CsPbBr₃ Quantum Dots Promoted Depolymerization of Oxidized Lignin via Photocatalytic Semi-Hydrogenation/Reduction...

Due to the demanding depolymerization conditions and limited catalytic efficiency, enhancing lignin valorization remains challenging. Therefore, lowering the bond dissociation energy (BDE) has emerged as a viable strategy for achieving mild yet highly effective cleavage of bonds. In this study, a photocatalytic semi-hydrogenation/reduction strategy utilizing CsPbBr₃ quantum dots (CPB-QDs) and Hantzsch ester (HEH₂ ) as a synergistic catalytic system was introduced to reduce the BDE of C_β -O-Ar, achieving effective cleavage of the C_β -O-Ar bond. This strategy offers a wide substrate scope encompassing various β-O-4 model lignin dimers, preoxidized β-O-4 polymers, and native oxidized lignin, resulting in the production of corresponding ketones and phenols. Notably, this approach attained a turnover frequency (TOF) that is 17 times higher than that of the reported Ir-catalytic system in the photocatalytic depolymerization of the lignin model dimers. It has been observed via meticulous experimentation that HEH₂ can be activated by CPB-QDs via single electron transfer (SET), generating HEH₂ ⋅⁺ as a hydrogen donor while also serving as a hole quencher. Moreover, HEH₂ ⋅⁺ readily forms an active transition state with the substrates via hydrogen bonding. Subsequently, the proton-coupled electron transfer (PCET) from HEH₂ ⋅⁺ to the carbonyl group of the substrate generates a C_α ⋅ intermediate.