Donor-acceptor moiety functionalized covalent organic frameworks for boosting charge separation and H2 photogeneration.

Covalent organic frameworks (COFs) have a broad prospect to be used as a photocatalytic platform to convert solar energy into valuable chemicals due to their tunable structures and rich active catalytic sites. However, constructing COFs with tuned sp2-carbon donor-acceptor moiety remains an enormous challenge. Herein, we synthesized two new fully π-conjugated cyano-ethylene-linked COFs containing benzotrithiophene as functional group by Knoevenagel polycondensation reaction. The accetpor 2,2'-bipyridine unit in BTT-BpyDAN-COF skeleton favored the formation of a intermolecular specific electron transport pathway with the donor benzotrithiophene, and thereby promoted charge separation and transfer efficiency. Specifically, a donor-acceptor (D-A) type BTT-BpyDAN-COF exhibited high hydrogen evolution rate of 10.1 mmol g-1h-1 and an excellent apparent quantum efficiency of 4.83 % under visible light irradiation.

Recent advances on covalent organic frameworks (COFs) as photocatalysts: different strategies for enhancing hydrogen generation.

The excessive use of traditional fossil fuels has led to energy and environmental pollution problems. Solar-driven hydrogen generation has attracted much attention in recent years owing to its environmental friendliness and economic feasibility. So far, a series of photocatalysts have been advanced. Unfortunately, these photocatalysts face some issues including poor sunlight harvesting ability, weak photo-corrosion resistance, broad band gap, bad stability, inferior hydrogen evolution rate and so on. It just so happens that COFs have emerged to provide an opportunity for settling these issues. Covalent organic frameworks (COFs), a novel family of porous materials with regular porosity and tunable physicochemical structures, have been extensively explored as photocatalysts for hydrogen production. Moreover, their photocatalytic activities are highly structurally dependent. In this review, we mainly focus on the linkage chemistry and disparate strategies for boosting COF-based photocatalytic hydrogen generation performance in detail. The prospects and obstacles confronted in the development of COF-based photocatalysts and proposals to settle dilemmas are also discussed.