Lignin oxidative depolymerization on graphitic carbon nitride - explore the cleavage of β-5 linkage

As Net Carbon Zero and the development of the circular economy become critical global environmental issues, developing alternative green energy and chemical resources for fossil fuels are an area of significant research activity. Lignocellulosic biomass as the most abundant biomass throughout the world has aroused much attention as a green energy and value-added product source. As one of lignocellulosic biomass components, lignin which is comprised of different aromatic monomers, is a potential feedstock for value added chemical production. However, the method and mechanism of the cleavage of linkages between monomers to obtain high-value monomers still requires much investigation. Therefore, this study focuses on photocatalytic conversion of a β-5 lignin model compound. In this study it was found that a higher yield of aromatic products were obtained from a β-5 lignin model compound which underwent photocatalytic conversion over a carbon nitride catalyst compared to P25. The final conversion products of β-5 model compound were identified by GC-MS. According to GC-MS analysis, the cleavage occurs at the carbon-carbon bond between the benzene ring and the α-carbon, producing two aromatic monomers. The above results reveal for the first time the products and possible mechanism of photocatalytic transformation of β-5 model compounds under carbon nitride.