Design of porphyrin-based frameworks for efficient visible light-promoted reduction of CO2 from dilute gas: Combined experimental and theoretical investigation

The photocatalytic carbon dioxide reduction (CO2R) coupled with hydrogen evolution reaction (HER) constitutes a promising step for a sustainable generation of syngas (CO + H2), an essential feedstock for the preparation of several commodity chemicals. Herein, visible light/sunlight-promoted catalytic reduction of CO2 and protons to syngas using rationally designed porphyrin-based 2D porous organic frameworks, POF(Co/Zn) is demonstrated. Indeed, POF(Co) showed superior catalytic performance over the Zn counterpart with CO and H2 generation rates of 1104 and 3981 μmol g−1h−1, respectively. The excellent catalytic performance of Co-based POF is aided by the favorable transfer of photo-excited electrons from Ru-sensitizer to the CoII catalytic site, which is not feasible in the case of POF(Zn), revealed from the theoretical investigation. More importantly, the POF(Co) catalyzes the reduction of CO2 even from dilute gas (13% CO2), surpassing most reported framework-based photocatalytic systems. Significantly, the catalytic performance of POF(Co) was increased under natural sunlight conditions suggesting sunlight-promoted enhancement in syngas generation. The in-depth theoretical investigation further unveiled the comprehensive mechanistic pathway of the light-promoted concurrent CO and H2 generation. This work showcases the advantages of porphyrin-based frameworks for visible light/sunlight-promoted syngas generation by utilizing greenhouse gas (CO2) and protons under mild eco-friendly conditions.