Ternary nanocomposite of SiO2/Fe3O4/Multi-Walled Carbon Nanotubes for Efficient Adsorption of Malachite Green: Response Surface Modeling, Equilibrium Isotherms and Kinetics

In the work, synthesis and application of the ternary nanocomposite of SiO2/Fe3O4/multi-walled carbon nanotubes (SFCNT) for adsorptive removal of malachite green (MG) from aqueous solutions are reported. A Box-Behnken experimental design with the variables of SFCNT dosage, contact time, pH and ionic strength was used to optimize the effects of the variables on the decolourization process. The results were satisfactorily fitted to a quadratic response surface model with R2=0.9735 and F=36.78 which predicted the optimum conditions of operation (SFCNT dosage of 0.192 g L-1, contact time of 25.1 minutes, pH of 6.26, and 0.03 mol L-1 ionic strength) and the removal efficiency of 98.42±0.18% was achieved. The adsorption data obtained for different MG concentrations showed good agreement with the pseudo-second order kinetic model (R2>0.99). The data were also fitted to different isotherms (Langmuir, Tempkin, Harkins-Jura, Jovanovic, Halsey and Freundlich) and the results of error analyses showed that Freundlich isotherm was the best model to describe the dye-nanocomposite adsorption system.