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

Abstract

Nitrogen-doped activated carbon (N-AC) was successfully prepared by KOH-activation and nitrogen doping using ammonia (NH<inf>3</inf>) heat treatment. Coconut shell-derived activated carbon (AC) was heat-treated under NH<inf>3</inf> gas in the temperature range of 700℃–900℃. Likewise, the mixture of potassium hydroxide (KOH) and AC was heated at 800℃, followed by heat treatment under NH<inf>3</inf> gas at 800℃ (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 NH<inf>3</inf> heat treatment. Similarly, the nitrogen content in the N-AC increased from 3.23% to 4.84 at% when the NH<inf>3</inf> heat treatment was raised from 700℃ to 800℃. However, the nitrogen content of N-AC decreased to 3.40 at% after using NH<inf>3</inf> heat treatment at 900℃. 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 CO<inf>2</inf> adsorption compared with AC. The enhancement of CO<inf>2</inf> 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 CO<inf>2</inf> adsorption than surface area and porosity. This work proposes the potential synergistic effect of KOH-activation and nitrogen doping for enhancing the CO<inf>2</inf> adsorption capacity of activated carbon.