TiO2 as an interfacial-charge-transfer-bridge to construct Eosin Y-mediated direct Z-scheme electron transfer over Co9S8 quantum dots/TiO2 photocatalyst
Direct Z-scheme heterojunction is an ideal system for photocatalytic H2 production, which can efficient separation photogenerated charges and maintain stronger redox ability. Herein, 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 for the first time. The amorphous Co9S8 QDs was successfully anchored on the surface of TiO2 via in-situ hydrothermal method. The spatial behavior of photocarriers was effectually regulated based on the bandgap-matching theory, which is greatly decreased the recombination of electrons and holes of Co9S8. Most importantly, the TiO2 serve 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, forming Z-scheme charge transfer in the intimate interfacial between Co9S8 QDs and TiO2. As a result, a maximum H2 production rate of 2813.9 μmol h−1g−1 is achieved over 20%Co9S8 QDs/TiO2 heterojunction, which is 3.3 and 197.5 times greater than that of Co9S8 QDs and TiO2, respectively. And a high AQE of 37.4% is obtained at 470 nm for 20%Co9S8 QDs/TiO2. The direct Z-scheme charge transfer mechanism is evidenced by comparative experiment analysis and time-resolved fluorescence (TRPL) decay. The present work has provided a novel approach to construct Z-scheme photocatalytic systems for efficient artificial solar energy conversion.