Taguchi L9 (34) orthogonal array study based on methylene blue removal by single-walled carbon nanotubes-amine: Adsorption optimization using the experimental design method, kinetics, equilibrium and thermodynamics

Taguchi orthogonal array (L-9 OA) experimental design was used to determine the optimum conditions for the removal of methylene blue (MB) dye using single-walled carbon nanotubes functionalized with an amine group (SWCNT-NH2). The effects of the experimental parameters (MB initial concentration, SWCNT-NH2 dosage, temperature and pH) on the removal efficiency were studied and optimized in terms of the standard average (SA) and signal-to-noise ratio (S/N) in order to efficiently improve the process. Results showed that the initial concentration has the most significant impact on the adsorption of MB onto SWCNT-NH2 and the best conditions were measured to be 20 mg/L initial MB concentration, 0.05 g SWCNT-NH2 dosage, pH 9 and 50 degrees C Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques were used to characterize the adsorbed surface before and after adsorption. Adsorption kinetics of SWCNT-NH2 was studied and modelled using the pseudo-first-order, pseudo-second-order and intraparticle diffusion models and it was best adjusted to the pseudo-second-order model. Moreover, Langmuir isotherm model with regression coefficient R-2 of 0.9479, was the best fit for the equilibrium adsorption study and the adsorption capacity was found to be 13.62 mg g(-1). The thermodynamic study showed that the adsorption of MB dye is spontaneous and endothermic. (C) 2019 Elsevier B.V. All rights reserved.