Polarization of CO2 for improved CO2 adsorption by MgO and Mg(OH)2

• Published in: Applied surface science 2021-10, Vol.562, p.150187, Article 150187
• Main Authors: Wu, Shunnian, Tan, Boon Teoh, Senevirathna, Hasanthi L., Wu, Ping
• Format: Article
• Language: English
• Subjects: Adsorption energy; CO2 adsorption; First principles calculations; Polarization; Thermogravimetric analysis
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/j.apsusc.2021.150187

[Display omitted] •Weak chemical adsorption of CO2 molecule on MgO surface is significantly increased by the presence of H2O.•Defects formed by dehydration dramatically improved CO2 adsorption on Mg(OH)2 surface with formation of carbonate-like structure.•The electrospun MgO/Mg(OH)2 composite shows substantially increased CO2 adsorption capacity and faster kinetics than pure MgO.•Three CO2 polarization mechanisms are disclosed to improve CO2 adsorption, i.e. electron transfer to CO2, electron localization within CO2, and uneven electron distribution in two O atoms of CO2. Low cost MgO has an attractive theoretical CO2 capture capacity of 1090 mg/g when it is in equilibrium with MgCO3, but only ~ 1–10% of this predicted absorption limit is realized experimentally. Changes in structure that dominate the experimental carbon capture process remain unclear. Here, we simulate the CO2 adsorption on comparative MgO and Mg(OH)2 surfaces, using a combined theory and experimental approach. Subsequently, the role of H2O molecules to carbon adsorption on MgO and Mg(OH) surfaces, as well as the effect of dehydration defect in Mg(OH)2, were investigated via DFT calculations. We found (1) H2O molecules significantly facilitate CO2 capture on MgO but not on Mg(OH)2, (2) formation of dehydration defects on Mg(OH)2 dramatically increases the CO2 absorption energy from −0.045 eV to −1.647 eV, (3) three electronic mechanisms, i.e., electron transfer to CO2, electron localization within CO2, and uneven electron distribution in two O atoms of CO2, were identified that are responsible for the calculated increase in CO2 adsorption energy. These results enable a novel design of composite MgO/Mg(OH)2 adsorbents that controls the formation of dehydration defects, consequently, offering exciting possibilities in carbon capture, utilisation and storage (CCUS) applications and room temperature carbon mineralization.