A series of Pd/TiO2 photocatalysts were synthesized by a simple glucose reduction method, and their photocatalysis properties were evaluated in an array of CO2 hydrogenations. The samples were characterized by XRD, SEM, TEM, EDX, EDX mapping, UV–vis DRS, Raman spectroscopy, PL spectroscopy, XPS, and N2 adsorption. In terms of product yields (in micromoles per gram of catalyst), a 1.0 wt % Pd/TiO2 catalyst (CH4, 355.62; CO, 46.35; C2H6, 39.69) was found to be superior to pristine TiO2 (CH4, 42.65; CO, 4.73; C2H6, 2.7) and other composites under UV irradiation for 3 h, possibly because of a synergistic effect between the palladium nanoparticles and the TiO2 support. The palladium nanoparticles on the surface of TiO2 substantially accelerated electron transfer and acted as active sites for the adsorption and activation of CO2 molecules, to promote CO2 hydrogenation. During the photocatalytic CO2 hydrogenation, dissociated hydrogen reacts with CO2 – activated on the Pd/TiO2 photocatalyst to form a new PdC surface species that is stable during the reaction and further transforms to generate methane. A detailed mechanism of photocatalytic CO2 hydrogenation is discussed to account for the performance of the Pd/TiO2 photocatalyst in the reaction.

A series of visible-light-active NH2-MIL-125/TiO2/CdS yolk–shell and hollow H-TiO2/CdS hybrid heterostructures were successfully synthesized via the hydrolysis of NH2-MIL-125 metal–organic framework (MOF) using thioacetamide (CH3CSNH2) and cadmium acetate (Cd (CH3COO)2·2H2O) by the post solvothermal method, after which the obtained heterostructures were applied to H2 photocatalytic production. Among the yolk–shell and hollow heterostructures, NH2-MIL-125/TiO2/CdS (30) and H-TiO2/CdS (30) exhibited the highest H2 production activity of 2997.482 and 1970. 813 μmol g–1 h–1, with the apparent quantum efficiency of 4.81% and 2.41% at 420 nm, respectively. These superior photocatalytic performances of the heterostructures could be due to the strong interaction of the component based on intimate contact, large surface area, and porous structures that assisted the mass transfer, thereby forming abundant reactive sites. Moreover, the introduction of CdS nanoparticles into the MOF derivatives enhanced the visible light absorption and improved the separation of electron–hole pairs via heterojunction with well-matched energy band gap. Furthermore, the H2 production rate of the yolk–shell and hollow heterostructures were 18 and 12 times greater than the bare CdS. A probable mechanism was also proposed for the heterostructures. This work could open up new directions for the development of MOF-derived photocatalysts.

Metal–organic framework (MOFs) based composites have received more research interest for photocatalytic applications during recent years.

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