Template-Free Synthesis of a Highly Porous Benzimidazole-Linked Polymer for CO₂ Capture and H₂ Storage

Unprecedented high-temperature CO2 selectivity in N2-phobic nanoporous covalent organic polymers

“…A smooth adsorption-desorption cycle implies that the interaction between CO 2 and the networks are weak enough to regenerate these azo-COPs without too much energy. Similar behaviour has been reported where adsorption on basic sites do not require heating to regenerate porous polymers 41,44 . The CO 2 isosteric heat of adsorption (Q st ) is calculated from the adsorption data at 263, 273, 298 and 323 K 45 .…”

“…that is, @DDG ads /@T ¼ À DDS ads 4 0, as in most previous temperature-dependent selectivity measurements 2,41,44 . However, the present azo-COPs show the opposite temperature dependence of the CO 2 /N 2 selectivity, suggesting positive DDS ads , that is, the entropy loss in the event of N 2 adsorption should be larger than that associated with the CO 2 adsorption (Supplementary Fig.…”

“…Owing to the presence of an electron-deficient carbon atom, CO 2 is expected to interact with protic electronegative functionalities (for example, amines) leading to a strong chemisorption, while N 2 remains impartial. So far, this simple interaction has led to a plethora of nanoporous polymers where the nitrogen-rich functionalities, such as triazine 1,18 , tetrazole 3 , imidazole 41 , phosphazene 24 , imide 42 and amines 25,43 , are built in. In all these and many other situations 2 , CO 2 -philicity is the main driving force for the CO 2 /N 2 selectivity, without taking into account any chemical architecture that would repel N 2 molecules selectively.…”

“…For example, covalent triazine-based frameworks (CTFs) reveal a mere CO 2 /N 2 selectivity of 31.2 at 273 K. Our earlier work on triazines 25 leads to the understanding 46 that an imidic bond (-C ¼ N-) is not N 2 -phobic. Benzimidazole-linked polymers 41 show selectivities up to 113 at 273 K, being reduced to 71 at 298 K. Although nitrogen-rich organic cage frameworks 30,47 show high CO 2 /N 2 selectivities up to 213 at 298 K, their surface areas (o10 m 2 g À 1 ) and CO 2 capture capacities (up to 7.15 mg g À 1 ) are very low. Other structures with protic nitrogens also behave in a similar fashion 43,44,48 .…”

Feasibility of CO2 adsorption by solid adsorbents: a review on low-temperature systems

“…The relatively high CO 2 uptake and binding is most likely due to the functional nature of PBIs because of the amphoteric imidazole moieties and favorable interactions of the CO 2 polarizability through hydrogen bonding and dipole-quadrupole interactions that utilize the protonated and proton-free nitrogen sites of imidazole rings, respectively. Rabbani and El-Kaderi (2011) sensitized benzimidazole-linked polymer (BILP-1) by condensation reaction between tetrakis (4-formylphenyl) methane (TFPM) and 2 ,3,6,7,10,, which is believed to be the most porous purely organic benzimidazole-linked polymer reported until now with the BET surface area of 1172 m 2 g -1 .…”