Surface Modification of Activated Carbon by Nitrogen Doping and KOH Activation for Enhanced Carbon Dioxide Adsorption Performance

Nitrogen-doped activated carbon (N-AC) was successfully prepared by KOH-activation and nitrogen doping using ammonia (NH3) heat treatment. Coconut shell-derived activated carbon (AC) was heat-treated under NH3 gas in the temperature range of 700°C–900°C. Likewise, the mixture of potassium hydroxide (KOH) and AC was heated at 800°C, followed by heat treatment under NH3 gas at 800°C (hereafter referred to as KOH-N-AC800). Scanning electron microscopy (SEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and Brunauer-Emmett-Teller (BET) method were utilized to analyze morphology, crystallinity, chemical bonding, chemical composition and surface area. The surface area and porosity of N-AC increased with increasing NH3 heat treatment. Similarly, the nitrogen content in the N-AC increased from 3.23% to 4.84 at% when the NH3 heat treatment was raised from 700°C to 800°C. However, the nitrogen content of N-AC decreased to 3.40 at% after using NH3 heat treatment at 900°C. The nitrogen content of KOH-N-AC800 is 5.43 at%. KOH-N-AC800 and N-AC800 exhibited improvements of 33.66% and 26.24%, respectively, in CO2 adsorption compared with AC. The enhancement of CO2 adsorption of KOH-N-AC800 is attributed to the synergic effect of the nitrogen doping, high surface area, and porosity. The results exhibited that nitrogen sites on the surface play a more significant role in CO2 adsorption than surface area and porosity. This work proposes the potential synergistic effect of KOH-activation and nitrogen doping for enhancing the CO2 adsorption capacity of activated carbon.