Surface Functionalization of Cu₂O Polyhedra with Different Halide-Substituted Phenylacetylenes for Photocatalytic Activity Comparison

High Resolution Image Download MS PowerPoint Slide To further explore the substituent group effect on the charge-transfer ability of phenylacetylene molecules bonding to different Cu 2 O surfaces, particularly the halide-substituted phenylacetylenes, the photocatalytic activity properties of Cu 2 O cubes, octahedra, and rhombic dodecahedra functionalized with 1-ethynyl-4-fluorobenzene (4-FA), 1-chloro-4-ethynylbenzene (4-CA), and 1-bromo-4-ethynylbenzene (4-BA) were examined. The inert cubes showed the largest photocatalytic activity enhancement with 4-BA decoration, while 4-FA-modified cubes exhibited the smallest boost in activity. Notably, only slight photocatalytic performance improvements were observed for Cu 2 O octahedra and rhombic dodecahedra decorated with all of the halide-substituted phenylacetylenes. Electron paramagnetic resonance spectra of all of the modified cubes show intense signals from hydroxyl radical formation. The photogenerated holes are more important than the electrons to the photocatalytic activity of the functionalized cubes. Density functional theory (DFT) calculations indicate the formation of two narrow bands within the band gap for the Cu 2 O {100} surface modified with 4-XA (X = F, Cl, Br), just one 4-FA-derived band for the {110} surface, but no additional band for the 4-FA-bonded {111} surface. 4-XA functionalization on the {100} surface yields large decreases in the work function and ionization energy to facilitate electron removal from the Cu 2 O surface, yet 4-FA bonding on the {111} and {110} surfaces causes relatively smaller work function and ionization energy changes. Two electron-transfer mechanisms are proposed based on the DFT results. This work demonstrates that significant variations in photocatalytic activity enhancement exist, depending on the choice of the decorating molecules.