Femtosecond transient absorption spectroscopy investigation on ultrafast electron transfer in S-scheme ZnO/CdIn2S4 photocatalyst for H2O2 production and benzylamine oxidation

Photocatalytic hydrogen peroxide (H 2 O 2 ) production is a crucial process for clean energy conversion, involving the reduction of O 2 through two electrons. However, this process is often hampered by the sluggish water oxidation involving the photogenerated holes. To address this challenge, we have constructed a dual-functional S-scheme ZnO/CdIn 2 S 4 heterojunction systerm coupling the H 2 O 2 generation with a value-added benzylamine (BA) oxidation reaction. In this dual-functional photocatalytic system, photogenerated electrons in CdIn 2 S 4 efficiently reduce O 2 to produce H 2 O 2 , while photogenerated holes in ZnO selectively oxidize BA to N-benzylidenebenzylamine. Leveraging the advantages of the S-scheme heterojunction, the optimized ZnO/CdIn 2 S 4 photocatalyst displays an enhanced H 2 O 2 production rate (386 ​μmol·L −1 ·h −1 ) and BA oxidation fraction (81 ​%) than pure ZnO or CdIn 2 S 4 . Femtosecond transient absorption (fs-TA) spectroscopy confirm the ultrafast S-scheme electron transfer from the ZnO conduction band (CB) to the CdIn 2 S 4 valence band (VB) upon photoexcitation of the ZnO/CdIn 2 S 4 composite. Besides, timely depletion of VB holes in ZnO and CB electrons in CdIn 2 S 4 can accelerate the interfacial electron transfer in the ZnO/CdIn 2 S 4 S-scheme heterojunction. The innovative design of the ZnO/CdIn 2 S 4 S-scheme photocatalyst provides new insights for developing efficient dual-functional heterojunction photocatalytic systems and introduces a novel method for studying S-scheme heterojunctions using fs-TA spectroscopy. The dual-functional S-scheme ZnO/CdIn 2 S 4 heterojunction photocatalyst efficiently couples H 2 O 2 production with benzylamine oxidation, significantly enhancing photocatalytic performance. This innovative design promotes ultrafast electron transfer and provides valuable insights into the development of dual-functional photocatalytic systems.