Facet-Dependent Photocatalytic Behaviors of ZnS-Decorated Cu₂O Polyhedra Arising from Tunable Interfacial Band Alignment

Abstract

ZnS particles were grown over Cu2O cubes, octahedra, and rhombic dodecahedra for examination of their facet-dependent photocatalytic behaviors. After ZnS growth, Cu2O cubes stay photocatalytically inactive. ZnS-decorated Cu2O octahedra show enhanced photocatalytic activity, resulting from better charge carrier separation upon photoexcitation. Surprisingly, Cu2O rhombic dodecahedra give greatly suppressed photocatalytic activity after ZnS deposition. Electron paramagnetic resonance spectra agree with these experimental observations. Time-resolved photoluminescence profiles provide charge-transfer insights. The decrease in the photocatalytic activity is attributed to an unfavorable band alignment caused by significant band bending within the Cu2O­(110)/ZnS­(200) plane interface. A modified Cu2O–ZnS band diagram is presented. Density functional theory calculations generating plane-specific band energy diagrams of Cu2O and ZnS match well with the experimental results, showing that charge transfer across the Cu2O­(110)/ZnS­(200) plane interface would not happen. This example further illustrates that the actual photocatalysis outcome for semiconductor heterojunctions cannot be assumed because interfacial charge transfer is strongly facet-dependent.

Mechanistic Insights into Photodegradation of Organic Dyes Using Heterostructure Photocatalysts

“…These observations indicate that the interfacial charge transfer kinetics of the photocatalysts play an important role for the photodegradation of dye molecules. Moreover, the composition and facet effects of heterostructure systems such as TiO 2 -Au@Cu 7 S 4 [85] and ZnS-Cu 2 O [86] also influence the photodegradation efficiency. [81].…”

Step-scheme porous g-C3N4/Zn0.2Cd0.8S-DETA composites for efficient and stable photocatalytic H2 production

“…In recent years, solid solutions have been extensively studied because of their excellent performances under visible light irradiation [38][39][40]. Zinc sulfide (ZnS) exhibits good photocatalytic activity and stability owing to its high conduction band energy position [41,42]. However, ZnS has a wide band gap (of about 3.5 eV) and can only be excited with ultraviolet light.…”

Density Functional Theory Calculations Revealing Metal‐like Band Structures and Work Function Variation for Ultrathin Gallium Arsenide (111) Surface Layers

“…All these semiconductors, including Ag 3 PO 4 crystals, display current‐rectifying effects when electrical contacts are made on two different crystal faces . Furthermore, Cu 2 O, Ag 2 O, and Ag 3 PO 4 crystals, as well as Cu 2 O‐based semiconductor heterojunctions, also present facet‐dependent or interfacial plane‐related photocatalytic properties from high photocatalytic efficiency to total deactivation . The emergence of these semiconductor facet effects should originate from the presence of an ultrathin surface layer with dissimilar band structures for different crystal planes as revealed through DFT calculations, such that charge carriers encounter different barrier heights across a particular crystal surface .…”

“…Furthermore, Cu 2 O, Ag 2 O, and Ag 3 PO 4 crystals, as well as Cu 2 O‐based semiconductor heterojunctions, also present facet‐dependent or interfacial plane‐related photocatalytic properties from high photocatalytic efficiency to total deactivation . The emergence of these semiconductor facet effects should originate from the presence of an ultrathin surface layer with dissimilar band structures for different crystal planes as revealed through DFT calculations, such that charge carriers encounter different barrier heights across a particular crystal surface . This ultrathin surface layer should also be responsible for the observation of optical facet effects demonstrated in polyhedral Cu 2 O and Ag 3 PO 4 nanocrystals, suggesting light absorption of semiconductor crystals actually has bulk and surface components .…”