Simultaneous Adsorption of Toxic Dyes onto the Magnetite Decorated Multi-Walled Carbon Nanotubes: Statistical Optimization, Kinetics and Isotherms

In the work, the magnetite decorated multi-walled carbon nanotubes (Fe 3 O 4 /MWCNTs) were employed to simultaneously adsorb methylene blue (MB) and methyl orange (MO) dyes from aqueous media. The experiments were conducted based on a Box-Behnken design (BBD) with the variables of Fe 3 O 4 /MWCNTs dosage (0.8–2.0 g), pH (3–9), contact time (30–50 min) and ionic strength (0.02–0.10 mol L –1 ) using fixed concentrations of the dyes (10 mg L –1 ). The measured process efficiencies were fitted to the second-order response surface models ( R 2 > 0.97) by which the optimum conditions for simultaneous adsorption of the dyes was predicted as: 2.0 g L –1 of nanoadsorbent, contact time of 48.5 min, pH 5 and ionic strength of 0.02 mol L –1 . The experiments conducted at the conditions resulted in the removal percentages of 98.90 ± 0.29 for MB and 96.64 ± 0.22 for MO. Analysis of variance showed that the nanoadsorbent dosage was the most important factor affecting the removal process. The dye-nanoadsorbent systems followed the pseudo-second order kinetic model ( R 2 > 0.99). Moreover, Langmuir and Temkin isotherms were found to be the best models to describe MB and MO adsorption onto Fe 3 O 4 /MWCNT nanoadsorbent, respectively.