A hexanuclear cobalt metal-organic framework for efficient CO2 reduction under visible light

Increasing global challenges including climate warming and energy shortage have stimulated worldwide explorations for efficient materials for applications in the capture of CO2 and its conversion to chemicals. In this study, a novel pillared-layer porous metal-organic framework (Co-6-MOF) with high nuclearity Co-II clusters has been synthesized. This material exhibited a CO2 adsorption capacity of up to 55.24 cm(3) g(-1) and 38.17 cm(3) g(-1) at 273 K and 298 K, respectively. In a heterogeneous photocatalytic system of CO2 reduction, this material, co-operated with a ruthenium-based photosensitizer, can efficiently realize CO2 to CO conversion. Under visible-light irradiation for 3 hours, 39.36 mu mol CO and 28.13 mu mol H-2 were obtained. This result is higher than those of most of the reported MOF materials under similar conditions and to the best of our knowledge, this is the first example of a high nuclear MOF used in CO2 reduction. The rooted reasons behind the high reactivity were studied through theoretical calculation studies. The results showed that electrons on reduced [Ru(bpy)(3)]Cl-2 center dot 6H(2)O (bpy = 4,4'-bipyridine) could transfer to the Co-6-MOF and the adsorbed CO2 molecule on the charged Co-6-MOF could be activated more facilely. This work not only clarifies the reasons for high efficiency of the CO2 photoreduction system but also points out to us the direction for designing more effective MOF materials as photocatalysts for artificial CO2 photoreduction.