Synthesis, characterization, and gas (SO₂, CO₂, NO₂, CH₄, CO, NO, and N₂) adsorption properties of the CTF-1 covalent triazine framework-based porous polymer: experimental and DFT studies

In this study, a covalent-triazine framework (i.e., CTF-1) was synthesized through the ionothermal cyclotrimerization method utilizing 1,4-dicyanobenzene (DCB) as the monomer and molten ZnCl₂ as both the solvent and Lewis acid catalyst at 400 ℃. The obtained microporous crystalline material was systematically characterized by employing Fourier-transform infrared (FT-IR) spectroscopy, powder X-ray diffraction (PXRD), N₂ adsorption–desorption isotherms (BET-NLDFT surface area-pore size measurements), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM), solid-state ¹³C NMR spectroscopy, elemental analysis (EA), and thermogravimetric analysis (TGA). The adsorption equilibrium and kinetic data for SO₂, CO₂, NO₂, CH₄, CO, NO, and N₂ gases onto the surfaces of CTF-1 were volumetrically measured at 25 and 35 ℃ and gas pressures of up to 1 bar. To systematically realize the gas adsorption characteristics of CTF-1, various isotherm models, including the Langmuir, Sips, and Toth models, were employed to correlate the experimental adsorption isotherms. Besides, different kinetic models such as pseudo-first-order (PFO), pseudo-second-order (PSO), and fractal-like pseudo-first-order (FL-PFO) models were applied to analyze the experimental adsorption kinetic data. In the meantime, to further investigate the adsorption mechanism of gases upon the CTF-1 surface, density-functional theory (DFT) calculations were performed at ωB97XD level of theory.