Amorphous Co3O4 quantum dots hybridizing with 3D hexagonal CdS single crystals to construct a 0D/3D p–n heterojunction for a highly efficient photocatalytic H2 evolution

Abstract

Herein, a novel amorphous monodisperse Co₃O₄ quantum dots/3D hexagonal CdS single crystals (0D/3D Co₃O₄ QDs/CdS) p–n heterojunction was constructed by a simple hydrothermal and electrostatic self-assembly method. The amorphous monodispersed Co₃O₄ QDs (≈4.5 nm) are uniformly and tightly attached to the surface of the hexagonal CdS single crystals. The sample, 0.5% CQDs/CdS exhibits outstanding hydrogen evolution activity of 17.5 mmol h⁻¹ g⁻¹ with a turnover number (TON) of 4214, up to 10.3 times higher than that of pure CdS. The enhanced photocatalytic activity can be attributed to the synergistic effect of the p–n heterostructure and the quantum confinement effect of Co₃O₄ QDs, which significantly promoted the separation efficiency of photo-generated electrons and holes. Additionally, the sulfur vacancy also can act as electron trappers to improve carrier separation and electron transfer. The photoelectrochemical and time-resolved fluorescence (TRPL) results further certify the effective spatial charge separation. This work gives an insight into the design of the 0D/3D Co₃O₄ QDs/CdS p–n heterostructure for a highly efficient photocatalysis.