This work shows a novel artificial donor-catalyst-acceptor triad photosystem based on a mononuclear C5 H5 -RuH complex oxo-bridged TiO2 hybrid for efficient CO2 photoreduction. An impressive quantum efficiency of 0.56 % for CH4 under visible-light irradiation was achieved over the triad photocatalyst, in which TiO2 and C5 H5 -RuH serve as the electron collector and CO2 -reduction site and the photon-harvester and water-oxidation site, respectively. The fast electron injection from the excited Ru(2+) cation to TiO2 in ca. 0.5 ps and the slow backward charge recombination in half-life of ca. 9.8 μs result in a long-lived D(+) -C-A(-) charge-separated state responsible for the solar-fuel production.

A series of novel surface Ru–H bipyridine complexes-grafted TiO2 nanohybrids were for the first time prepared by a combined procedure of surface organometallic chemistry with post-synthetic ligand exchange for photocatalytic conversion of CO2 to CH4 with H2 as electron and proton donors under visible light irradiation. The selectivity toward CH4 increased to 93.4% by the ligand exchange of 4,4′-dimethyl-2,2′-bipyridine (4,4′-bpy) with the surface cyclopentadienyl (Cp)–RuH complex and the CO2 methanation activity was enhanced by 4.4-fold. An impressive rate of 241.2 μL·g–1·h–1 for CH4 production was achieved over the optimal photocatalyst. The femtosecond transient IR absorption results demonstrated that the hot electrons were fast injected in 0.9 ps from the photoexcited surface 4,4′-bpy–RuH complex into the conduction band of TiO2 nanoparticles to form a charge-separated state with an average lifetime of ca. 50.0 ns responsible for the CO2 methanation. The spectral characterizations indicated clearly that the formation of CO2 •– radicals by single electron reduction of CO2 molecules adsorbed on surface oxygen vacancies of TiO2 nanoparticles was the most critical step for the methanation. Such radical intermediates were inserted into the explored Ru–H bond to generate Ru–OOCH species and finally CH4 and H2O in the presence of H2.

Metal-decorated oxide semiconductors are overwhelming photocatalysts for nonoxidative coupling of methane (NOCM). However, the overall NOCM mechanism remains an unopened black box, which hinders the design of high-performance catalysts. Herein, we systematically studied a series of noble metal (Ag, Au, Pt, Pd, Cu, and Ni)-decorated oxides (NaTaO3, CaTiO3, LiNbO3, and TiO2) for NOCM. We proposed that the active sites for H abstraction and C–C coupling of CH4 are spatially separated. Specifically, NaTaO3 only completes the initial H abstraction of CH4 activation, while metal nanoparticles are responsible for the final C–C coupling. Noble metals dominate NOCM by significantly decreasing the energy barrier of CH4 dissociation and promoting C–C coupling. Among various metals, Ag is preferential for the weak adsorption of ·CH3 intermediates and subsequent metal-induced C–C coupling. This contributes to Ag/NaTaO3 the highest C2H6 yield of 194 μmol g–1 h–1 and stoichiometric H2 with 11.2% quantum efficiency. This work provides a molecular-level insight into the CH4 coupling mechanism on metal-decorated photocatalysts.

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The keto‐switched photocatalysis of covalent organic frameworks (COFs) for efficient H2 evolution was reported for the first time by engineering, at a molecular level, the local structure and component of the skeletal building blocks. A series of imine‐linked BT‐COFs were synthesized by the Schiff‐base reaction of 1, 3, 5‐benzenetrialdehyde with diamines to demonstrate the structural reconstruction of enol to keto configurations by alkaline catalysis. The keto groups of the skeletal building blocks served as active injectors, where hot π‐electrons were provided to Pt nanoparticles (NPs) across a polyvinylpyrrolidone (PVP) insulting layer. The characterization results, together with density functional theory calculations, indicated clearly that the formation of keto‐injectors not only made the conduction band level more negative, but also led to an inhomogeneous charge distribution in the donor‐acceptor molecular building blocks to form a strong intramolecular built‐in electric field. As a result, visible‐light photocatalysis of TP‐COFs‐1 with one keto group in the skeletal building blocks was successfully enabled and achieved an impressive H2 evolution rate as high as 0.96 mmol g−1 h−1. Also, the photocatalytic H2 evolution rates of the reconstructed BT‐COFs‐2 and ‐3 with two and three keto‐injectors were significantly enhanced by alkaline post‐treatment.