Transformation of lignin into value-added products via thermal cracking, electrolysis and photolysis

As a rich and renewable polymer, lignin is difficult to fully utilise like cellulose and hemicellulose due to its complex structure. Therefore, using modern technology to modify the structure of lignin is effective into starting materials. Catalytic degradation is currently a promising method for the valuable lignin products, which can provide highly functionalized monomers and oligomers as other materials, realise the development of lignin resources, make lignin a high value-added product, and provide the possibility of replacing fossil fuels in the chemical and pharmaceutical industries, which is benefit to the circular economy in the future. Here, we conclude the nanocatalytic modification methods of lignin, including biocatalysts, electrocatalysts, and photocatalysts, and briefly discuss the reaction mechanism of the catalytic process, with a focus on the effective decomposition of lignin into organic solutions and small molecule complexes in thermal cracking reactions. This review provides a reference for the study of the value of lignin in various applications.