Adsorption of Acid Blue 92 Dye from Aqueous Solutions by Single-Walled Carbon Nanotubes: Isothermal, Kinetic, and Thermodynamic Studies

Abstract

The aim of this study was to investigate the adsorption of Acid Blue 92 (AB92) dye onto single-walled carbon nanotubes (SWCNTs). The adsorbent was characterised by SEM, TEM, FTIR, and BET. The study comprised batch experiments conducted under varying conditions of dosage (0.01–0.2 g/L), time (10–180 min), pH (3–11), and dye initial concentration (10–200 mg/L). The optimum removal efficiency of 99.4% was achieved for AB92 at an adsorbent dosage of 0.12 g/L, dye initial concentration of 10 mg/L, pH of 3, and contact time of 75 min. The adsorption was best-fit to the pseudo-second order kinetics and Langmuir isotherm models. The monolayer adsorption capacity (qm) was 86.91 mg/g at 333 K. The activation energy of the system was 16.62 kJ/mol. Thermodynamics analysis revealed that the process was spontaneous (∆G0 was between −12.73 and −16.08 kJ/mol) and endothermic (∆H0 = 2.51 kJ/mol). The positive ∆S0 value (0.055 kJ/mol K) also suggests the affinity of the SWCNTs adsorbent for AB92. The mechanism of AB92 dye uptake by SWCNTs was majorly by hydrogen bonds, dipole-induced dipole bonds, London dispersion interactions, π-π acceptor–donor interactions, and the hydrophobic effect. The results reveal that SWCNTs is an effective adsorbent for AB92 removal from industrial effluents and wastewater. • Removal of Acid Blue 92 by single-walled carbon nanotubes (SWCNTs) was examined. • The SWCNTs at dosage of 0.12 g/L removed 99.4% of the dye within 75 min at pH 3. • The pseudo-second order kinetics and Langmuir isotherm equations explained the process.