Impact of tailored chemical and textural properties on the performance of nanoporous borazine-linked polymers in small gas uptake and selective binding

Six borazine-linked polymers (BLPs) have been synthesized through the thermolysis reaction of p-phenylenediamine, 1,3,5-tris-(4-aminophenyl)benzene, benzidine, or tetra-(4-aminophenyl)methane with boron tribromide or boron trichloride. Each product exists as an amorphous polymer whose chemical connectivity was confirmed by FT-IR and elemental analysis while thermogravimetric analysis revealed moderate thermal stabilities up to about 200 °C under nitrogen atmosphere. All BLPs possess high surface areas with chlorinated BLPs exhibiting higher values than brominated BLPs (1,174–1,569 vs. 503–849 m2/g, respectively). Gas storage capabilities were investigated as well. BLPs possess good hydrogen uptakes (0.68–1.75 wt% at 77 K) and zero-coverage isosteric heat of adsorption, Q st, (7.06–7.65 kJ/mol) as calculated by the virial method. The uptakes and heat of adsorption for carbon dioxide (51–141 mg/g at 273 K with Q st: 22.2–31.7 kJ/mol) are also attractive. BLPs do not, however, appear to exhibit significant methane storage capacities (1.9–15.2 mg/g at 273 K with Q st: 17.1–21.7 kJ/mol). Accordingly, CO2/CH4 selectivity studies were performed using the ideal adsorbed solution theory and further supported by initial slope calculations. The results indicate that BLP-1(Br) and BLP-2(Br) exhibit very high CO2/CH4 selectivities 23 and 26, respectively, which make them attractive for small gas separation applications.