Synergistic effect of noble metal Pt and Zn_0.25Cd_0.75S QDs on ZnO: broad spectral response and its outstanding photocatalytic performance

Constructing heterostructures can accelerate the separation of electrons and holes, prolong the lifetime of photogenerated charge carriers, and have an important impact on improving photocatalytic activity. The Zn_0.25Cd_0.75S QDs/ZnO heterostructure was constructed by the hydrothermal method, which was further modified by Pt through the photo-deposition process, and then Pt/Zn_0.25Cd_0.75S QDs/ZnO composites with broad spectral response were finally synthesized. The composites are mainly composed of nanoparticle agglomerates, in which the solid solution Zn_0.25Cd_0.75S mainly exists in the form of quantum dots (QDs), while Pt with surface plasmon resonance (SPR) effect exists in elemental form. Compared with ZnO, the specific surface area of the nanoparticle framework has a significant enhancement, thus increasing the active sites for the photocatalytic reaction. In addition, the results of the transient photocurrent response tests and the electrochemical impedance tests show that Pt/Zn_0.25Cd_0.75S QDs/ZnO composite has a better carrier separation efficiency with the fastest electron transfer rate and the lowest charge transfer resistance compared with other reference systems. Furthermore, the composite exhibits excellent photocatalytic performance in the multi-mode photocatalytic degradation of dye molecules. The results of photocatalytic water splitting into hydrogen show that the hydrogen production capacity of the Pt/Zn_0.25Cd_0.75S QDs/ZnO composite is 33.67 mmol·g⁻¹ in 8 h, which is 207 times higher than that of commercially available P25. Combined with the results of the capture experiments, it is finally determined that the possible photocatalytic mechanism of Pt/Zn_0.25Cd_0.75S QDs/ZnO is more inclined to be the effect of the “Z-type” energy band structure theory based on Pt as the electronic transducer between ZnO and Zn_0.25Cd_0.75S.