Imine-linked covalent organic frameworks (COFs) have been widely studied in the field of photocatalytic hydrogen production due to their easy synthesis, good crystallinity, tunable pore size and excellent thermal and chemical stability. However, the effect of substituent type on the photocatalytic properties of COFs has been rarely studied. Herein, six COFs with COF-TpPa as the basic skeleton were synthesized by introducing different types of substituents in the p-phenylenediamine benzene ring, among which TpPa-CN₂ was prepared for the first time. The COFs showed similar structures but great differences in their photoelectric properties. TpPa-Cl₂ and TpPa-CN₂ demonstrated a superior hydrogen evolution performance compared to the other four COFs when ascorbic acid was used as the electron sacrificial agent and Pt as the cocatalyst. The photocatalytic hydrogen evolution (PHE) rate of TpPa-Cl₂ and TpPa-CN₂ was as high as 99.23 and 76.93 mmol g⁻¹ h⁻¹, respectively. The introduction of chlorine and cyanide improved the visible-light response, hydrophilicity and photo-carrier separation ability of TpPa COF, which contributed to the enhanced PHE efficiency of TpPa-Cl₂ and TpPa-CN₂. This study provides a strong basis for the systematic fine-tuning of the structural and physico-chemical properties of COFs aiming to achieve COF materials with ultra-high photocatalytic activity.

中文翻译：

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共价有机骨架中光催化析氢性能的显着改善：取代基微调

亚胺连接的共价有机骨架（COF）由于其易于合成、良好的结晶度、可调的孔径以及优异的热稳定性和化学稳定性，在光催化制氢领域得到了广泛的研究。然而，取代基类型对COFs光催化性能的影响却鲜有研究。本文通过在对苯二胺苯环上引入不同类型的取代基，合成了以COF-TpPa为基本骨架的6种COF ，其中TpPa-CN ₂为首次制备。 COF表现出相似的结构，但光电特性存在很大差异。当使用抗坏血酸作为电子牺牲剂和Pt作为助催化剂时，TpPa-Cl ₂和TpPa-CN _{2与其他四种COF相比表现出优异的析氢性能。 TpPa-Cl 2}和TpPa-CN ₂的光催化析氢(PHE)速率分别高达99.23和76.93 mmol g ^-1 h ^-1。氯和氰化物的引入改善了TpPa COF的可见光响应、亲水性和光载流子分离能力，这有助于提高TpPa-Cl ₂和TpPa-CN ₂的PHE效率。该研究为系统地微调COF的结构和物理化学性质，以实现具有超高光催化活性的COF材料提供了坚实的基础。