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

Abstract

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.