Cuprous oxide/hematite nanotubes (Cu2O/Fe2O3NTs) were prepared by a potentiostatic electrodeposited method, in which different structured Cu2O materials were modified onto Fe2O3 NTs surface. Among them, the material with double-layer Cu2O spheres (Cu2O/Fe2O3 NTs-30) showed excellent photoelectrocatalytic (PEC) properties with a suitable energy band gap (1.96 eV) and a smaller overpotential (0.18 V). Furthermore, Cu2O/Fe2O3 NTs-30 showed two types of synergisms in the PEC reduction of CO2: (i) between electrocatalysis and photocatalysis and (ii) between Cu2O and Fe2O3NTs. The faradaic efficiency and methanol yield reached 93% and 4.94 mmol L−1 cm−2 after 6 h, respectively.

The CdSeTe nanosheet (CdSeTe NS)/TiO2 nanotube (TiO2 NT) photoelectrocatalyst was obtained by the hydrothermal method by loading CdSeTe NSs onto TiO2 NTs which were prepared by an anodic oxidation method. The SEM and TEM results show that CdSeTe had a flaky structure with a large size of 300–400 nm and a small size of about 100 nm, which distributed on the TiO2 NT surface uniformly. The HRTEM and XRD characterization revealed that the CdSeTe NSs grew along the (100) and (002) orientations. Measured by UV-vis DRS and XPS, the energy band gap of the TiO2 NTs was narrowed from 3.20 eV to 1.48 eV by the introduction of the CdSeTe NSs, of which the conduction band and valence band are located at −0.46 eV and 1.02 eV, respectively. In the photoelectrocatalytic reduction CO2 process, the current density had a significant improvement after the decoration with the CdSeTe NSs, increasing from 0.31 mA cm−2 to 4.50 mA cm−2 at −0.8 V. Methanol was the predominant photoelectrocatalytic reduction product identified by chromatography, and it reached 1166.77 μmol L−1 after 5 h. In addition, the mechanism of the high efficiency photoelectrocatalytic reduction of CO2 to methanol was explained from the following aspects: energy band matching, high efficiency electron transmission and the stability of the catalyst.

In this paper, the CuO FCs/Fe2O3 NTs catalyst was obtained after Fe2O3 nanotubes (Fe2O3 NTs) were decorated with CuO flower clusters (CuO FCs) by the pulse electrochemical deposition method. The in situ vertically aligned Fe2O3 NTs were prepared on the ferrous substrate by a potentiostatic anodization method. The SEM result showed the volcano-like Fe2O3 NTs were arranged in order and the CuO FCs constituted of flaky CuO distributed on the Fe2O3 NTs surface uniformly. After CuO FCs were loaded on Fe2O3 NTs, the absorption of visible light was enhanced noticeably, and its band gap narrowed to 1.78 eV from 2.03 eV. The conduction band and valence band locating at −0.73 eV and 1.05 eV, respectively were further obtained. In the PEC reduction of CO2 process, methanol and ethanol were two major products identified by chromatography. Their contents reached 1.00 mmol L−1 cm−2 and 107.38 μmol L−1 cm−2 after 6 h, respectively. This high-efficiency catalyst with photoelectric dual catalytic interfaces has a great guidance and reference significance for CO2 reduction to liquid carbon fuels.

The opaque methylene blue (MB) dye wastewater hard to be degraded directly by photocatalytic (PC) oxidation was successfully decomposed by a new two-step process, in which electrocatalytic (EC) pre-oxidation was followed with photoelectric synergistic catalytic (PEC) oxidation. The SnO2/TiO2 NTs electrode was used as the anode, which simultaneously has superior EC and PC performance. In the pre-oxidation step, the opaque dye wastewater is decolorized by EC oxidation, and the wastewater becomes a light transmission system, which provides the necessary condition for PC oxidation. However, the individual EC oxidation will be of low current efficiency and high energy consumption for the decreasing of the pollutants concentration in wastewater. Thus, in second stage, the PC process was introduced, and the synergistic catalytic oxidation leads to high PEC oxidation efficiency, so that the complete mineralization of the MB dye wastewater was realized. The whole process is highly efficient and energy-saving, which opens a new avenue to degrade the high-chroma or opaque dye wastewater.Highlights► Electrocatalytic pre-oxidation method degradated methylene blue. ► Electrocatalytic pre-oxidation provides a light transmission system. ► The synergistic photoelectric catalysis is an efficient and energy-saving method.

The CdSeTe nanosheet (CdSeTe NS)/TiO2 nanotube (TiO2 NT) photoelectrocatalyst was obtained by the hydrothermal method by loading CdSeTe NSs onto TiO2 NTs which were prepared by an anodic oxidation method. The SEM and TEM results show that CdSeTe had a flaky structure with a large size of 300–400 nm and a small size of about 100 nm, which distributed on the TiO2 NT surface uniformly. The HRTEM and XRD characterization revealed that the CdSeTe NSs grew along the (100) and (002) orientations. Measured by UV-vis DRS and XPS, the energy band gap of the TiO2 NTs was narrowed from 3.20 eV to 1.48 eV by the introduction of the CdSeTe NSs, of which the conduction band and valence band are located at −0.46 eV and 1.02 eV, respectively. In the photoelectrocatalytic reduction CO2 process, the current density had a significant improvement after the decoration with the CdSeTe NSs, increasing from 0.31 mA cm−2 to 4.50 mA cm−2 at −0.8 V. Methanol was the predominant photoelectrocatalytic reduction product identified by chromatography, and it reached 1166.77 μmol L−1 after 5 h. In addition, the mechanism of the high efficiency photoelectrocatalytic reduction of CO2 to methanol was explained from the following aspects: energy band matching, high efficiency electron transmission and the stability of the catalyst.