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

• Published in: Journal of materials chemistry. A, Materials for energy and sustainability Vol. 7; no. 30; pp. 17842 - 17853
• Main Authors: Shi-Chao, Qi, Ju-Kang, Wu, Lu, Jie, Guo-Xing, Yu, Rong-Rong Zhu, Liu, Yu, Xiao-Qin, Liu, Lin-Bing, Sun
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 2019
• Subjects: Adsorbents; Adsorption; Adsorptivity; Carbon dioxide; Carbon sequestration; composite polymers; Copolymers; Electrostatic properties; Linear functions; Organic chemistry; Quantum chemistry; quantum mechanics
• DOI: 10.1039/c9ta04785a
• ISSN: 2050-7488; 2050-7496

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.