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Synthesis of covalent triazine-based frameworks with high CO2 adsorption and selectivity

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      Abstract

      PCTF-4 with benzothiadiazole exhibited the highest CO 2 uptake (20.5 wt%) and CO 2/N 2 selectivity (56) among the reported covalent triazine-based frameworks.

      Abstract

      Four covalent triazine-based frameworks (PCTF-1 to PCTF-4) with triphenylamine as the core were synthesized by a consolidated ionothermal reaction between aromatic nitriles under the catalysis of ZnCl 2. The Brunauer–Emmett–Teller (BET) specific surface area values of PCTF-1 (853 m 2 g −1), PCTF-2 (811 m 2 g −1) and PCTF-3 (391 m 2 g −1) are gradually decreased when increasing the length of branched arm. It indicates that PCTF using monomers with longer branches can be packed more efficiently, resulting in higher density and lower surface area. PCTF-4, compared with PCTF-2, just has the middle benzene of the branches replaced with benzothiadiazole, however N 2 adsorption isotherms showed that its BET specific surface area value (1404 m 2 g −1) is the highest among the PCTFs, almost two times that of PCTF-2. The nitrogen-rich characteristics of C 3N 3 triazine rings result in the frameworks’ strong affinity for CO 2 and thereby high CO 2 adsorption capacity. In particular PCTF-4 with benzothiadiazole exhibited the highest CO 2 uptake (20.5 wt%) at 273 K and 1 bar, this value is one of the highest reported values for covalent triazine-based frameworks. The results demonstrate that the introduction of strong polar groups (benzothiadiazole) into a polymer skeleton is an efficient strategy to produce CO 2-philic microporous organic polymers with enhanced binding affinity to CO 2 molecules. In addition, such PCTFs with high physical–chemical stability and comparable BET surface areas exhibited ideal CO 2/N 2 selectivities (14–56) and CO 2/CH 4 selectivities (11–20) at 273 K, showing that these materials are potential candidates for gas storage and separation. However, in the presence of water vapor, the CO 2 uptake of all polymers decreased probably due to the formation of hydrogen bonds with water, suggesting that materials that perform well under dry conditions may deteriorate under practical conditions.

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      Most cited references 66

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      Reporting physisorption data for gas/solid systems with special reference to the determination of surface area and porosity (Recommendations 1984)

       K. S. W. Sing (1985)
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        Porous, Covalent Triazine-Based Frameworks Prepared by Ionothermal Synthesis

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          Storage of hydrogen, methane, and carbon dioxide in highly porous covalent organic frameworks for clean energy applications.

          Dihydrogen, methane, and carbon dioxide isotherm measurements were performed at 1-85 bar and 77-298 K on the evacuated forms of seven porous covalent organic frameworks (COFs). The uptake behavior and capacity of the COFs is best described by classifying them into three groups based on their structural dimensions and corresponding pore sizes. Group 1 consists of 2D structures with 1D small pores (9 A for each of COF-1 and COF-6), group 2 includes 2D structures with large 1D pores (27, 16, and 32 A for COF-5, COF-8, and COF-10, respectively), and group 3 is comprised of 3D structures with 3D medium-sized pores (12 A for each of COF-102 and COF-103). Group 3 COFs outperform group 1 and 2 COFs, and rival the best metal-organic frameworks and other porous materials in their uptake capacities. This is exemplified by the excess gas uptake of COF-102 at 35 bar (72 mg g(-1) at 77 K for hydrogen, 187 mg g(-1) at 298 K for methane, and 1180 mg g(-1) at 298 K for carbon dioxide), which is similar to the performance of COF-103 but higher than those observed for COF-1, COF-5, COF-6, COF-8, and COF-10 (hydrogen at 77 K, 15 mg g(-1) for COF-1, 36 mg g(-1) for COF-5, 23 mg g(-1) for COF-6, 35 mg g(-1) for COF-8, and 39 mg g(-1) for COF-10; methane at 298 K, 40 mg g(-1) for COF-1, 89 mg g(-1) for COF-5, 65 mg g(-1) for COF-6, 87 mg g(-1) for COF-8, and 80 mg g(-1) for COF-10; carbon dioxide at 298 K, 210 mg g(-1) for COF-1, 779 mg g(-1) for COF-5, 298 mg g(-1) for COF-6, 598 mg g(-1) for COF-8, and 759 mg g(-1) for COF-10). These findings place COFs among the most porous and the best adsorbents for hydrogen, methane, and carbon dioxide.
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            Author and article information

            Journal
            PCOHC2
            Polymer Chemistry
            Polym. Chem.
            Royal Society of Chemistry (RSC)
            1759-9954
            1759-9962
            2015
            2015
            : 6
            : 42
            : 7410-7417
            10.1039/C5PY01090J
            © 2015
            Product
            Self URI (article page): http://xlink.rsc.org/?DOI=C5PY01090J

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