NaNO2-loaded mesoporous MgO for high-efficiency CO2 capture: Synthesis, characterization and novel mechanistic insights

The development of efficient CO 2 adsorbents is critical for achieving net-zero targets. MgO represents a promising solid adsorbent for CO 2 capture, yet its limited specific surface area and insufficient active sites restrict its adsorption capacity under moderate temperature conditions. A rod-like anhydrous MgCO 3 precursor was hydrothermally synthesized and calcined at 500 °C for 3 h to obtain porous MgO (184.9 m 2 ·g −1 , 0.38 cm 3 /g), which was then modified with 20% NaNO 2 (by mole) via impregnation. This adsorbent achieved an adsorption capacity of 12.6 mmol g −1 after 120 min under a pure CO 2 atmosphere at 325 °C. Comprehensive characterization reveals that NaNO 2 modification leads to the NaNO 3 and Na 2 CO 3 formation on the MgO surface during calcination. The introduced NaNO 3 effectively promotes oxygen vacancy formation, while the generated Na 2 CO 3 serves as heterogeneous nucleation sites, collectively reducing the reaction energy barrier and enhancing interfacial mass transfer. This synergistic effect facilitates the MgCO 3 formation followed by its conversion to the thermodynamically more stable Na 2 Mg(CO 3 ) 2 . Kinetic studies elucidate that adsorption is dominated by surface chemical reactions and diffusion mechanisms at different stages. These fundamental insights into the adsorption mechanisms of nitrite-modified MgO provide valuable guidance for the rational design of advanced MgO-based CO 2 adsorbents with enhanced performance.