In-Situ-Constructing Covalent Triazine Framework Carbon Quantum Dot-Ni-MOL Composite Photocatalysts with a Sandwich Structure and Their Application in the Selective Cleavage of C–C Bonds in Lignin

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Enhancing the selective depolymerization of lignin and improving the yield of aromatic monomers obtained from sustainable biomass have been increasingly regarded as a valuable strategy. In this work, a set of newly designed photocatalytic materials was constructed by integrating nickel-based metal–organic layers (Ni-MOL) together with carbon quantum dots doped with phosphorus (P-CQDs) into covalent triazine frameworks (CTFs) through an in situ compositing approach. Among all of the photocatalysts with varying phosphorus doping levels, CNC2.0 revealed the highest yield of benzaldehyde and benzoic acid (96.6 and 59.84%, respectively). Mechanism studies revealed that coupling CTFs with Ni-MOL markedly increased the number of active sites. The introduction of P-CQDs increased the photogenerated electron transport channel and reduced the electron transport resistance. Moreover, P-CQDs were capable of efficiently tuning the electronic characteristics of the composite, thereby enabling the controlled generation of specific free radicals for C–C bond scission. This work offers a facile strategy for fabricating photocatalysts that can be applied to biomass valorization.