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

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 ZnCl2 (Lewis acid condition) and CF3SO3H (strong Bronsted acid condition). From N-2 adsorption isotherms, the Lewis acid condition gives higher surface areas than the strong Bronsted acid condition. The amorphous nano-to microporous frameworks (>50% micropore fraction) exhibit excellent thermal stabilities (>450 degrees C) with BET surface areas up to 1180 m(2) g(-1). A very similar ultramicropore size distribution between 4 and 10 angstrom was derived from CO2 adsorption isotherms with a "CO2 on carbon based slit-pore model". At 1 bar the gases H-2 (at 77 K), CO2 (at 273 and 293 K) and CH4 (at 273 K) are adsorbed up to 1.24 wt%, 58 cm(3) g(-1) and 20 cm(3) g(-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 CO2: N-2, CO2:CH4 and CH4:N-2 selectivity values of up to 41 : 1, 7 : 1 and 6 : 1, respectively, are calculated for p -> 0 at 273 K. The adamantane PCTFs have isosteric heats of adsorption for CO2 of 25-28 kJ mol(-1) at zero loading and most of them also > 25 kJ mol(-1) over the entire adsorption range which is well above the heat of liquefaction of bulk CO2 or the isosteric enthalpy of adsorption for CO2 on activated carbons.