Hierarchical porous composite Mg-MOF-74/MCFs were successfully synthesized using a simple and facile method under in situ solvothermal conditions. Textural structures and morphologies of the composites were characterized by X-ray diffraction (XRD), N₂ adsorption–desorption isotherms, and scanning electron microscopy (SEM), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). The results demonstrate that a large amount of nanosized Mg-MOF-74 particles is incorporated into the pores of mesocellular siliceous foams (MCFs) without remarkable aggregation and the composites possess microporous and mesoporous characteristics of both components. In addition, CO₂ adsorption properties of the composites were tested in a fixed bed with/without hydrothermal treatment. The total CO₂ adsorption capacities were calculated by breakthrough curves. The CO₂ adsorption capacity of the composites reaches 1.68 mmol/g, which is smaller than that of pristine Mg-MOF-74. However, the total CO₂ adsorption capacity of the composites after hydrothermal treatment reaches 2.66 mmol/g, which is larger than that of Mg-MOF-74 (2.39 mmol/g) under the same condition. XRD patterns and SEM images of the composites demonstrate that the hydrothermal stability and CO₂ adsorption performance of the composites were improved compared with those of pristine Mg-MOF-74 after hydrothermal treatment.

The accumulation and incineration of crop waste pollutes the environment and releases a large amount of CO ₂ .

To reduce the cost of CO₂ capture, polyethylene polyamine (PEPA), with a high amino density and relatively low price, was loaded into MCM-41 to prepare solid sorbents for CO₂ capture from flue gases.

To achieve the "double carbon" (carbon peak and carbon neutrality) target, low-cost CO₂ capture at large CO₂ emission points is of great importance, during which the development of low-cost CO₂ sorbents will play a key role. Here, we chose peanut shells (P) from crop waste as the raw material and KOH and K₂CO₃ as activators to prepare porous carbons by a simple one-step activation method. Interestingly, the porous carbon showed a good adsorption capacity of 2.41 mmol/g for 15% CO₂ when the mass ratio of K₂CO₃ to P and the activation time were only 0.5 and 0.5 h, respectively, and the adsorption capacity remained at 98.76% after 10 adsorption-desorption cycle regenerations. The characterization results suggested that the activated peanut shell-based porous carbons were mainly microporous and partly mesoporous, and hydroxyl (O-H), ether (C-O), and pyrrolic nitrogen (N-5) functional groups that promoted CO₂ adsorption were formed during activation. In conclusion, KOH- and K₂CO₃-activated P, especially K₂CO₃-activated P, showed good CO₂ adsorption and regeneration performance. In addition, not only the use of a small amount of the activator but also the raw material of crop waste reduces the sorbent preparation costs and CO₂ capture costs.

The design and development of low-cost sorbents is vital for CO ₂ capture from flue gases.