Single-atom Cu sites on covalent organic frameworks with Kagome lattices for visible-light-driven CO2 reduction to propylene

CO to multicarbon fuels via photocatalytic conversion, especially propylene, is a viable pathway, but propylene remains unreported due to the two C-C coupling with the eighteen-electron reduction process. Herein, [1,1′-biphenyl]-3,3′,5,5′-tetracarbaldehyde, and [2,2-bipyridine]-5,5-diamine units were condensed and synthesized in combination with a post-modification strategy, named BTA-COF-M (M = H, Cu, Fe, Co, Ni or Zn). BTA-COF-Cu has distinct kagome lattices and abundant exposed-atom Cu sites, which can induce CO to undergo two C-C couplings into CH products under visible light illumination. According to experimental and theoretical analyses, the outstanding performance of BTA-COF-Cu can be attributed to the ideal synergistic contribution of the Kagome lattices and the atomic Cu active sites, which promote CO adsorption/activation, facilitate photoexcited charge carrier dynamics, and induce secondary coupling of key intermediates. This research provides an innovative perspective for the construction of Kagome lattice COF with monatomic metal sites for CO reduction to high value-added propylene.