Pore-Hierarchy Engineering of Cigarette Butt Waste Into Porous Carbon for CO₂ Adsorption

Cigarette butts are a persistent plastic-rich waste stream commonly disposed of in landfill, creating environmental and resource-recovery challenges. Their cellulose-acetate-rich filters and organic components, however, provide a potential precursor for waste-derived porous carbons. Here, whole cigarette-butt (WCB) waste was converted into hierarchical porous carbons by carbonization followed by Na₂CO₃ activation. The pore structure was tuned from poorly developed porosity to a micro-mesoporous network whose development varied with Na₂CO₃ loading. Pore development increased across the WCB-x series up to 83 wt.% Na₂CO₃, beyond which over-activation reduced the effective adsorption network. WCB-83, the highest-uptake sample within the Na₂CO₃ series, combined a specific surface area of 750 m² g^{- 1} with the micropore volume of 0.24 cm³ g^{- 1}, delivering 3.0 mmol g^{- 1} CO₂ at 273 K and 1 bar. This exceeded both over-activated WCB-91 (2.6 mmol g^{- 1}) and the NaOH-activated counterpart WCB-OH-83 (1.2 mmol g^{- 1}). At 298 K, WCB-83 adsorbed 0.3 mmol g^{- 1} CO₂ at 0.15 bar and 1.0 mmol g^{- 1} at 1 bar. Temperature-dependent adsorption gave apparent isosteric heats of approximately 53 to 59 kJ mol^{- 1}, while Ideal Adsorbed Solution Theory (IAST) -predicted CO₂/N₂ selectivity reached 120. This work demonstrates a waste-valorization strategy for converting cigarette-butt waste into CO₂-selective hierarchical carbon adsorbents.