Highly Efficient and Selective Visible-Light Driven CO Reduction by Two Co-Based Catalysts in Aqueous Solution.

Photocatalytic CO reduction has been considered as a promising approach to solve energy and environmental problems. Nevertheless, developing inexpensive photocatalysts with high efficiency and selectivity remains a big challenge. In this study, two Co-based complexes [Co(L)Cl] () and [Co(L)Cl] () were synthesized by treating two DPA-based (DPA: dipicolylamine) ligands with Co, respectively. Under visible-light irradiation, the performance of as a homogeneous photocatalyst for CO reduction in aqueous media has been explored by using [Ru(phen)] as a photosensitizer, and triethylolamine (TEOA) as a sacrificial reductant. shows high photocatalytic activity for CO-to-CO conversion, corresponding to the high TON of 2600 and TOF of 260 h (TON = turnover number for CO; TOF = turnover frequency for CO). High selectivity of 97% for CO formation is also achieved. The control experiments catalyzed by demonstrated that two Co(II) centers in may operate independently and activate one CO molecule each. Furthermore, the proposed mechanism of for photocatalytic CO reduction has been investigated via electrochemical analysis, a series of quenching experiments, and density functional theory calculations.