Magnesium oxide-modified nanographene hybrid nanostructures engineered by green synthesis method using hemp stalk bio-extract for CO₂ capture

This study comprehensively investigates the CO₂ adsorption performance of MgO-modified nanographene (NG-MgO/green) hybrid nanostructures, which were obtained for the first time using a green synthesis method with hemp stalk bio-extract, with the aim of contributing to sustainable carbon capture technologies. The integration of MgO into the NG surface has increased the surface basicity and facilitated strong Lewis basic interactions with CO₂. The natural reducing and stabilizing components in the bio-extract (e.g., polyphenols and flavonoids) have facilitated the conversion of Mg²⁺ ions into MgO and contributed to the homogeneous dispersion of the particles. SEM and TEM analyses revealed that MgO nanoparticles were homogeneously and densely bound to the NG surface without clustering. BET analyses showed that the NG-MgO/green has a surface area of 672 m²/g, a total pore volume of 0.32 cm³/g, and an average pore diameter of 4.45 nm. This micro/mesoporous structure facilitated the efficient diffusion and adsorption of CO₂ molecules. In CO₂ adsorption tests conducted at 298 K and 273 K, the NG-MgO/green exhibited uptake capacities of 4.35 mmol/g and 5.05 mmol/g, respectively. Analysis of the adsorption isotherm models revealed that the Langmuir model provided the best fit to the experimental data for all the nanostructures, with R² values above 0.99. The isosteric heat of adsorption (Q_st) values were calculated to be between 16.5 and 22.1 kJ/mol, indicating that physical interactions are dominant. The reuse efficiency reaching 96 % after five consecutive adsorption-desorption cycles demonstrates the thermal and structural durability of the NG-MgO/green. The results obtained demonstrate that the NG-MgO/green is a promising CO₂ adsorbent in terms of both environmental sustainability and technical performance.