Reactivity of azole anions with CO₂ from the DFT perspective

Azole anions are key components in CO₂ capture materials that include ionic liquids and porous solids. Herein, we use density functional theory (DFT) and a Langmuir-type adsorption model to study azole anion-CO ₂ interactions. Linear CO₂ has to be bent by approximately 45° to form an N-C bond within the azole ring. The energy cost of bending renders CO₂ absorption much more difficult compared to SO₂ absorption. For different azole anions, the number of nitrogen atoms in the ring and the natural bond orbital energy of the reacting nitrogen lone pair, both linearly correlate with the calculated reaction enthalpy and are useful handles for new sorbent designs. Unlike for SO₂, the azole parent architecture (unsubstituted) does not allow successive CO₂ absorption under mild conditions (<0.12 MPa and at room temperature). Experimental CO₂ and SO₂ absorption isotherms are reproduced by using the Langmuir model parameterized with the calibrated DFT reaction enthalpies. This study provides insight for designing azole-based CO₂-capture materials. Catch me if you can: Azole anions represent a key component in CO₂ absorption materials. A variety of different azole anions have been investigated for their reactivity with CO₂ by using DFT calculations and a Langmuir adsorption model. Unlike SO₂, multi-site CO₂ absorption does not occur for azole anions under normal conditions. This study provides insight into designing azole-based CO ₂-capture materials.