Photocatalytic CO2 reduction catalyzed by metalloporphyrin: Understanding of cobalt and nickel sites in activity and adsorption

Porphyrin based MOFs have exhibited excellent photocatalytic properties in photocatalytic CO2 reduction and metal sites in porphyrin units play an important role in the reactions. For investigating the mechanism of different photocatalytic performance of metals sites in porphyrin units, metalloporphyrin complexes with Co and Ni metal sites (Co-POR, Ni-POR) were prepared by a short term method and used for visible-light drived CO2 photoreduction conversion with water vapor as sacrificial agent. PL spectra indicates that the fluorescence intensity of Co-POR was obviously lower than that of Ni-POR and DFT calculation indicates that CO2 adsorption energy on Co-POR (17.92 kJmol(-1)) is higher than that on Ni-POR (16.37 kJmol(-1)). The efficient separation of charge carries and the strong CO2 adsorption ability are main advantages of Co-POR compared with Ni-POR. As a direct result, the experimental results showed that 0.40 mu molg(-1)h(-1) CO was produced over Co-POR after 4 h reaction, which is about equivalent to a 1.7-fold enhancement compared to Ni-POR under the same reaction condition.