Defect-mediated CO2 activation at two-dimensional MgO monolayers: A DFT study

CO2 capture is vital to address fossil fuel depletion and to mitigate climate change by reducing the emission of greenhouse gases and fostering the sustainable generation and use of energy. Through first-principles calculations based on the density functional theory (DFT), in this work we report the CO2 adsorption characteristics at graphene-like pristine and defect-containing 2-dimensional MgO monolayers via a detailed investigation of the electronic and geometrical changes. Mono-vacancy, di-vacancy (O and Mg atoms vacancies), and anti-site defects (MgO-A) are studied and our results show chemisorption of the CO2 molecule at 2D MgO with an adsorption energy of −0.79 eV and bending of its linear geometry. Introducing O and Mg vacancies leads to an increase of about 80 % and 178 %, respectively, in these adsorption energies. The anti-site defect MgO-AMg (O atom replaced by Mg atom) was found to be thermodynamically unfavorable, as indicated by a calculated positive defect formation energy, while all other defects exhibit negative formation energies. In the present work, we found that activation of the CO2 molecule occurs at all considered MgO sheets. Engineered atomic defects increase this process, with a maximum adsorption energy of −3.97 eV at the MgO-Mg/O sheet, containing both Mg and O atom vacancies. The defect creation and interaction between the 2D MgO monolayer and CO2 molecule alters the distribution of atomic orbitals as confirmed through projected density of states (PDOS), which is indicative of CO2 activation on these MgO 2d sheets.