Structure-performance relationships of magnesium-based CO2 adsorbents prepared with different methods

Magnesium-based adsorbents present great potential in separating CO 2 from flue gas stream. To satisfy the requirement of efficient CO 2 capture, it is imperative to select suitable methods for preparing MgO adsorbents with good physicochemical properties. In this study, MgO adsorbents were prepared with different methods using MgCl 2 ·6H 2 O as magnesium precursor, and the effect of synthesis method on their structure-performance relationships were investigated. It is found that MgO adsorbents prepared with different methods exhibited varied physicochemical properties, and these were associated with their diverse CO 2 adsorption capacities. Amongst the different MgO adsorbents, the sample prepared with the solid-state chemical reaction method (MgO-SR) featured good textural properties (high specific surface area and total pore volume of 100.03 m 2 /g and 0.67 cm 3 /g), preferable surface morphology (sheet-like structure with reduced layer diffusion resistance) and excellent CO 2 adsorption capacity (2.39 mmol CO 2 /g). The solid-state chemical reaction method endowed the adsorbent with abundant surface basic active sites, and CO 2 molecules interacted with the weak sites (OH group), medium sites (Mg-O pairs) and strong sites (O 2− ) to form stable bicarbonate, bidentate and unidentate carbonates. The experimental CO 2 uptakes were in good agreement with the values predicted by the Avrami fractional kinetic model. Physical adsorption and chemisorption coexisted in the CO 2 adsorption process and the chemisorption sites played a dominant role. The approach enlightens the facile fabrication of cost-effective MgO adsorbents from waste precursors for large-scale CO 2 capture applications.