ZIF-8/covalent organic framework for enhanced CO2 photocatalytic reduction in gas-solid system

It remains challenging to design and synthesize porous crystalline photocatalysts for photocatalytic reduction CO2 with high efficiency. Herein, a Schiff-based covalent organic framework (TpPa-1) is explored to combine with a metal–organic framework (ZIF-8) via a simple and fast method (the grinding method) firstly, generating a series of photocatalysts TpPa/ZIF-8. The photocatalytic performances of the as-synthesized photocatalysts TpPa/ZIF-8 are evaluated through a gas–solid reaction mode without photosensitizers and sacrificial agents, exhibiting excellent photocatalytic activities toward CO2 in pure CO2 and 10% CO2 atmosphere, especially in 10% CO2 environment. Therefore, the experimental result presents that TpPa/ZIF-8 can obtain the CO formation rates of 43.94 μmol·g−1·h−1 at a pure CO2 environment and 84.87 μmol·g−1·h−1 in 10% CO2 atmosphere, approximately 2 times and about 6 times larger than those of TpPa-1 in the pure CO2 and 10% CO2 atmosphere, respectively. The interesting phenomenon inspires us to investigate the structural factors affecting the photocatalytic activity, and hydroxyl groups from TpPa-1 are suspected to play an important role in the significantly improved photoreduction performance of CO2 in 10% CO2 atmosphere. The controlling examples TFPa/ZIF-8 without hydroxyl groups have also been prepared and evaluated their photoreduction performances in order to validate this hypothesis. The results clearly prove the hydroxyl groups tend to enhance CO2 photoreduction. Additionally, it is noted that TpPa/ZIF-8 could maintain certain photocatalytic activity under the irradiation of sunlight. Summarily, the superior photocatalytic performances of TpPa/ZIF-8 may result from the high charge separation efficiency and increased photocatalytic active sites as well as the CO2 adsorption capacity. The reported work sheds light on the construction of MOFs/COFs hybrid materials and expands their applications.