Modification of activated carbon with nitrogen-based deep eutectic solvents for enhanced CO₂ adsorption

In the past few decades, carbon dioxide (CO₂) concentration in the atmosphere has become a major concern. This research study focused on CO₂ adsorption using coconut shells’ activated carbon (AC), modified with deep eutectic solvents (DESs) to improve AC’s adsorption efficiency. Nitrogen-based DESs: choline chloride (ChCl):urea (ACDES1), ChCl:polyethylenimines (PEI) (ACDES2), and ChCl:urea:PEI (ACDES3) with different impregnation ratios were investigated. The CO₂ adsorption test was performed in a packed-bed adsorption column at constant temperature (30 °C) with initial CO₂ concentration and flow rate of 15% and 200 mL/min, respectively. Among the adsorbents investigated, ACDES1 of impregnation ratio 1:2 exhibited the highest adsorption capacity (21.41 mg/g) and the longest breakthrough (18.1 min) and saturation times (23.7 min). Despite the reduction in the specific surface area and pore volume during impregnation, determined through Brunauer–Emmett–Teller (BET) analysis, DES functionalization introduced active sites that promoted chemisorption and enhanced CO₂ adsorption. Additionally, ACDES1 showed good recyclability with less than 5% reduction in CO₂ adsorption capacity over five cycles. Besides, ACDES1 also showed high thermal stability, collectively suggesting the potential of the ChCl-urea-impregnated AC for CO₂ capture in the industries.