Nanoarchitectonics of S-scheme CdS-SH QDs/Bi2MoO6 heterojunction for boosted photocatalytic lignin biomass conversion: Interplay of singlet oxygen and interfacial engineering

Photocatalytic depolymerization of lignin biomass into high-quality fuels and value-added chemicals shows great potential for environmental protection. However, its efficiency is affected by stringent depolymerization conditions and a complex depolymerization process. Herein, CdS-SH QDs/Bi2MoO6 S-scheme heterojunctions with strong interfacial interactions were successfully fabricated trying to give a "fatal blow" to the crucial C beta-O bond in lignin. The formation of Bi-S bonds at the interface enhances the activation of photogenerated charge carriers, leading to the production of singlet oxygen (1O2), which effectively reduces the bond energy of C beta-O bonds in lignin. On the optimized composite photocatalyst, the total conversion of PP-ol was about 100 % with rising oxygen concentration, and phenol and acetophenone (AP) were the main products with yields of 90 % and 93 %, respectively. By cleaving the C beta-O bond of alkali lignin isolated from Pinus massoniana under air, the yield of vanillin at CdS-SH QDs/Bi2MoO6 was 26.6 mg/glignin, which was 70 and 3.52 folds higher than that of Bi2MoO6 and CdS-SH QDs, respectively. Density-functional theory (DFT) calculations, in-situ X-ray photoelectron spectroscopy (XPS) and in-situ electron paramagnetic resonance (EPR) evidenced the S-scheme charge migration pathways in CdS-SH QDs/Bi2MoO6 during the photocatalytic reaction. This work provides a new perspective on designing photocatalysts capable of efficiently depolymerizing lignin in real environments.