Cooperative interfacial preconditioning in an S-scheme heterojunction for CO2 photoreduction

Efficient S-scheme photocatalysis requires not only favorable band alignment but also sufficiently strong interfacial driving forces to direct photogenerated carrier migration across the junction. Local donor-acceptor (D-A) coordination and global Fermi-level equilibration are shown to cooperate in the dark to precondition interfacial energetics and thereby promote subsequent S-scheme charge transfer. A molecularly coupled heterojunction is constructed by integrating a triazine-imine covalent organic framework (TPT-COF) with ZnO quantum dots through interfacial Zn–N coordination. Spectroscopic analyses reveal that D-A-induced local electron redistribution and Fermi-level-equilibration-driven compensating charge redistribution coexist in the dark, cooperatively enlarging the effective interfacial energy offset and reinforcing the internal electric field prior to illumination. Ultrafast spectroscopy further shows that this preconditioned interface accelerates S-scheme charge transfer under light irradiation, enabling efficient spatial charge separation while preserving strong redox potentials. As a result, the optimized COF/ZnO heterojunction achieves selective CO 2 photoreduction to CH 4 without external photosensitizers or sacrificial agents. These findings identify a cooperative mechanism by which local coordination chemistry and interfacial electrostatics jointly regulate S-scheme energetics, offering a molecular strategy for designing adaptive photocatalytic interfaces for solar fuel production.