Accumulation of Long-Lived Photogenerated Holes at Copper Yolk-Shell Heterojunctions via Heterogeneous Contraction and Reduction Strategies for Enhanced Photocatalytic Oxidation

Active holes outperform photoelectron-mediated oxygen reduction in degrading recalcitrant organics under anaerobic conditions, yet their utilization is limited by rapid charge recombination. This challenge was addressed through Cu-based yolk-double-shell microspheres (Cu/Cu₂O@C-2shell) engineered via heterogeneous contraction and reduction strategies. Work function analyses confirm Schottky junction-driven electron transfer from Cu₂O to Cu, generating an internal electric field that suppresses backflow. Density functional theory reveals Cu-mediated enhancement of near-Fermi states (Cu 3d orbitals) and a directional Cu₂O → Cu → C electron pathway, spatially isolating holes in Cu₂O. Finite-difference time-domain simulations reveal light-induced electric field gradients in the dual-shell architecture: Cu⁰-mediated localized surface plasmon resonance effect enhances surface field concentration, while hierarchical interfaces create an outward-to-inward gradient, directing electron migration inward and stabilizing oxidative holes at the surface. The optimized (Cu/Cu₂O)@C-2shell exhibits 38-fold higher tetracycline degradation under sunlight versus benchmarks, with treated water supporting Escherichia coli survival and wheat growth. This study provides a design strategy for the accumulation of long-lived holes on semiconductor photocatalysts.