Underlying mechanism of CO₂ adsorption onto conjugated azacyclo-copolymers: N-doped adsorbents capture CO₂ chiefly through acid-base interaction?

The empiricism that extrinsic or doped materials universally perform much better than their intrinsic counterparts has been verified to be feasible in the adsorptive CO₂ capture. Thus, a variety of N-doped solid adsorbents are well-engineered to adsorb CO₂. However, the true nature of the N-doped sites in the aggregation state and the underlying mechanism of CO₂ adsorption therein are difficult to determine. In the present study, four well-defined azacyclo copolymers with peculiar textural characteristics, uniformly arrays and tunably effective N-doped sites were fabricated to experimentally determine the precise relation between adsorbed CO₂ molecules and the N-doped sites incorporated into an adsorbent. With multifaceted quantum chemical computations, induction forces were proven to account for the improved CO₂ adsorption on the N-doped sites instead of the conventionally assumed generalized acid-base interaction. The negative electrostatic potentials were demonstrated to be the real cause for improving the CO₂ adsorption and a robust indicator for the effectiveness of the N-doped sites. Besides, a precise linear function is proposed to quantitatively describe this subject-object relationship for the first time.