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

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 (R-2 = 1, X-2 = 0.012) and Pseudo-second-order kinetics (R-2 = 0.993, X-2 = 0.015) showed that adsorption process is monolayer and chemical in nature. Delta H degrees> 0, Delta S degrees>0, and increment G degrees< 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 pi-pi dispersive interactions.

Automated summary

In this study, the removal of dye ADMI from raw textile wastewater was investigated using magnetic multi-walled carbon nanotubes-loaded alginate. The key factors, including pH, adsorbent dose, and contact time, were optimized using response surface methodology-based central composite face-centred design. The adsorbents were characterized using various techniques. The developed model fit well with the experimental data, and under the optimized conditions, a high removal efficiency and ADMI adsorption capacity were achieved. The adsorption process was found to be monolayer and chemical in nature. The adsorption mechanism could be explained by the presence of negatively charged carboxyl and hydroxyl groups on the surface of the adsorbent.