Adsorption of textile dye in activated carbons prepared from DVD and CD wastes modified with multi-wall carbon nanotubes: Equilibrium isotherms, kinetics and thermodynamic study

Abstract The purpose of the present work was to prepare activated carbon (AC) from low-cost wastes, such as digital versatile discs (DVDs) and compact discs (CDs), coated with carbon nanotubes (CNTs) for adsorption of Acid Orange 7 (AO7) from dye-containing solutions. The surface morphology of the activated carbons from DVDs (DVDsAC), CDs (CDsAC), CNTs, CNTs/DVDsAC and CNTs/CDsAC was determined by XRD and SEM techniques. SEM micrographs of adsorbents clearly show a heterogeneous porous surface with irregular pores in the structure of the activated carbons. Results showed that CNTs/DVDsAC (30.3 mg/g) and CNTs/CDsAC (32.8 mg/g), in comparison with DVDsAC (15.1 mg/g) and CDsAC (9.9 mg/g), were more efficient adsorbents for the adsorption of AO7. The dye adsorption amount (q e ) increases with a reduction in the solution pH, adsorbent dosage and an increase in the initial concentration of AO7 for these two more efficient adsorbents. Pseudo-second order model and Langmuir isotherm fitted with the experimental data. The spontaneous and endothermic processes were analyzed by the thermodynamic studies for the adsorption of AO7. The negative values of ΔG, and the positive values of ΔH and ΔS parameters indicate that the adsorption of AO7 onto CNTs/CDsAC and CNTs/DVDsAC was spontaneous and endothermic, respectively.