Encapsulation of Co single sites in covalent triazine frameworks for photocatalytic production of syngas

The photocatalytic production of syngas using a noble-metal-free catalytic system is a promising approach for renewable energy and environmental sustainability. In this study, we demonstrate an efficient catalytic system formed by integrating Co single sites, which act as the active sites, in covalent triazine frameworks (CTFs), which act as the photoabsorber, for the photocatalytic production of syngas from CO2 in aqueous solution. The enhanced light absorption of the CTFs, which contain intramolecular heterojunctions, in conjunction with 0.8 mmol L−1 of the Co complex enables excellent syngas production with a yield of 3303 μmol g−1 (CO:H2 = 1.4:1) in 10 h, which is about three times greater than that achieved using CTF without a heterojunction. In the photocatalytic reaction, the coordinated single Co centers accept the photogenerated electrons from the CTF, and serve as active sites for CO2 conversion through an adsorption-activation-reaction mechanism. Theoretical calculations further reveal that the intramolecular heterojunctions highly promote photogenerated charge separation, thus boosting photocatalytic syngas production. This work reveals the promising potential of CTFs for single-metal-site-based photocatalysis.