Search

Covalent organic frameworks (COFs) have gained significant attention as key photocatalysts for efficient solar light conversion into hydrogen production. Unfortunately, the harsh synthetic conditions and intricate growth process required to obtain highly crystalline COFs greatly hinder their practical application. Herein, we report a simple strategy for the efficient crystallization of 2D COFs based on the intermediate formation of hexagonal macrocycles. Mechanistic investigation suggests that the use of 2,4,6‐triformyl resorcinol (TFR) as the asymmetrical aldehyde build block allows the equilibration between irreversible enol‐to‐keto tautomerization and dynamic imine bonds to produce the hexagonal β‐ketoenamine‐linked macrocycles, the formation of which could provide COFs with high crystallinity in half hour. We show that COF‐935 with 3 wt % Pt as cocatalyst exhibit a high hydrogen evolution rate of 67.55 mmol g−1 h−1 for water splitting when exposed to visible light. More importantly, COF‐935 exhibits an average hydrogen evolution rate of 19.80 mmol g−1 h−1 even at a low loading of only 0.1 wt % Pt, which is a significant breakthrough in this field. This strategy would provide valuable insights into the design of highly crystalline COFs as efficient organic semiconductor photocatalysts. [ABSTRACT FROM AUTHOR]

Photocatalysis is considered to be one of the most effective methods to solve the global energy problem. Therefore, it is essential to clarify the principles of the design and synthesis of highly effective photocatalysts. In this paper, we report a series of covalent organic frameworks (denoted as COF-960-n) with different degrees of intralayer hydrogen-bonding interactions via a multivariate synthetic strategy. Although the resultant COFs have similar chemical structures, good crystallization, and high surface area, the overall photocatalytic hydrogen evolution changed significantly due to the different ratios of hydroxyl to methoxy groups. COF-960-5 exhibited the best charge transfer rate and the lowest electron–hole recombination rate, resulting in the best hydrogen evolution rate (678 μmol g−1 h−1) under visible light irradiation. Moreover, the hydrogen-bonding interactions help to enhance the stability of COFs during photocatalysis. This study demonstrates that partial H-bonding can lead to a better photocatalytic H2 evolution, providing insight into the further design of efficient COF-based photocatalysts for H2 evolution. [ABSTRACT FROM AUTHOR]

Imine‐linked covalent organic frameworks (COFs) have been extensively studied in photocatalysis because of their easy synthesis and excellent crystallinity. The effect of imine‐bond orientation on the photocatalytic properties of COFs, however, is still rarely studied. Herein, we report two novel COFs with different orientations of imine bonds using oligo(phenylenevinylene) moieties. The COFs showed similar structures but great differences in their photoelectric properties. COF‐932 demonstrated a superior hydrogen evolution performance compared to COF‐923 when triethanolamine was used as the sacrificial agent. Interestingly, the use of ascorbic acid led to the protonation of the COFs, further altering the direction of electron transfer. The photocatalytic performances were increased to 23.4 and 0.73 mmol g−1 h−1 for protonated COF‐923 and COF‐932, respectively. This study provides a clear strategy for the design of imine‐linked COF‐based photocatalysts and advances the development of COFs. [ABSTRACT FROM AUTHOR]