CO 2 direct air capture in early hydration stage for light-burned MgO: low-dimensional agglomeration regime

Abstract

The rise in atmospheric carbon dioxide (CO 2 ) concentrations has necessitated the development of costeffective and environmentally friendly sorbent materials for the direct air capture (DAC) of CO 2 . In this study, CO 2 adsorption via DAC during early hydration stages is investigated for light-burned magnesium oxide (MgO) with open-structured grain boundaries. Isolated monodentate carbonates MgCO 3 are formed during DAC on the O sites on the interior surfaces of grain boundaries immediately after contact with air.Upon hydration, atmospheric CO 2 preferentially adsorbs on another O site as a MgCO 3 hydrate to meet the hydrogen-bond environment with the former O site. DAC-originated MgCO 3 hydrates are thus able to be stabilized on grain-boundary surfaces, exhibiting excellent DAC performance with a CO 2 adsorption capacity and rate of ~0.7 mol/kg and ~0.1 mol/kg/h, respectively. A reasonable molecular model is presented for low-dimensionally agglomerated MgCO 3 hydrates constrained on grain-boundary surfaces, which enhances their thermal stability.