Facet-Specific Photocatalytic Activity Enhancement of Cu₂O Polyhedra Functionalized with 4-Ethynylanaline Resulting from Band Structure Tuning

Abstract

Cu 2 O rhombic dodecahedra, octahedra, and cubes were densely modified with conjugated 4-ethynylaniline (4-EA) for facet-dependent photocatalytic activity examination. Infrared spectroscopy affirms bonding of the acetylenic group of 4-EA onto the surface copper atoms. The photocatalytically inactive Cu 2 O cubes showed surprisingly high activity toward methyl orange photodegradation after 4-EA modification, while the already active Cu 2 O rhombic dodecahedra and octahedra exhibited a photocatalytic activity enhancement. Electron, hole, and radical scavenger experiments prove that the photocatalytic charge transport processes have occurred in the functionalized Cu 2 O cubes. Electrochemical impedance spectroscopy also indicates reduced charge transfer resistance of the functionalized Cu 2 O crystals. A band diagram constructed from UV−vis spectral and Mott−Schottky measurements reveals significant band energy shifts in all Cu 2 O samples after decorating with 4-EA. From density functional theory (DFT) calculations, a new band has emerged slightly above the valence band maximum within the band gap of Cu 2 O, which has been found to originate from 4-EA through banddecomposed charge density analysis. The increased charge density localized on the 4-EA molecule and the smallest electron transition energy to reach the 4-EA-generated band are factors making {100}-bound Cu 2 O cubes photocatalytically active. Proper molecular decoration represents a powerful approach to improving the photocatalytic efficiency of semiconductors.

Defective cuprous oxide as a selective surface‐enhanced Raman scattering sensor of dye adulteration in Chinese herbal medicines

“…where C is the space-charge capacitance of the semiconductor, e is the electron charge (1.62 Â 10 À19 C), ε is the permittivity of the dielectric constant (7.6 for Cu 2 O), ε 0 is the permittivity of the vacuum (8.85 Â 10 À14 F cm À1 ), N A is the carrier density, E is the applied potential, V fb is the flat band potential, k is Boltzmann's constant, and T is the absolute temperature. [25] Interestingly, a negative slope can be observed in Figure 2b, suggestive of an ntype nature of the obtained Cu 2 O nanocubes. Although still a matter of debate, the n-type conductivity displayed by Cu 2 O thin films has long been observed, [26][27][28][29][30] especially for substoichiometric Cu 2 O samples with oxygen vacancies.…”

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

“…36 2E-6MN shows a peak at = 3257 cm −1 , corresponding to the stretching vibrations of the acetylenic hydrogen (CC–H). 33 The peaks around 3000 cm −1 should arise from the C–H bond stretching modes of naphthalene and the methoxy group. 37 Moreover, the peaks due to the CC stretching vibrations of the aromatic ring show up at = 1625 and 1598 cm −1 .…”

“…32 Recent surface functionalization of Cu 2 O crystals with conjugated 4-ethynylaniline (4-EA) showed an unexpected excellent photocatalytic activity for Cu 2 O cubes, while rhombic dodecahedra gave a notably improved activity and octahedra presented a moderate activity enhancement. 33 DFT calculations have revealed a 4-EA-derived band within the band gap of Cu 2 O. The appearance of this band with energies close to the valence band of the {100}-terminated Cu 2 O, and the observed electron density distribution over the anchored molecule, are believed to make the inert cubes highly active.…”

Well-defined Cu2O photocatalysts for solar fuels and chemicals

“…Most surprisingly, a recent study demonstrated that a dense decoration of 4-ethynylaniline around the cubic Cu 2 O nanocrystals altered its band gap and modied the charge carrier transport mechanism through the {100} facet, which led to an enhanced activity. 132 Therefore, the surface-bound ligands can have a profound impact on the photocatalytic activity of a semiconductor nanocrystal. The photocatalytic dye degradation efficiency of pristine Cu 2 O nanocrystals has further been improved by forming heterostructures.…”