From single ZnO multipods to heterostructured ZnO/ZnS, ZnO/ZnSe, ZnO/Bi2S3 and ZnO/Cu2S multipods: controlled synthesis and tunable optical and photoelectrochemical properties

Abstract

This manuscript describes the selective modification of ZnO multipods with a series of wide bandgap and narrow bandgap semiconductors (ZnS, ZnSe, Bi₂S₃, and Cu₂S). ZnO multipods are firstly synthesized via the aqueous phase reaction of Zn²⁺ ions with KOH at a temperature lower than 70 °C, which is simple, facile and free of organic capping agents. Through the reaction of the chalcogen source (Na₂S₂O₃ or Na₂SeSO₃) with the multipods supported by zinc or copper sheet, heterostructured ZnO/ZnS, ZnO/ZnSe, ZnO/Bi₂S₃ and ZnO/Cu₂S multipods are formed. The particles of ZnS and ZnSe are selectively deposited on the tips of the multipods but Cu₂S and Bi₂S₃ are randomly distributed on the entire surfaces of the multipods. The difference among the deposition sites of ZnS, ZnSe, Cu₂S, and Bi₂S₃ is related to the different structural affinity of these semiconductors to ZnO multipods. The heterostructures have integrated the optical absorption properties of ZnO multipods and the deposited semiconductors, and as a result, the optical absorption range of ZnO multipods is expanded (335∼1000 nm). The photoelectrochemical properties of the heterostructures are also different from that of bare ZnO multipods. The photocurrent densities yielded by bare ZnO multipods, heterostructured ZnO/ZnS, ZnO/ZnSe, and ZnO/Bi₂S₃ multipods are 0.08 mA cm⁻², 0.10 mA cm⁻², 0.30 mA cm⁻², and 0.03 mA cm⁻², respectively. As for ZnO/Cu₂S multipods, the photocurrent is unexpectedly smaller than the dark current.