Synthesis and characterisation of K₂CO₃-activated carbon produced from distilled spent grains for the adsorption of CO₂

Activated carbon was prepared from distilled spent grains (DSG) using K₂CO₃ activation and chitosan modification. The effects of activator dosage, activation temperature, and the incorporation of chitosan as a nitrogen source on the adsorption performance were studied in this paper. The activated carbons were characterised by scanning electron microscopy, X-ray photoelectron spectroscopy, and nitrogen and carbon dioxide gas adsorption. Under the optimal conditions, the BET-specific surface area, total pore volume, and microporous volume of the activated carbon were as high as 1142 m²/g, 0.62 cm³/g, and 0.40 cm³/g, respectively. Chitosan was used as the nitrogen source, and surface modification was carried out concurrently with the K₂CO₃ activation process. The results revealed a carbon dioxide adsorption capacity of 5.2 mmol/g at 273.15 K and 1 bar without a nitrogen source, which increased to 5.76 mmol/g after chitosan modification. The isosteric heat of adsorption of CO₂ all exceed 20 kJ/mol, hinting at the coexistence of both physisorption and chemisorption. The adsorption behaviour of the DSG-based activated carbon can be well-described by the Freundlich model.