Covalent Organic Framework Nanosheets Embedding Single Cobalt Sites for Photocatalytic Reduction of Carbon Dioxide
Xiaoyan Wang, Zhiwei Fu, Lirong Zheng, Chengxi Zhao, Xue Wang, Samantha Y. Chong, Fiona McBride, Rasmita Raval, Matthew Bilton, Lunjie Liu, Xiaofeng Wu, Linjiang Chen, Reiner Sebastian Sprick, Andrew I. Cooper
Abstract
Covalent organic framework nanosheets (CONs), fabricated from two-dimensional covalent organic frameworks (COFs), present a promising strategy for incorporating atomically distributed catalytic metal centers into well-defined pore structures with desirable chemical environments. Here, a series of CONs was synthesized by embedding single cobalt sites that were then evaluated for photocatalytic carbon dioxide reduction. A partially fluorinated, cobalt-loaded CON produced 10.1 μmol carbon monoxide with a selectivity of 76%, over 6 hours irradiation under visible light (TON = 28.1), and a high external quantum efficiency (EQE) of 6.6% under 420 nm irradiation in the presence of an iridium dye. The CONs appear to act as a semiconducting support, facilitating charge carrier transfer between the dye and the cobalt centers, and this results in a performance comparable with that of the state-of-the-art heterogeneous catalysts in the literature under similar conditions. The ultrathin CONs outperformed their bulk counterparts in all cases, suggesting a general strategy to enhance the photocatalytic activities of COF materials.