Colloidal Nanoclusters of MgO Coated with Alkali Metal Nitrates/Nitrites for Rapid, High Capacity CO2 Capture at Moderate Temperature

Abstract

Colloidal nanoclusters of metal oxides constitute a promising new class of building blocks for a range of advanced functional materials. Herein, we report on the development of colloidal nanoclusters of MgO for CO₂ capture prepared by a novel nonhydrolytic sol–gel reaction followed by the deposition of alkali metal salts by methanol evaporation-induced surface precipitation. The CO₂ uptake exceeded 11.7 mmol g^–1 (514.8 mg CO₂ per 1 g of adsorbent) in 30 min in the presence of 100% dry CO₂ under ambient pressure (1 bar) at 340 °C and reached 15.7 mmol g^–1 (690.8 mg CO₂ per 1 g of adsorbent) in 4 h. Colloidal nanoclusters possessing multiple inner grain boundaries and rough surfaces allowed for a dramatic increase in active surface area of MgO coated with thin layers of alkali metal salts and enabled the rapid conversion of MgO to MgCO₃ with high conversion ratio. It was also discovered that the CO₂ uptake loading and the regenerability of the sorbents can be enhanced on introduction of nitrite salts to the coating layer through the formation of magnesium nitro or nitrate species, which increased the critical thickness of product layers and mitigated the degradation of nanoclusters over the repeated sorption/desorption cycles.