Inactive Cu₂O Cubes Become Highly Photocatalytically Active with Ag₂S Deposition

Abstract

Previously, Cu2O cubes have been shown to remain photocatalytically inert toward methyl orange degradation even after surface decoration with ZnO, ZnS, CdS, and Ag3PO4 nanostructures. Surprisingly, when Ag2S nanoparticles are lightly deposited on Cu2O cubes as seen through scanning electron microscopy (SEM) images, the heterostructures become highly photocatalytically active. X-ray diffraction (XRD) patterns show mainly Cu2O diffraction peaks due to lightly deposited Ag2S, but Ag2S peaks can emerge with increased Ag2S deposition. X-ray photoelectron spectroscopy (XPS) analysis also supports Ag2S formation on Cu2O crystals. The Ag2S-deposited Cu2O octahedra and rhombic dodecahedra show the expected activity enhancement. Electron paramagnetic resonance (EPR) measurements, as well as electron, hole, and radical scavenger tests, all confirmed the emergence of photocatalytic activity from the Ag2S–Cu2O cubes. Photoluminescence lifetimes are shortened after Ag2S deposition. Electrochemical impedance measurements revealed a large decrease in charge transfer resistance for Cu2O cubes after the Ag2S deposition. Unexpectedly, the separately synthesized Ag2S particles are also photocatalytically inactive. No specific lattice planes of Ag2S are formed directly over the {100} face of Cu2O. Diffuse reflectance and ultraviolet photoelectron spectral data were used to construct band diagrams of different Cu2O crystals and Ag2S nanoparticles. A Z-scheme charge transfer mechanism may be involved at the heterojunction interface to promote charge carrier separation. However, to explain the sudden appearance of photocatalytic activity from the Ag2S-deposited Cu2O cubes, a large change in the {100} surface band bending after Ag2S deposition should be used. This work illustrates that an unusual photocatalytic outcome is possible to semiconductor heterojunctions, where two photocatalytically inert components can become highly active when joined together.

Copper Oxide-Based Photocatalysts and Photocathodes: Fundamentals and Recent Advances

“…The cocatalysts can be classified into two roles: the cocatalyst trapping electrons for reduction half reactions (e.g., reduction of H 2 O or CO 2 ) and the cocatalyst trapping holes for oxidation half reactions (e.g., oxidation of H 2 O or organic species). In general, noble metals (e.g., Pt, Pd, Rh and Au, Ru) [ 39 , 48 , 236 , 237 , 238 , 239 , 240 ], non-noble transition metals (e.g., Cu, Zn, Al, Co and Ni) [ 184 , 241 , 242 , 243 , 244 , 245 ], metal oxides (RuO 2 , NiO x, Bi 2 O 3 ) [ 80 , 190 , 246 , 247 , 248 ] and metal sulfides (e.g., ZnS, MoS 2 , NiS, Ag 2 S, and WS 2 ) [ 187 , 245 , 249 , 250 , 251 ] were reported as cocatalysts deposited on CuO and/or Cu 2 O.…”

Current Rectification and Photo-Responsive Current Achieved through Interfacial Facet Control of Cu2O–Si Wafer Heterojunctions

“…Multiple interfacial combinations are possible. In all these heterostructure cases, Cu 2 O cubes remain photocatalytically inert, but Ag 2 S-decorated Cu 2 O cubes show surprisingly good photocatalytic activity, illustrating the unpredictable nature of semiconductor heterojunctions …”

“…In all these heterostructure cases, Cu 2 O cubes remain photocatalytically inert, but Ag 2 S-decorated Cu 2 O cubes show surprisingly good photocatalytic activity, illustrating the unpredictable nature of semiconductor heterojunctions. 28 Since one knows diverse photocatalytic outcomes are possible for semiconductor heterojunctions, it is natural to think electrical properties of semiconductor heterojunctions with facet control can produce the same current-rectifying effect. The placement of a Cu 2 O cube, octahedron, and rhombic dodecahedron on Si {100}, {111}, and {110} wafers gives 9 combinations to investigate.…”

Photocatalytic activity enhancement of Cu2O cubes functionalized with 2-ethynyl-6-methoxynaphthalene through band structure modulation

“…Unexpectedly, Ag 2 S-deposited Cu 2 O cubes were found to be highly photocatalytically active possibly because the interfacial band bending is favorable, illustrating the unpredictable nature of photocatalytic activity in semiconductor heterostructures with well-defined planes for at least one material of the heterojunction. 24…”