Visible-Light-Driven Reduction of CO2 to CO with Highly Active and Selective Earth-Abundant Metal Porphyrin-Conjugated Organic Polymers.

ABSTRACT

The field of artificial photosynthesis, which focuses on harnessing solar light for the conversion of CO2 to economically valuable chemical products, remains a captivating area of research. In this study, we developed a series of photocatalysts based on Earth abundant elements (Fe, Co, Ni, Cu, and Zn) incorporated into 2D metalloporphyrin-conjugated organic polymers known as MTBPP-BEPA-COPs. These photocatalysts were utilized for the photoreduction of CO2 employing only H2O as the electron donor, without the need for any sacrificial agents or precious-metal cocatalysts. Remarkably, all of the synthesized MTBPP-BEPA-COPs exhibited an exceptional CO2 photoreduction performance only irradiated by visible light. Particularly, upon optimizing the metal ion coordinated with porphyrin units, ZnTBPP-BEPA-COP outperformed the other MTBPP-BEPA-COPs in terms of photocatalytic activity, achieving an impressive CO reduction yield of 152.18 µmol g-1 after just 4 h of irradiation. The electrostatic potential surfaces calculated by density functional theory suggest the potential involvement of metal centers as binding and catalytic sites for the binding of CO2. The calculated adsorption energy of CO2 with ZnTBPP-BEPA-COP exhibited one of the two smallest values. This may be the reason for the excellent catalytic effect of ZnTBPP-BEPA-COP. Thus, the present study not only demonstrates the potential of porphyrin-based conjugated polymers as highly efficient photocatalysts for CO2 reduction but also offers valuable insights into the rational design of such materials in the future.