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

Zhao, Jiao, Wang, Qi, Sun, Chunyi, Zheng, Tiantian, Yan, Likai, Li, Mengting, Shao, Kuizhan, Wang, Xinlong, Su, Zhongmin
Journal of materials chemistry A 2017 v.5 no.24 pp. 12498-12505
adsorption, carbon dioxide, carbon monoxide, cobalt, coordination polymers, electrons, energy, global warming, hydrogen, irradiation, light, photocatalysis, photocatalysts, photosensitizing agents
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 (Co₆–MOF) with high nuclearity Coᴵᴵ clusters has been synthesized. This material exhibited a CO₂ adsorption capacity of up to 55.24 cm³ g⁻¹ and 38.17 cm³ 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 μmol CO and 28.13 μmol H₂ 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]Cl₂·6H₂O (bpy = 4,4′-bipyridine) could transfer to the Co₆–MOF and the adsorbed CO₂ molecule on the charged Co₆–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.