3D N-heterocyclic covalent organic frameworks for urea photosynthesis from NH3 and CO2

Abstract

Abstract Artificial photosynthesis of urea from NH3 and CO2 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 NH3 and CO2 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 NH3 and CO2 with the yield of 523 μmol g−1 h−1, 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.