TiO2 as an interfacial-charge-transfer-bridge to construct eosin Y-mediated direct Z-scheme electron transfer over a Co9S8 quantum dot/TiO2 photocatalyst

Abstract

The direct Z-scheme heterojunction is an ideal system for photocatalytic H₂ production, which can efficiently separate photogenerated charges and maintain stronger redox ability. Herein, for the first time, a novel direct Z-scheme Co₉S₈ quantum dots/TiO₂ (Co₉S₈ QDs/TiO₂) photocatalytic system was constructed in the presence of eosin Y (EY) with TiO₂ as an interfacial-charge-transfer-bridge. The amorphous Co₉S₈ QDs were successfully anchored on the surface of TiO₂via an in situ hydrothermal method. The spatial behavior of photocarriers was effectually regulated based on the bandgap-matching theory, which greatly decreased the recombination of the electrons and holes of Co₉S₈. Most importantly, TiO₂ serving as an interfacial-charge-transfer-bridge can promote the electron transfer of excited-state EY to the valence band of Co₉S₈ QDs to scavenge its photogenerated holes, causing Z-scheme charge transfer in the intimate interface between Co₉S₈ QDs and TiO₂. As a result, a maximum H₂ production rate of 2813.9 μmol h⁻¹ g⁻¹ was achieved over the 20%Co₉S₈ QDs/TiO₂ heterojunction, which is 3.3 and 197.5 times greater than that of Co₉S₈ QDs and TiO₂, respectively. A high AQE of 37.4% was obtained at 470 nm for 20%Co₉S₈ QDs/TiO₂. The Z-scheme charge transfer mechanism was confirmed by comparative experiment analysis, time-resolved fluorescence (TRPL) decay, and in situ Pt photodeposition. The present work provides a novel approach to constructing Z-scheme photocatalytic systems for efficient artificial solar energy conversion.