Creation of Cu₂O@TiO₂ Composite Photocatalysts with p–n Heterojunctions Formed on Exposed Cu₂O Facets, Their Energy Band Alignment Study, and Their Enhanced Photocatalytic Activity under Illumination with Visible Light

Abstract

The creation of photocatalysts with controlled facets has become an important approach to enhance their activity. However, how the formation of heterojunctions on exposed facets could affect their photocatalytic performance ranking had not yet been investigated. In this study, Cu2O@TiO2 core-shell structures were created, and Cu2O/TiO2 p-n heterojunctions were formed on various exposed facets of Cu2O cubes, Cu2O cuboctahedra, and Cu2O octahedra, respectively. These Cu2O@TiO2 polyhedra demonstrated an enhanced photocatalytic degradation effect on Methylene Blue (MB) and 4-nitrophenol (4-NP) under visible light illumination, because of the enhanced charge carrier separation by the formation of Cu2O@TiO2 p-n heterojunctions. It was further found that their photocatalytic performance was also facet-dependent as pure Cu2O polyhedra, while the photocatalytic performance ranking of these Cu2O@TiO2 polyhedra was different with that of their corresponding Cu2O polyhedron cores. By the combination of optical property measurement and XPS analysis, the energy band alignments of these Cu2O@TiO2 polyhedra were determined, which demonstrated that Cu2O@TiO2 octahedra had the highest band offset for the separation of charge carriers. Thus, the charge-carrier-separation-driven force in Cu2O@TiO2 polyhedra was different from their corresponding Cu2O polyhedron cores, which resulted in their different surface photovoltage spectrum (SPS) responses and different photocatalytic performance rankings.

On the Origin of Enhanced Photocatalytic Activity of Copper-Modified Titania in the Oxidative Reaction Systems

“…Moreover, it was found that Cu 2 O@TiO 2 core-shell photocatalysts had different band offset values ( Figure 16C), demonstrating a clear facet-dependent activity. The photocatalytic performance of Cu 2 O@TiO 2 polyhedra was different with that of pure Cu 2 O polyhedra without TiO 2 shells, which could be attributed to the different driving forces for the charge carrier separation [105]. …”

“…Moreover, it was found that Cu2O@TiO2 core-shell photocatalysts had different band offset values ( Figure 16C), demonstrating a clear facet-dependent activity. The photocatalytic performance of Cu2O@TiO2 polyhedra was different with that of pure Cu2O polyhedra without TiO2 shells, which could be attributed to the different driving forces for the charge carrier separation [105]. It is well known that controlled morphology by application of exposed facets (faceted semiconductors) significantly enhances photocatalytic performance, due to excellent crystallinity and low content of defects, e.g., octahedral and decahedral anatase particles [103,104].…”

“…Therefore, it is not surprising that similar concept was applied for copper oxide-titania heterojunction systems. For example, Liu et al prepared Cu 2 O@TiO 2 photocatalysts using Cu 2 O with exposed facets [105]. First, Cu 2 O nanocrystals with different types of morphology: cubes, cuboctahedra and octahedra were synthesized, and then Cu 2 O@TiO 2 core-shell polyhedral nanostructures were prepared by hydrothermal reaction.…”

Hierarchical MoS2 intercalated clay hybrid nanosheets with enhanced catalytic activity

“…Nitroaromatic compounds are widely used as synthetic intermediates in the manufacture of pharmaceuticals, fungicides, pesticides, plasticizers, and dyes and are regarded as water pollutants owing to their presence in industrial effluents [43]. 4-Nitrophenol (4-NP)-one of the most important nitroaromaticshas been listed as a "priority pollutant" by the US Environmental Protection Agency because it is highly soluble, has good chemical stability, and is not easily removed by natural degradation.…”

Fabrication of TiO2/RGO/Cu2O heterostructure for photoelectrochemical hydrogen production

“…[9] Cuprous oxide (Cu 2 O) has been applied as an attractive photoelectrode material for Page 4 of 30 A c c e p t e d M a n u s c r i p t 4 hydrogen production, because Cu 2 O is a p-type semiconductor with narrow bandgap (1.9-2.2 eV) of which the conduction band and valence band are close to the reduction and oxidation potential for water splitting. [10][11][12][13] As previous reports, [14,15] wide bandgap semiconductor (such as TiO 2 and ZnO) modified with Cu 2 O nanoparticles can significantly expand their absorption spectra range. However, the low interfacial area between different semiconductors directly influenced the separation efficiency of electrons and holes, so interfacial optimization of heterogeneous becomes a feasible way to further improving photoelectrochemical conversion efficiency.…”