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.