Carbon quantum dots bridged TiO2 and Cd0.5Zn0.5S film as solid-state Z-scheme photocatalyst with enhanced H2 evolution activity

Traditional type II heterojunction photocatalyst usually has excellent activities due to the improved charge transfer between the matched band structures of each component, but this is also accompanied by reducing the oxidation–reduction capability of electrons and holes. Z-scheme system is demonstrated to be effective on maximizing the advantages of each photocatalyst. In this work, a novel Z-scheme heterojunction photocatalyst containing TiO2 nanofilm, Carbon Quantum Dots (CQDs) and Cd0.5Zn0.5S (CZS) nanoparticles (CZS/C/TiO2 nanofilm) was fabricated by hydrothermal method and an in situ reflux reaction process. The existence of CQDs results in a direct combination of electrons and holes from the CB of TiO2 and VB of Cd0.5Zn0.5S, and retains the active electron and holes in this system. Besides, it also benefits from the excellent optical absorption and prolonging electron lifetime, the ternary system shows excellent activity during photocatalytic water splitting with a high H2 production rate of 38.74 mmol·h − 1·m − 2, which is 3.4 and 1.5 times higher than that of pure TiO2 and CZS/TiO2 type II heterojunction without CQDs. In addition, CQDs bridged semiconductors as all solid-state Z-scheme heterojunction exhibit good stability and reusability.