Post synthesis of a glycine-functionalized covalent triazine framework with excellent CO2 capture performance

Abstract In this article, carbonyl-appended covalent triazine frameworks (CTFs) were prepared by ionothermal trimerization of bis(4-cyanophenly)ketone in molten ZnCl2. To take advantage of the strengths of both CTFs and amino acids for CO2 capture, an amino acid functionalized CTF (BCK-CTF-Gly) was achieved for the first time through post-synthetic modification of a carbonyl-appended CTF (BCK-CTF-400-5) by glycine. The chemical structures of BCK-CTF-400-5 and BCK-CTF-Gly were examined by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy, and solid-state CP/MAS 13C NMR. The content of the grafting carboxyl groups in BCK-CTF-Gly was determined to be ca. 2.3 mmol/g. Both exhibit large BET surface areas (over 1700 m2/g) and BCK-CTF-Gly has an increased ratio of micropore volumes (from 35% to 50%) due to the grafting glycine moieties onto pore walls. Compared with the pristine BCK-CTF-400-5, the glycine-functionalized BCK-CTF-Gly exhibits an exceptionally high CO2 uptake of 245 mg/g at 1 bar and 273 K, which belongs to the top level among the reported CTFs. In situ FTIR spectra were recorded to examine the CO2 adsorption process of BCK-CTF-Gly. Additionally, BCK-CTF-Gly presents the Qst value of 33.3 kJ/mol and a high CO2/N2 selectivity of 35 at 298 K as calculated by the IAST model. The desorption is easy and BCK-CTF-Gly exhibits stable CO2 uptake performance over ten adsorption-desorption cycles. All these results suggest that the introduction of amino acids onto pore walls of CTFs shows good potential for CO2 capture.