Photoredox-Promoted Co-Production of Dihydroisoquinoline and H₂O₂ over Defective Zn₃In₂S₆

One of the most sustainable and promising approaches for hydrogen peroxide (H₂O₂) production in a low-cost and environment-friendly way is photosynthesis, which, however, suffers from poor carrier utilization and low H₂O₂ productivity. The addition of proton donors such as isopropanol or ethanol can increase H₂O₂ production, which, unfortunately, will inevitably elevate the entire cost while wasting the oxidizing power of holes (h⁺). Herein, the tetrahydroisoquinolines (THIQs) is employed as a distinctive proton donor for the thermodynamically feasible and selective semi-dehydrogenation reaction to highly valuable dihydroisoquinolines (DHIQs), and meanwhile, to couple with and promote H₂O₂ generation in one photoredox reaction under the photocatalysis by dual-functional Zn₃In₂S₆ photocatalyst. Surprisingly, the suitably defective Zn₃In₂S₆ offers an excellent and near-stoichiometric co-production performance of H₂O₂ and DHIQs at unprecedentedly high rates of 66.4 and 62.1 mmol h^-1 g^-1 under visible light (λ ≥ 400 nm), respectively, which outperforms all the previously available reports even though sacrificial agents were employed in those reports. Additionally, photocatalytic redox reaction mechanism demonstrates that H₂O₂ can be generated through multiple pathways, highlighting the synergistic effect among ROS (·O₂^- and ¹O₂), h⁺ and proton donor, which has been ignored in previous studies.