Urea-Predoped, KOH-Activated, Corn Stover-Derived Carbon for CO₂ Adsorption

The rising concentration of greenhouse gases causes severe global warming, creating an urgent need for efficient and low-cost carbon dioxide (CO₂) adsorption technologies. Corn stover is an abundant agricultural waste that is often underutilized, leading to resource waste and environmental pollution. To develop value-added utilization of this material, corn stover-derived activated carbon is prepared via urea predoping and controlled potassium hydroxide (KOH) etching, while the effects of pyrolysis temperature, urea doping ratio, KOH dosage, and activation temperature are investigated. Under pure CO₂ at 25°C, the optimal adsorbent exhibits an equilibrium CO₂ adsorption capacity of 3.57 mmol·g^-1. Under pure CO₂ at 0°C, the equilibrium capacity increases to 5.91 mmol·g^-1, indicating that lower temperature favors CO₂ physical adsorption. Under a typical flue gas composition of 20% CO₂/80% N₂ at 25°C, the adsorbent achieves a CO₂ uptake of 1.78 mmol·g^-1 after 50 min. The adsorbent exhibits an ideal adsorbed solution theory CO₂/N₂ selectivity of 30.92. The isosteric heat of adsorption ranges from 28.42 to 23.75 kJ·mol^-1. These values suggest predominantly physical adsorption on heterogeneous sites associated with nitrogen functionalities and structural defects. This study offers insights into the design of biomass-derived CO₂ adsorbents based on corn stover.