Preparation of molten salt promoted MgO for efficient CO2 capture by microwave method: Performance evaluation and mechanism exploration

[Display omitted] •MgO prepared by microwave has small size (6.20 nm) and good adsorption capacity.•20 mol% NaNO3 doping improves the CO2 adsorption performance of MgO (11.9 mmol·g−1).•Increasing O2– sites is helpful for improving performance of MgO-based CO2 adsorbent.•CO2 adsorption can divide into co-adsorption, chemical reaction and diffusion. MgO’s great potential for capturing CO2 has drawn a lot of attention, but the limited O2– sites prevents its further development. This work proposed a microwave-induced method (microwave hydrothermal and microwave sintering) to produce high-performance MgO CO2 adsorbent and was further modified using carbonates (K2CO3) and nitrates of alkali metals (NaNO3, KNO3). The outcomes demonstrated that the small particle size MgO nanocrystals (6.20 nm) with a CO2 uptake of 1.8 mmol·g−1 could be produced by a unique method of microwave heating from the inside out. Among the modified samples, addition of 20 mol% NaNO3 on the surface of MgO exhibited the highest CO2 uptake (11.91 mmol·g−1), and the uptake was still 7.9 mmol·g−1 after 10 cycles. The addition of molten salt changed the adsorbent’s active sites, resulting in an increase in O2– alkaline sites and the activation of MgO lattice defects, both of which improved the sample’s CO2 adsorption performance. This work could offer a new idea for creating affordable and effective CO2 solid adsorbents to capture CO2.