Catechol-functionalized Covalent Organic Framework: Synthesis, Characterization and Metal-free Organocatalyst for CO2 Fixation under Mild Conditions.

Covalent organic frameworks (COFs) incorporating hydrogen bond donor (HBD) moieties show great promise for heterogeneous catalyst for CO2 cycloaddition. In this work, a catechol-functionalized COF (BL-TF-COF) was constructed via Schiff-base condensation under solvothermal conditions, which was characterized using PXRD, FT-IR, solid-state 13C NMR, SEM, HR-TEM, DRS and CV. BL-TF-COF presents high crystallinity, large BET surface area (523 m2 g-1) and remarkable chemical stability, along with abundant hydroxyl functional groups distributed on the pore wall. This framework shows a CO2 adsorption capacity up to 88 mg g-1 at 273 K and 1 bar. The binding locations of the adsorption of CO2 over BL-TF-COF was studied by grand canonical Monte Carlo (GCMC) simulations. BL-TF-COF displays remarkable catalytic performance for the cycloaddition of CO2 with epoxides under mild conditions. Under the condition of the epichlorohydrin/tetrabutylammonium bromide/BL-TF-COF molar ratio of 10210:630:4, the system achieved 62.5% substrate conversion at 25°C under atmospheric CO2 pressure (1 bar) within 48 h. Mechanistic insights into epoxide adsorption and activation processes were investigated through density functional theory (DFT) calculations.