Magnetic multi-walled carbon nanotubes-loaded alginate for treatment of industrial dye manufacturing effluent: adsorption modelling and process optimisation by central composite face-central design

Abstract

ABSTRACT In the present study, dye(ADMI, American Dye Manufacturers’ Institute) removal from raw textile wastewater was investigated by magnetic multi-walled carbon nanotubes-loaded alginate (CNT-Alg-Fe3O4). The effect of key factors i.e., pH, adsorbent dose and contact time in treatment process was modelled and optimised using response surface methodology-based central composite face-centred design (RSM-CCF). Adsorbents were characterised using Fourier transform infrared (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), vibrating-sample magnetometer (VSM), and energy-dispersive X-ray spectroscopy (EDS).Low value of p (7.9714e-13) and RSD (1.121) parameters, along with coefficient of determination >0.953 implied that the developed model well-fitted with experimental data. Under the optimised conditions, including pH of3, CNT-Alg-Fe3O4 dose of10 g L-1, and contact time of85.55 min, removal efficiency and ADMI adsorption capacity were obtained as 98.43% and 138.97ADMI/g, respectively. Fitting of data with the Langmuir isotherm (R2 = 1, X2 = 0.012) and Pseudo-second-order kinetics (R2 = 0.993, X2 = 0.015) showed that adsorption process is monolayer and chemical in nature. ΔH°> 0, ΔS°>0, and ∆G°< 0 indicated that dye removal was spontaneous and endothermic in nature. Reuse of the adsorbent in 10 consecutive experiments also showed that removal efficiency was reduced by about 11.94%.Adsorption mechanism can be explained by the presence of a large number of negatively charged carboxyl groups and hydroxyl groups on surface of CNT-Alg-Fe3O4, which could react with colour molecules through electrostatic interactions and π-π dispersive interactions.