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 powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FT-IR), solid-state ¹³C nuclear magnetic resonance (NMR), scanning electron microscope (SEM), high resolution transmission electron microscope (HR-TEM), diffuse reflection spectroscopy (DRS) and cyclic voltammetry (CV). BL-TF-COF presents high crystallinity, large 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.