Photocatalytic Activity Suppression of CdS Nanoparticle-Decorated Cu2O Octahedra and Rhombic Dodecahedra

Wurtzite CdS nanoparticles have been lightly deposited on Cu2O cubes, octahedra, and rhombic dodecahedra to examine facet effects on the interfacial charge transfer in a photocatalytic reaction. Instead of an expected photocatalytic activity enhancement on the basis of a favorable band alignment at the heterojunction, CdS-decorated Cu2O octahedra and rhombic dodecahedra show drastically reduced photocatalytic activities. Further increasing the CdS deposition amount leads to complete suppression of photocatalytic activity. Cu2O cubes remain inactive even after CdS deposition. Transmission electron microscopy analysis reveals epitaxial growth of the (101) planes of CdS on the (110) planes of a Cu2O rhombic dodecahedron, whereas the (110) planes of CdS align parallel to the (111) planes of a Cu2O octahedron. Because facet-dependent photocatalytic activity can be understood from different degrees of band bending at the crystal surfaces, significantly upward bending for the CdS-contacting planes can explain the observed photocatalytic inactivity. This work demonstrates that strong facet effects tuning the band energies of both semiconductors at the heterojunctions make the predictions of an enhanced photocatalytic activity, simply through bulk band energy alignment analysis, highly unreliable.