Oxygen-Functionalized Mesoporous Activated Carbons Derived from Casein and Their Superior CO2 Adsorption Capacity at Both Low- and High-Pressure Regimes

We report on a simple approach for converting casein into oxygen-functionalized mesoporous carbons (MPCs) with extremely high surface areas and carbon contents (∼94%). The materials synthesized by KOH activation of a casein-based nonporous carbon precursor at a carbonization temperature of 800 °C displayed mixed micro- and mesoporosity, which can be easily controlled by simple adjustment of the amount of KOH. The optimized material MPC3, which was prepared with a KOH/carbon source ratio of 3, exhibited a highest specific surface area of 3617 m2 g–1, a pore volume of 2.16 cm3 g–1, and a pore diameter of 2.7–3.1 nm. Because of these excellent textural features, MPC3 achieved excellent CO2 uptake at 1 bar/0 °C (4.12 mmol g–1) and 30 bar/0 °C (39.1 mmol g–1), which are higher than those of mesoporous carbons and silica, activated carbon, carbon nitrides, and carbon nanotubes. The high performance is linked with the combination of excellent textural parameters and unique oxygen functionalities on the surface. It is also demonstrated that these materials are highly stable and can be used repeatedly without much loss of the adsorption capacity. Therefore, the presented materials can be good candidates for pre- and postcombustion CO2 capture.