the prevailing notion that lignin is merely an organic solid waste.