Highly stable nanoporous covalent triazine-based frameworks with an adamantane core for carbon dioxide sorption and separation

• Published in: Journal of materials chemistry. A, Materials for energy and sustainability Materials for energy and sustainability, 2013-11, Vol.1 (47), p.14990-14999
• Main Authors: Bhunia, Asamanjoy, Boldog, Ishtvan, Moller, Andreas, Janiak, Christoph
• Format: Article
• Language: English
• Subjects: Adsorption; Carbon dioxide; Covalence; Isotherms; Lewis acid; Nanostructure; Surface area; Surface chemistry
• ISSN: 2050-7488; 2050-7496
• DOI: 10.1039/c3ta13407e

Adamantane substituted with two to four 4-cyanophenyl groups was used for preparation of a new series of robust Porous Covalent Triazine-based Framework (PCTF) materials. Novel adamantane PCTFs were synthesized in good yields (>80%) by the trimerization reaction of 1,3-bis-, 1,3,5-tris- and 1,3,5,7-tetrakis(4-cyanophenyl)adamantane, respectively, in the presence of ZnCl sub(2) (Lewis acid condition) and CF sub(3)SO sub(3)H (strong Broensted acid condition). From N sub(2) adsorption isotherms, the Lewis acid condition gives higher surface areas than the strong Broensted acid condition. The amorphous nano- to microporous frameworks (>50% micropore fraction) exhibit excellent thermal stabilities (>450 degree C) with BET surface areas up to 1180 m super(2) g super(-1). A very similar ultramicropore size distribution between 4 and 10 Aa was derived from CO sub(2) adsorption isotherms with a "CO sub(2) on carbon based slit-pore model". At 1 bar the gases H sub(2) (at 77 K), CO sub(2) (at 273 and 293 K) and CH sub(4) (at 273 K) are adsorbed up to 1.24 wt%, 58 cm super(3) g super(-1) and 20 cm super(3) g super(-1), respectively. Gas uptake increases with BET surface area and micropore volume which in turn increase with the number of cyano groups in the monomer. From single component adsorption isotherms, IAST-derived ideal CO sub(2):N sub(2), CO sub(2):CH sub(4) and CH sub(4):N sub(2) selectivity values of up to 41 : 1, 7 : 1 and 6 : 1, respectively, are calculated for p arrow right 0 at 273 K. The adamantane PCTFs have isosteric heats of adsorption for CO sub(2) of 25-28 kJ mol super(-1) at zero loading and most of them also >25 kJ mol super(-1) over the entire adsorption range which is well above the heat of liquefaction of bulk CO sub(2) or the isosteric enthalpy of adsorption for CO sub(2) on activated carbons.