3D N-heterocyclic covalent organic frameworks for urea photosynthesis from NH<sub>3</sub> and CO<sub>2</sub>.

Li, Ning; Zhang, Jiale; Xie, Xiangdong; Wang, Kang; Qi, Dongdong; Liu, Jiang; Lan, Ya-Qian; Jiang, Jianzhuang · Nat Commun · 2025

basic_science · Level V

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Abstract

Artificial photosynthesis of urea from NH<sub>3</sub> and CO<sub>2</sub> seems to remain still essentially unexplored. Herein, three isomorphic three-dimensional covalent organic frameworks with twofold interpenetrated ffc topology are functionalized by benzene, pyrazine, and tetrazine active moieties, respectively. A series of experiment results disclose the gradually enhanced conductivity, light-harvesting capacity, photogenerated carrier separation efficiency, and co-adsorption capacity towards NH<sub>3</sub> and CO<sub>2</sub> in the order of benzene-, pyrazine-, and tetrazine-containing framework. This in turn endows tetrazine-containing framework with superior photocatalytic activity towards urea production from NH<sub>3</sub> and CO<sub>2</sub> with the yield of 523 μmol g<sup>-1</sup> h<sup>-1</sup>, 40 and 4 times higher than that for benzene- and pyrazine-containing framework, respectively, indicating the heterocyclic N microenvironment-dependent catalytic performance for these three photocatalysts. This is further confirmed by in-situ spectroscopic characterization and density functional theory calculations. This work lays a way towards sustainable photosynthesis of urea.