3R-delafossite CuGaO2 sample with high crystallinity and single phase was prepared by simple low-temperature hydrothermal method. The fundamental physicochemical properties of 3R-delafossite CuGaO2 were systematically studied by density functional theory calculations and experimental characterization. Through a series of characterization, analysis, (photo)electrochemical and photocatalytic activity testing, the as-prepared CuGaO2 samples exhibit the potential for hydrogen production and high photocatalytic degradation for tetracycline hydrochloride (TCH). Furthermore, CuGaO2 photoelectrode exhibits long-term stability and large photocurrent density. These observations suggest that 3R-delafossite CuGaO2 is a potential promising photocatalyst driven by visible-light. Finally, possible breakthrough directions of 3R-delafossite CuGaO2 photocatalyst are discussed.

Internal polarized electric field is found to be an effective and available strategy to separate photogenerated electron−hole pairs. By this method, the efficiency of photocatalytic reactions can be obviously enhanced. Here, the layered compound of BiOIO 3 with spontaneous polarization was synthesized by a simple hydrothermal method. Taking another bismuth compound BiOI as a counterpart, which has a similar layered structure, the spontaneous polarization effects of BiOIO 3 were analyzed and confirmed. The photocatalytic activity of BiOIO 3 and BiOI were evaluated by the degradation of methyl orange. Methyl orange was almost completely photocatalytically decomposed by BiOIO 3 and BiOI in 40 and 90 min, respectively. The separation and transfer behaviors of photogenerated electron−hole pairs were investigated by a series of photoelectrochemical characterizations. It is further proved the separation and transmission efficiency of BiOIO 3 are higher than those of BiOI. According to the results of density of theory calculations, the internal polarized electric field in BiOIO 3 is ascribed to the spatial asymmetry of the IO 3 group, which is estimated to ∼1.5 × 10 10 V/m. Under the action of this internal polarized electric field, the photogenerated electrons and holes would transfer along opposite directions, i.e., photogenerated electrons and holes respectively gather at the Bi/I side and O side. Additionally, superoxide radicals (•O 2 − ) and holes (h + ) are produced during the degradation process, which are responsible for the high visible-light photocatalytic activity. Finally, the cyclic degradation test proves that its photocatalytic performance has long-term stability. Therefore, BiOIO 3 polar material can be used as one of the alternative materials for efficient photocatalytic reaction.

Localized surface plasmon resonance (LSPR) plays a significant role in the fields of photocatalysis and solar cells. It can not only broaden the spectral response range of materials, but also improve the separation probability of photo-generated electron-hole pairs through local field enhancement or hot electron injection. In this article, the LSPR effects of Au/TiO2 composite photocatalyst, with different sizes and shapes, have been simulated by the finite difference time domain (FDTD) method. The variation tendency of the resonance-absorption peaks and the intensity of enhanced local enhanced electric field were systematically compared and emphasized. When the location of Au nanosphere is gradually immersed into the TiO2 substrate, the local enhanced electric field of the boundary is gradually enhanced. When Au nanoshperes are covered by TiO2 at 100 nm depths, the local enhanced electric field intensities reach the maximum value. However, when Au nanorods are loaded on the surface of the TiO2 substrate, the intensity of the corresponding enhanced local enhanced electric field is the maximum. Au nanospheres produce two strong absorption peaks in the visible light region, which are induced by the LSPR effect and interband transitions between Au nanoparticles and the TiO2 substrate. For the LSPR resonance-absorption peaks, the corresponding position is red-shifted by about 100 nm, as the location of Au nanospheres are gradually immersed into the TiO2 substrate. On the other hand, the size change of the Au nanorods do not lead to a similar variation of the LSPR resonance-absorption peaks, except to change the length-diameter ratio. Meanwhile, the LSPR effects are obviously interfered with by the interband transitions between the Au nanorods and TiO2 substrate. At the end of this article, three photo-generated carrier separation mechanisms are proposed. Among them, the existence of direct electron transfer between Au nanoparticles and the TiO2 substrate leads to the enhanced local enhanced electric field at the boundaries, which is favorable for the improvement of photocatalytic performance of TiO2. These findings could explain the underlying mechanism of some experimental observations in published experimental works, and helpful to design highly efficient composite photocatalysts that contain noble metal co-catalyst nanoparticles.

The presence of Cu₂O covering in Cu/TiO₂ composite can move LSPR peak out of inter-band transition range, create more interfaces, induce Fano resonance effect, facilitate hot electron injection, and may constitute a Z-Scheme of Cu₂O/Cu/TiO₂.