Effect of Different Functional Groups on Photocatalytic Hydrogen Evolution in Covalent‐Organic Frameworks

Abstract

Covalent‐organic frameworks (COFs) have been recognized as a new type of promising photocatalysts for hydrogen evolution. To investigate how different functional groups attached in the backbone of COFs affect the overall photocatalytic H 2 evolution, for the first time, we selected and synthesized a series of ketoenamine‐based COFs with the same host framework as model system. It includes TpPa−COF−X (X=−H, −(CH 3)2, and −NO 2) with three different groups attached in the backbone of TpPa−COF. We systematically investigated the differences in morphology, light‐absorption intensity and band gap of these 2D COFs. The results of photocatalytic H 2 evolution measurements indicate that the TpPa−COF−(CH 3)2 shows the best activity, while the activity of TpPa−COF−NO 2 is relatively low compared to that of other two COFs in the system. Moreover, the separation ability of photogenerated charge was also followed the order of TpPa−COF−(CH 3)2>TpPa−COF>TpPa−COF−NO 2. The best photocatalytic H 2 production performance of TpPa−COF−(CH 3)2 in these systems should be mainly attributed to the better electron‐donating ability of −CH 3 groups compared to −H or −NO 2 group, which result in more efficient charge transferring in the inner of the material. This work demonstrates that reasonably adding electron‐donating group in TpPa−COFs can lead to a better photocatalytic H 2 evolution activity, and which is meaningful for further design of efficient COF‐based photocatalysts for H 2 evolution.