Covalently-Bonded Single-Site Ru-N2 Knitted into Covalent Triazine Frameworks for Boosting Photocatalytic CO2 Reduction

Harvesting solar energy to convert CO2 into chemicals via photocatalysis has received increasing attention, however, lack of precisely controlled and uniformly dispersed active sites usually leads to low selectivity and activity. Herein, we present an in situ covalent-bonding strategy for the first time to knit well-defined single-site Ru-N2 into conjugated covalent triazine frameworks (CTFs) for highly selective photoreduction of CO2. The resulting Ru-CTF enhanced charge separation and stabilized the molecular catalyst, providing a solar-to-formate conversion rate of 2090 μmol·gcat−1·h−1 with a selectivity of 98.5 % without extra photosensitizer, which greatly outperforms most other reported photocatalysts. Experiments and DFT calculations demonstrate that the single-site Ru-N2 could easily activate CO2 and the H2O-substituted Ru-N2 unit is the newly discovered active center for the efficient photocatalysis. This work paves a new way and significant understandings to design single-site CTF-based photocatalysts for highly selective CO2 photoreduction.