A Two Step Postsynthetic Modification Strategy: Appending Short Chain Polyamines to Zn-NH₂-BDC MOF for Enhanced CO₂ Adsorption

Functionalizing metal-organic frameworks (MOFs) with amines is a commonly used strategy to enhance their performance in CO2 capture applications. As such, this work, two-step covalently functionalize NH2-containing MOFs short chain polyamines was developed. In the first step, parent MOF, Zn4O(NH2-BDC)3, exposed bromoacetyl bromide (BrAcBr), which readily reacts pendant -NH2 groups on 2-amino-1,4-benzenedicarboxylate (NH2-BDC2-) ligand. 1H NMR of digested MOF sample revealed that as much 90% ligands could be functionalized step. Next, samples 60% acetyl bromide, Zn4O(NH2-BDC)1.2(BrAcNH-BDC)1.8, several including ethylenediamine (ED), diethylenetriamine (DETA), and tris(2-aminoethyl)amine (TAEA). Subsequent analysis indicated total 30%, 28%, 19% were successfully grafted ED, DETA, TAEA, respectively. adsorption properties amine studied. The best performing material, TAEA-appended-Zn4O(NH2-BDC)1.2(BrAcNH-BDC)1.8, exhibits zero-coverage isosteric heat -62.5 kJ/mol, value considerably higher than one observed for framework, -21 kJ/mol. Although boosted affinity only leads slight increase capacity low-pressure regime (0.15 bar), interest postcombustion carbon dioxide capture, CO2/N2 (15/85) selectivity at 313 K 143, ∼35 times 4.1. Such enhancements are attributed accessible primary amines, This hypothesis further supported via situ DRIFTS measurements TAEA-Ac-Zn4O(NH2-BDC)1.2(BrAcNH-BDC)1.8 after exposure CO2, chemisorption formation hydrogen bonded carbamates/carbamic acid CO2δ- species; latter adducts formed between [amineH]+Br- salts produced during grafting