Evaluating the CO2 capture potential of MgO sheets: a DFT study on the effects of vacancy and Ni doping for assessing environmental sustainability

Abstract

Investigations on two-dimensional materials for efficient carbon dioxide (CO₂) capture and storage have recently attracted much attention, especially in the global industrial sector. In this work, the CO₂ uptake by three configurations of two-dimensional magnesium oxide was investigated using density functional theory. CO₂ capture analysis was performed considering the geometrical, thermophysical, vibrational, electronic and optical properties. Results indicated that CO₂ adsorption by magnesium oxide (MgO) sheets is a spontaneous process accompanied by a decrease in Gibbs free energy. Moreover, the CO₂ molecular entropy and enthalpy of the CO₂ adsorbed sheet were decreased, indicating that the entire process was enthalpy-driven. Among the pristine, vacant and nickel-doped (Ni-doped) MgO sheets, the Ni-doped system was found to have the highest values of Gibbs free energy, enthalpy and entropy in the order of −51.366 kJ mol^−1-K, −65.105 kJ mol⁻¹ and 127.606 J mol⁻¹, respectively. It was also found to adsorb CO₂ in the ultraviolet and visible (UV-Vis) regions within the range of 100–850 nm. Electronic interactions demonstrated that metallicity was significantly induced on the MgO sheet Ni impurity states, which enhanced the adsorption ability. Notably, hybrid orbitals between p_y and p_z revealed strong physisorption, as confirmed by the partial density of states (PDOS). The findings of this research promote CO₂ capture sustainability by encouraging future experimentalists to use two-dimensional MgO as a better surface for CO₂ capture.