Lignin‐Derived Melanin‐Like Nanosheets: Modulating the Microscopic Morphology and Photothermal Conversion Property through the Substituent Effect

Artificial melanin-like materials have attracted significant attention due to their bioactivity and photothermal conversion capability. The regulation of their morphology is essential for optimizing performance; however, this presents considerable challenges. In this study, a novel template-free approach is introduced that utilizes the Scholl reaction in conjunction with a demethylation reaction to synthesize melanin-like nanosheets. Lignin-derived triaryl-imidazole is employed as the monomer, in contrast to the commonly used phenolic monomers. The methoxy groups present in the monomers, which are derived from the original lignin structure, significantly influence the resulting polymers' characteristics, including microscopic morphology, chemical structure, optical absorption, specific heat capacity, and hydrophilicity. When veratraldehyde-derived triaryl-imidazole is utilized as the monomer, melanin-like nanosheets with a uniform thickness of 5 nm are produced, demonstrating commendable photothermal conversion performance in both bulk and suspension states, showing the potential value in solar evaporation and photothermal therapy. It is anticipated that these findings will not only facilitate the preparation of artificial melanin-like materials with tailored morphologies but also contribute to the development of lignin-derived materials with enhanced functionalities.