A covalent organic framework

… inspired by C3N4 for photosynthesis of hydrogen peroxide with high quantum efficiency.

H₂O₂ is not only a green oxidant that widely used in environmental remediation, industrial synthesis, and medical healthcare, etc., but also an emerging energy carrier with a high energy density comparable to compressed H₂. At present, anthraquinone oxidation is still the primary route for large-scale H₂O₂ production, which requires a high energy input and creates a lot of harmful pollutants.

As an alternative, photosynthesis of H₂O₂ from water and O₂ has been considered as a green, safe, and energy-saving strategy for sustainable H₂O₂ production, and has attracted growing interest over the past years. However, the photocatalytic efficiency is still far from meeting the practical requirements. The exploration of efficient semiconductor photocatalysts with superior optoelectronic properties is the key to achieving desirable photocatalytic performance.

Among many candidates, carbon nitride (C₃N₄) has been the main research focus for photocatalytic H₂O₂ synthesis. Specially, the heptazine units in C₃N₄ play a critical role of active sites to facilitate the selective oxygen reduction. Moreover, the metal-free nature of C₃N₄ could also protect the generated H₂O₂ from fast decomposition caused by transition-metal sites like in inorganic semiconductors. However, C₃N₄ photocatalysts usually suffer from narrow light absorption and fast charge recombination due to insufficient conjugation, leading to unsatisfactory photocatalytic performance.

On the basis of the understanding of the inherent merits and pitfalls of C₃N₄, Prof. Yanguang Li from Soochow University, China and his coworkers proposed a new photocatalyst design strategy that integrating the active heptazine units and functional linkers into crystalline conjugated polymer frameworks. The highly conjugated molecular structure could improve the electron delocalization thorough the organic skeletons and increase the light absorption; furthermore, the ordered interlayer π-π would provide high-speed channels for charge transfer, thereby decreasing their recombination.

By comparison with the pristine C₃N₄, the resultant sample (denoted as COF-TpHt) exhibits a broader light absorption up to 800 nm and much improved charge separation efficiency as demonstrated by a series of spectroscopic measurements. Under the visible-light irradiation, COF-TpHt exhibits a high H₂O₂ production rate of 11986 μmol h^–1 g^–1 and an apparent quantum efficiency (AQE) up to 38% at 420 nm, both of which are superior to other reported organic and inorganic counterparts. Impressively, COF-TpHt shows excellent stability that enables almost linear H₂O₂ accumulation during a long time irradiation, giving rise to a H₂O₂ concentration of over 59 mM after 30 h. This research has been published in Chinese Journal of Catalysis (https://doi.org/10.1016/S1872-2067(22)64205-0).

This work was supported by the National Natural Science Foundation of China (22002100, U2002213), the Natural Science Foundation of Jiangsu Province (BK20220027), Collaborative Innovation Center of Suzhou Nano Science and Technology, the 111 Project and Joint International Research Laboratory of Carbon‐Based Functional Materials and Devices.

About the Journal

Chinese Journal of Catalysis is co-sponsored by Dalian Institute of Chemical Physics, Chinese Academy of Sciences and Chinese Chemical Society, and it is currently published by Elsevier group. This monthly journal publishes in English timely contributions of original and rigorously reviewed manuscripts covering all areas of catalysis. The journal publishes Reviews, Accounts, Communications, Articles, Highlights, Perspectives, and Viewpoints of highly scientific values that help understanding and defining of new concepts in both fundamental issues and practical applications of catalysis. Chinese Journal of Catalysis ranks among the top two journals in Applied Chemistry with a current SCI impact factor of 12.92. The Editors-in-Chief are Profs. Can Li and Tao Zhang.

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