Nitrogen-doped activated carbon from palmyrah kernel shell biomass for efficient CO₂ capture

Anthropogenic carbon dioxide (CO₂) emissions, primarily from fossil fuel combustion and industrial growth, have significantly contributed to global warming and climate change. This study reports the development of nitrogen-doped activated carbon material, derived from palmyrah kernel shell (PKS), as an adsorbent for CO₂ capture. It was synthesized in a two-step process: melamine as a nitrogen source at varying melamine-to-biomass ratios, followed by chemical activation with KOH. The prepared materials were then characterized by CHNS, FTIR, BET, XPS, SEM-EDX, and TGA to investigate their elemental composition, functional groups, porosity, chemical states, surface morphology, elemental distribution, and thermal stability. The adsorption-desorption behavior was analyzed using a thermo-gravimetric weighing method, while volumetric measurements were performed to further evaluate the pressure-dependent CO₂ capture performance. The nitrogen doping is effected by varying the ratio of PKS biomass to melamine. XPS N1s deconvolution confirmed the presence of pyridinic, pyrrolic, and graphitic nitrogen configurations, while SEM-EDX mapping showed their relatively uniform elemental distribution throughout the carbon matrix. The material with a 3:1 ratio exhibited excellent CO₂ adsorption performance of 174.3  ${mgg}^{-1}$ at 25 °C and 242.9  ${mgg}^{-1}$  at 0 °C under ambient pressure, with corresponding desorption of 174.6  ${mgg}^{-1}$  at 25 °C and 242.6  ${mgg}^{-1}$ at 0 °C, respectively. Adsorption kinetics were evaluated using the pseudo-second-order model, and thermodynamic parameters were determined to assess the temperature-dependent adsorption. Results showed that the 3:1 N-doped activated carbon derived from PKS exhibited the highest CO₂ uptake and strong CO₂/N₂ selectivity. Further, the adsorption-desorption cycles establish material stability beyond 20 cycles. Our findings reveal that the lower the nitrogen content, the more efficient the CO₂ capture. The carbonaceous material thus derived from waste biomass enables carbon-based carbon capture, further reducing the carbon footprint of the capture process.