Nitrogen-doped porous carbon through K2CO3-activated bamboo shoot shell for an efficient CO2 adsorption

Abstract

In this paper, a two-stage approach was employed to produce nitrogen-doped porous carbons from bamboo shoot shells. These shells were utilized as a cost-effective biomass resource for the production of activated carbon in gas adsorption. The initial step involved co-carbonization of the bamboo shoot shells with urea, followed by activation using potassium carbonate. A series of nitrogen-doped biochar was prepared by varying the activation temperature and activator ratio. This approach allowed for the investigation of their potential in capturing CO2. Surface analyses were conducted using BET, SEM, and TEM techniques to examine the structural evolution of nitrogen-doped biochar. The results revealed that the fibrous structure of the bamboo shoot shells was well-preserved after carbonization and nitrogen doping, while activation resulted in the formation of a distinct worm-like microporous structure. Among them, the sample BNC-800-2 possessed the largest specific surface area of 1985 m2/g. Notably, the nitrogen-doped biochar activated at 800 °C exhibited remarkable capacity for adsorbing carbon dioxide, with values of 7.52 mmol/g and 3.60 mmol/g at 1 bar and temperatures of 0 °C and 25 °C, respectively. The adsorbent also demonstrated excellent cyclic stability and selectivity for gas mixture (CO2 and N2), attributed to its large specific surface area and narrow pore size, which synergistically contributed to its performance. Furthermore, the adsorption equilibrium was analyzed using the Langmuir and Freundlich isotherm models, with the experimental data showing significant agreement with the Freundlich isotherm model. Additionally, thermodynamic calculations confirmed that the adsorption process of CO2 on nitrogen-doped biochar was spontaneous and exothermic, indicating physical adsorption. This further validates the efficacy of the adsorbent in capturing CO2. This study demonstrates the potential of bamboo shoot shells as a low-cost biomass resource for producing effective adsorbents for CO2 capture.