Rapid Charge Transfer Endowed by Interfacial Ni-O Bonding in S-scheme Heterojunction for Efficient Photocatalytic H₂ and Imine Production

Cooperative coupling of H-2 evolution with oxidative organic synthesis is promising in avoiding the use of sacrificial agents and producing hydrogen energy with value-added chemicals simultaneously. Nonetheless, the photocatalytic activity is obstructed by sluggish electron-hole separation and limited redox potentials. Herein, Ni-doped Zn0.2Cd0.8S quantum dots are chosen after screening by DFT simulation to couple with TiO2 microspheres, forming a step-scheme heterojunction. The Ni-doped configuration tunes the highly active S site for augmented H-2 evolution, and the interfacial Ni-O bonds provide fast channels at the atomic level to lower the energy barrier for charge transfer. Also, DFT calculations reveal an enhanced built-in electric field in the heterojunction for superior charge migration and separation. Kinetic analysis by femtosecond transient absorption spectra demonstrates that expedited charge migration with electrons first transfer to Ni2+ and then to S sites. Therefore, the designed catalyst delivers drastically elevated H-2 yield (4.55 mmol g(-1) h(-1)) and N-benzylidenebenzylamine production rate (3.35 mmol g(-1) h(-1)). This work provides atomic-scale insights into the coordinated modulation of active sites and built-in electric fields in step-scheme heterojunction for ameliorative photocatalytic performance.