Ab Initio Simulations of Copper Oxide Nanowires and Clusters on TiO₂ (101) Anatase Surface

Abstract

Copper oxides deposited at titania surfaces have a beneficial effect on the photocatalytic activity of TiO2, but their role is not fully understood. In this work, possible nanostructures of copper oxide on TiO2 (101) have been investigated by simulations based on density functional theory. Various stoichiometries, from Cu2O to CuO, and morphologies, from clusters to nanowires, have been considered. Nanowire structures were consistently more stable than isolated clusters. In these structures, a Cu2O stoichiometry was found to be thermodynamically more stable than CuO at room conditions, in contrast to what happens in bulk copper. Occupied Cu 3d and O 2p states extend well into the band gap of titania, whereas the nature of the lowest-lying empty states depend on the stoichiometry: for Cu2O they consist mostly of Ti 3d orbitals, while in CuO unoccupied Cu 3d orbital ∼0.8 eV above the Fermi level are present. Thus, both oxides reduce the band gap of the system with respect to pure titania, but only Cu2O should be effective in separating photogenerated electrons and holes. These results provide insight into the role of copper oxides in the photocatalytic process.

Simultaneous Control over Lattice Doping and Nanocluster Modification of a Hybrid CuOx/TiO2 Photocatalyst during Flame Synthesis for Enhancing Hydrogen Evolution

“…The role of surface deposited CuO x clusters in the photocatalytic H 2 production activities is also two‐sided. As reported, although both Cu 2 O and CuO nanocluster can narrow the band gap with respect to the pure TiO 2 , only Cu 2 O could enhance the electron‐hole separation through staggered band structure alignment, thus promoting photocatalytic reaction. For the deposition of CuO nanoclusters on the surface of TiO 2 , photo‐generated electrons and holes will transfer from the conduction band (CB) and valence band (VB) of TiO 2 to that of CuO.…”

“…Compared to FSP‐TiO 2 , the absorption edges of the samples exhibit a notable red shift, indicating that doping of Cu species will enhance visible‐light absorption of the catalysts. The estimated width of band gaps decrease with the increase of Cu content, which may due to the generation of defects and the formation of CuO x nanoclusters . The increased content of rutile may also contribute to the band‐gap narrowing, as the band gap of rutile‐TiO 2 is narrow than that of anatase‐TiO 2 .…”

“…The estimated width of band gaps decrease with the increase of Cu content, which may due to the generation of defects [38,39] and the formation of CuO x nanoclusters. [15,40] The increased content www.advancedsciencenews.com www.solar-rrl.com of rutile may also contribute to the band-gap narrowing, as the band gap of rutile-TiO 2 is narrow than that of anatase-TiO 2 . The estimated band gap of CuTi-20 is %0.2 eV narrower than that of CuTi-0.5.…”

“…Among various elements doped so far into TiO 2 , Cu has been considered to be important owing to the narrow band‐gap energies of its oxides (CuO possesses 1.4 eV and Cu 2 O possesses 2.2 eV) and their high light absorption coefficients . More than that, surface cluster modification through copper has been proven to be an effient tool for promoting charge separtion …”

“…[9][10][11][12][13] More than that, surface cluster modification through copper has been proven to be an effient tool for promoting charge separtion. [12,14,15] For all applications, synthetic techniques, which provide precise control over nanocrystal grain composition and size, are crucial in that they permit engineering of photocatalysis.…”