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The photocatalytic conversion of CO2 to fuels by light is of research interest owing to its relevance to environment and energy concerns. In this work, a hybrid H-TiO2–rGO–Re(bpy)(CO)3Cl composite consisting of a rhenium 2,2′-bipyridine compound, Re(bpy)(CO)3Cl, which was covalently grafted on reduced graphene oxide (rGO) and hydrogenated TiO2 (H-TiO2) was prepared. H-TiO2–rGO–Re(bpy)(CO)3Cl demonstrated high efficiency for visible light photo-conversion of CO2 into CO in triethanolamine/N,N-dimethylformamide (V:V = 1:9) solution with total turnover numbers larger than 580. In addition, the composite showed high stability with no leveling-off tendency after four catalytic experimental runs. The experimental results indicate that the suitable assembly of the Re(bpy)(CO)3Cl, rGO, and H-TiO2 components in the H-TiO2–rGO–Re(bpy)(CO)3Cl composite is necessary for the observed high performance of the catalyst for CO2 reduction under visible light irradiation.

N–doped TiO2 effectively extends the light response range of TiO2 photocatalysts from the ultraviolet to the visible region; a p–n heterojunction would favor the separation of photogenerated electron–hole pairs, leading to high quantum efficiency, and consequently, enhanced photocatalysis. A Cu2O/N–TiO2 hybrid catalyst with p-n heterojunctions was newly prepared using a solvothermal and chemical reduction method. The hierarchical structure and valence state of copper of the Cu2O/N–TiO2 catalyst have been confirmed using X-ray diffraction, high resolution transmission electron microscopy, and X-ray photoelectron spectroscopy. The hybrid Cu2O/N–TiO2 catalyst demonstrated good photostability and excellent photocatalytic activity toward H2 production, with a rate of 11 μmol g−1 h−1 under visible light irradiation (>400 nm) of a methanol aqueous solution. This offers an inexpensive and facile approach for potential efficient solar photon-driven H2 production.

Metallic doping effectively extends the light response range of TiO2 photocatalysts from the ultraviolet (UV) to the visible region. We prepared Ce-doped TiO2 nanotubes (Ce-TiO2 NTs) using a sol–gel process followed by a hydrothermal treatment. The Ce-TiO2 NTs were characterized by X-ray diffraction, transmission electron microscopy, Brunauer–Emmett–Teller surface area, X-ray photoelectron spectroscopy, UV–Vis diffuse reflectance spectroscopy (UV–Vis DRS), and photoluminescence (PL) spectroscopy. Given that the optical absorption was extended to wavelengths of 600 nm, the Ce-TiO2 NTs demonstrated excellent photocatalytic activity for degrading methylene blue under visible light irradiation. Ce-TiO2 NTs with various amounts of Ce doping (0.06–0.40 g of cerium nitrate hexahydrate added during preparation) were tested, and the 0.12Ce-TiO2 NTs showed the highest photocatalytic activity, 7 times higher than that of P25. For their efficient photodegrading of dyes under visible light, these Ce-TiO2 NTs may be useful for waste water treatment.