Ultrahigh-Capacity Adsorption of Cationic Dyes with Rapid Kinetics Using Used Cigarette Filters-Based Carbons Activated by KHCO3

The development of adsorbents that simultaneously achieve high adsorption capacity and rapid kinetics is critical for treating organic dyes, particularly at high concentrations. Herein, novel used cigarette filter (UCF)-based carbons were synthesized via one-step pyrolysis employing an eco-friendly activator KHCO3. The resulting CPCHK-800 carbon material possesses a high specific surface area of 1533 m2/g and a high volume of 0.716 cm3/g. Benefiting from a three-dimensional (3D) honeycomb architecture of graphene-like nanosheets and abundant oxygen groups (19.98 wt %), CPCHK-800 exhibited high adsorption capacities for MB (1328.7 mg/g), RhB (3129.5 mg/g), and MG (3425.9 mg/g) at an adsorbent dosage of 0.2 g/L. Notably, near-complete removal of MB was achieved within 10 min at 100 mg/L, and an adsorption capacity of 1023.9 mg/g was reached within 5 min at 400 mg/L and 0.2 g/L dosage. Such rapid kinetics highlight its potential for treating high-concentration dye wastewater. The Langmuir model best describes the isotherms (R2 = 0.982, qmax = 1657.4 mg/g) with favorable RL values (0.0049–0.0312). The adsorption process is spontaneous and endothermic. Mechanistic studies reveal that MB adsorption involves synergistic contributions from pore filling, hydrogen bonding, electrostatic attraction, π-π, and n-π interactions. Furthermore, CPCHK-800 maintains 92.2% of its initial adsorption capacity after five cycles, decreasing from 1089.3 to 1004.7 mg/g, and maintains 87.3% of its salt-free performance at 0.5 mol/L NaCl, highlighting its excellent reusability and anti-interference capability. These quantitative results confirm that CPCHK-800 is a promising, cost-effective, and environmentally safe adsorbent for practical high-concentration cationic dye wastewater treatment.