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

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.