Disclosed is a novel adsorbent having excellent adsorption durability and high adsorption efficiency while having improved durability, thereby improving a carbon dioxide (CO2) separation process. A mesoporous cellular foam impregnated with an iron (Fe)-substituted heteropolyacid includes a mesoporous cellular foam support and an Fe-substituted heteropolyacid, and the mesoporous cellular foam impregnated with an Fe-substituted heteropolyacid has superior CO2 adsorption performance and exhibits excellent reproduction performance even after CO2 adsorption and desorption are performed several times through temperature changes, thereby enabling efficient and economical CO2 separation.