N, S Co-doped porous carbons from coconut shell for selective CO2 adsorption

Abstract

The CO₂ capture from flue gas using biomass-derived porous carbons offers a promising and sustainable approach to mitigate greenhouse gas emissions. However, achieving high adsorption performance under ambient conditions requires synergistic optimization of pore architecture and surface chemistry. In the present work, a facile and scalable synthesis method was developed to prepare nitrogen and sulfur co-doped porous carbons using coconut shell as a renewable carbon precursor and thiourea as a dual heteroatom source. Chemical activation with KOH was employed to tune the porosity and surface functionality. The optimal adsorbent exhibited a high BET surface area (1315 m²/g), large narrow micropore volume (0.66 cm³/g), and significant heteroatom content (3.39 at.% N and 0.39 at.% S), resulting in superior CO₂ uptake of 4.38 and 6.46 mmol/g at 25 °C and 0 °C, 1 bar, respectively. Additionally, as-prepared adsorbents demonstrated high CO₂/N₂ selectivity, rapid adsorption kinetics, moderate isosteric heat of adsorption, and excellent cycling stability over five adsorption–desorption cycles. These findings underscore the dual role of narrow micropores and heteroatom-rich functional groups in enhancing gas–solid interactions and provide a green and effective strategy for designing high-efficiency CO₂ sorbents from coconut shell waste.