Solvent-free conversion of cucumber peels to N-doped microporous carbons for efficient CO₂ capture performance

For the first time, cucumber peel (CP) biomass was used to produce a novel three-dimensional (3D) carbon precursor using simple pyrolysis. The carbon precursor was then converted into a series of N-doped microporous carbons using a facile solvent-free process involving a chemical agent and melamine. A solvent-free process is an effective approach because it does not require hazardous solvents, several complex steps, and high costs. The optimized sample (CP–K-900) has a high CO₂ adsorption capacity (7.3 mmol g⁻¹ at 273 K and 1 bar) because it has (i) excellent textural features (a high specific surface area (SSA) of 2682 m² g⁻¹, large micropore volume of 1.01 cm³ g⁻¹, and high concentration (65.1%) of narrow micropores (<0.7 nm)), high degree of graphitization, and (ii) a feasible concentration of self-doped N and O contents. According to our experimental results, porous textural features is more imperative for high CO₂ uptakes than high N-doping contents. A micropore size of less than 1 nm produced the best-fit linear relationship with CO₂ capture at 273 K. Furthermore, the optimized material has an intermediate isosteric heat of adsorption (46.4 kJ mol⁻¹), indicating the physisorption nature of the adsorption process. The excellent regeneration ability of microporous carbons over six consecutive adsorption-desorption cycles under flue gas conditions (15%CO₂/85%N₂) revealed the potential of as-designed cost-effective and feasible microporous carbonaceous materials for efficient practical environmental remediation applications.