Site-selective doping induced synergistic effect of midgap states and aspect ratio-related charge transfer in Ag2S-ZnS heterostructure toward H2 photoproduction

Abstract

Ag2S-ZnS (AZ) heterostructures with tunable aspect ratio (AR) and band structure were successfully synthesized by site-selective doping of metal ions. TEM and XPS results showed that by doping Cu, Mn and Cd ions in AZ heterostructures (Cu: AZ, Mn: AZ and Cd: AZ), respectively, the morphology of AZ heterostructures changed from tadpole-shape (Cu: AZ with AR of 1.2) to matchstick-shape (Cd: AZ with AR of 3.9) due to the selective doping of Cu ions in Ag2S head and Cd ions in ZnS tail as well as the doping of Mn ions both in Ag2S head and ZnS tail (Mn: AZ with AR of 2.7). All the UV-Vis spectra of doped AZ showed Urbach tail absorption, suggesting the existence of midgap-states created by metal ion dopants, which was confirmed by PL results. Cd: AZ with the largest AR values and Cd-doping induced midgap states showed the highest photocatalytic H2-production rate of 1443.55 μmol h−1 g−1. The catalytic activity of the Cd: AZ can be ascribed to the synergistic effect of midgap states and aspect ratio-dependent charge transfer, which all originate from the site-selective doping of metal ions. This investigation demonstrates a facile way to manipulate the charge carrier dynamics of semiconductor heterostructures by synergistic effects through simultaneously tuning and optimizing the electronic and morphological structures.