Ionic Liquid-Confined Covalent-Organic Framework Pores as Nanoreactors for CO₂ Photoconversion

The topological nanopores of covalent organic frameworks (COFs) show promise as spatially confined nanoreactors for solar CO₂ photoconversion. However, simultaneously increasing the electron density, improving the electron transfer, CO₂ capture, and catalytic efficiency within nanopores remains a challenge for optimizing the performance of such nanoreactors. Here, micro- and mesoporous triazine-COFs were in situ grown on amino-modified BiVO₄ nanosheets (BVO), respectively, obtaining two-dimensional heterojunctions. A highly active ionic liquid (IL) 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][NTf₂]) was subsequently confined within COF nanopores. Adopting IL-confined COF mesopore-nanoreactors, the best nanocomposite enables a 38-fold photoactivity enhancement compared to BVO and 100% selectivity towards CO and CH₄ in pure water under UV-vis light irradiation, resulting in the record apparent quantum yield of 12.7% in visible region. Such performance is due to increased electron density inside mesopores via Z-scheme charge separation between BVO and COF, and the nanoconfinement effects of mesopores for IL, leading to i) facilitated directed electron transfer from COF to IL via multi-hydrogen bonds between the triazine acceptors and [EMIM]⁺ cations, ii) promoted CO₂ capture by redistribution of IL ions, and iii) easy activation of CO₂ molecules owing to shortened distance to adjacent [EMIM]⁺ cations as catalytic sites and reduced relative orientation angle.