Effect of metal oxides modification on CO₂ adsorption performance over mesoporous carbon

Porous carbon materials have been modified by various metal oxides (CeO₂, CuO, NiO and Mn₃O₄) with different weight loadings (10–30%). The obtained composite materials were characterized by scanning electron microscope (SEM), N₂ adsorption isotherms, X-ray diffraction (XRD) and thermogravimetric analysis (TGA), and investigated as sorbents for selective capture and removal of carbon dioxide. The overall CO₂ adsorption capacity of AMC decreases upon metal oxides modification due to the reduction in the total surface area of the composite. Interestingly, CO₂ adsorption capacity of AMC at relative low pressure range (below 0.4 bar) is increased with high metal oxides loading (30%), especially for NiO modified AMC. This is explained by the increased interaction strength between CO₂ and the metal oxides than with the carbon surface. The CO₂/N₂ selectivity values of the AMC modified with metal oxides are generally higher than the parent AMC, with the 30% NiO-modified AMC showing 72% increase in the selectivity. This enhancement in selectivity is attributed to an increased interaction between CO₂ and the introduced metal oxides, which is supported by the increased isosteric heats of adsorption of CO₂ after metal oxides modification. The results presented here demonstrate that the adsorption properties including capacity and selectivity of carbon materials are influenced by both their textural characteristics (such as surface area and pore volume) and the surface chemistry, which can be affected by the type and concentration of introduced metal oxides.