Enhanced adsorption of cationic and anionic dyes using cigarette butt-based adsorbents: Insights into mechanism, kinetics, isotherms, and thermodynamics

The present study provides an eco-friendly and economical way to recycle discarded cigarette butts (CBs). The raw CBs were treated with NaOH (CB-B) and integrated with chitosan (Cs), and further applied as an adsorbent for the removal of synthetic dyes. Two common cationic dyes of methylene blue (MB) and crystal violet (CV) and one anionic dye of reactive blue 19 (RB 19) were selected as model adsorbates. The study results revealed that CB-B showed a high adsorption ability toward cationic dyes, while the CB-B/Cs composite exhibited a stronger affinity for the anionic RB 19. The adsorption of all selected dyes onto CB-B and CB-B/Cs was a spontaneous exothermic process, conforming to the pseudo-first-order kinetic and Langmuir isotherm models. The maximum adsorption capacities for MB, CV and RB 19 at pH of 7, an adsorbent dosage of 4, and a temperature of 25 °C were 89.85, 82.41, and 304.49 mg/g, respectively. The primary adsorption mechanism was physical adsorption with the participation of electrostatic attraction. The CB-based adsorbents displayed high reusability, maintaining more than 75% after four consecutive cycles of reuse. This study demonstrates the promising application potential of CB-based adsorbents for treating synthetic dyes in wastewater. The conversion of CBs into a useful high-value material has special significance for environmental engineering.