关键词: 离子热反应, 多孔芳香材料, CO₂选择性吸附, 富氮骨架

In this report, novel porous aromatic frameworks (PAF-51) have been synthesized using tetrahedral units in the presence of zinc chloride by a facile ionothermal method. PAF-51-1 and PAF-51-2 displayed large surface areas as 720 and 557 m²·g^-1 (BET) respectively. Selectivity of CO₂/N₂ is as high as 52.2 at 273 K and CO₂/CH₄ can reach 10.3 at 273 K. The properties make it a promise as the ideal candidate to capture CO₂ and can be used for clean and renewable energy which still needs further study. FTIR spectra of initial monomers and final products gave us information of the reaction process. The absence of cyanogroups (2230 cm^-1) of the TCDPSi can verify the completion of the trimerization reaction. The appearance of breathing vibration bands of triazine ring (1560～1520 and 1480～1350 cm^-1) and out-of-plane flexural vibration (860～736 cm^-1) indicate the formation of polymeric networks. Thermogravimetric analysis (TGA) under atmosphere of the two samples revealed a high thermal stability up to 415 (PAF-51-1) and 475 ℃ (PAF-51-2). Furthermore, these materials are all insoluble after long-period stirring in most common solvents, such as 1 mol/L HCl, acetone, tetrahydrofuran (THF), N,N-dimethylformamide (DMF), CHCl₃, etc., showing high chemical stability. FTIR spectra of PAF-51 before stirring in these solvents (HCl, acetone, THF, DMF, and CHCl₃ etc.) and after stirring in solvents were barely changed. Powder X-ray diffraction (PXRD) of these PAFs revealed no distinct diffraction peaks, indicating that these polymers are composed of an amorphous network. Scanning electron microscopy (SEM) analyses display that the polymers consist of aggregated irregular lumps with nanometer dimensions. Transmission electron microscopy (TEM) investigations show their clear porous textures and agree on the amorphous structures. The surface areas of PAF-51-1 and PAF-51-2 are 720 and 557 m²·g^-1 on BET model respectively. At low relative pressure, inflection point of the isotherm of PAF-51-2 appears much earlier than PAF-51-1, which might be a suggestion of the distribution of micropores in the product. Indeed, pore size distribution calculated from nonlocal density functional theory (NLDFT) using the model of carbon as an adsorbent also demonstrates this. The pore size distribution of PAF-51-1 mainly exists in the region between 2～20 Å. Although pore size distribution of PAF-51-2 also mostly exists in the microporous region, less distribution than that in PAF-51-1, and more distribution can be found in mesoporous region between 20～500 Å. The selectivity of PAF-51-1 reaches 34.1 which was calculated from the initial slopes of the CO₂ and N₂ adsorption isotherms. Much more remarkably, the selectivity at room temperature (298 K) decreases very little (from 34.1 to 32.4), which is better than many other porous materials with higher surface area and CO₂ uptakes. Remarkably, the selectivity of PAF-51-2 is much higher than PAF-51-1 (52.2 at 273 K and 43.6 at 298 K). Likewise, the selective adsorption of CO₂ to CH₄ can reach 10.3 at 273 K.

Key words: ionothermal reaction, porous aromatic framework, CO₂ adsorption separation, nitrogen-rich framework