Synergistic effect of noble metal Pt and Zn0.25Cd0.75S QDs on ZnO: Broad spectral response and its outstanding photocatalytic performance

Abstract

In this paper, based on the modification of semiconductor ZnO by solid solution heterojunction and noble metal photoreduction, Pt/Zn_0.25Cd_0.75S QDs/ZnO composite with a broad spectral response was synthesized, and crystal structure, morphology, optical properties, specific surface area and electrochemical properties of composites were investigated and discussed. The prepared composite has a skeleton structure, in which the solid solution Zn_0.25Cd_0.75S mainly exists in the form of quantum dots (QDs), and Pt is mostly simple nanoparticles. After ZnO was modified by solid solution Zn_xCd_1−xS QDs and precious metal Pt with surface plasmon resonance effect, the composite has strong light absorption ability in the visible region. Compared with the ZnO monomer, 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 exhibit 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 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 the composite Pt/Zn_0.25Cd_0.75S QDs/ZnO is more inclined to be the effect of "Z-type" heterostructure.