Valorizing used cigarette filters into porous carbons by sustainable K2CO3 activation for cationic dyes adsorption

Achieving simultaneous ultrahigh capacity and ultrafast kinetics in dye adsorption remains a major challenge. In this paper, used cigarette filters were valorized into porous carbons by a sustainable K2CO3 activation technology under optimized conditions (800 °C, 2 h, 15 wt% K₂CO₃ concentration), and the prepared CPCK-800 was employed for the adsorption of cationic dyes in this paper. This material possesses a substantial specific surface area of 1472.1 m2/g and a pore volume of 0.770 cm3/g. Its 3D honeycomb-like porous architecture, coupled with abundant oxygen-containing groups (with oxygen content as high as 22.29 wt%), facilitates superior adsorption for three typical cationic dyes. The recorded capacities reach 1648.7 mg/g for Methylene Blue (MB), 3431.4 mg/g for both Rhodamine B (RhB) and Malachite Green (MG), which significantly surpass some “super” biochars with complex modifications or activation treatments reported in recent years. Remarkably, 99.8% adsorption efficiency was achieved in only 10 min at 100 mg/L, while a high capacity of 1227.2 mg/g was recorded within just 5 min at 400 mg/L. These quantitative kinetic data, combined with the record-high capacities, demonstrate that CPCK-800 holds significant promise for meeting the stringent residence-time and capacity requirements of practical high-concentration dye wastewater treatment. Studies on the mechanism show that both chemical and physical interactions contribute synergistically to MB adsorption on CPCK-800, such as pore filling, hydrogen bonding, electrostatic attraction, π-π, and n-π interactions. In summary, owing to exceptional anti-interference properties, regenerability and versatility, the CPCK-800 shows great promise as an adsorbent for real dye wastewater treatment.