In this research, multi-walled carbon nanotubes (MWCNTs) were functionalized by oxidation with strong acids HNO3, H2SO4, and H2O2. Then, magnetite/MWCNTs nanocomposites were prepared and polystyrene was added to prepare polystyrene/MWCNTs/magnetite (PS:MWCNTs:Fe) nanocomposites. The magnetic property of the prepared nano-adsorbent PS:MWCNTs:Fe was successfully checked. For characterization, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, and BET surface area were used to determine the structure, morphology, chemical nature, functional groups, and surface area with pore volume of the prepared nano-adsorbents. The adsorption procedures were carried out for fresh MWCNTs, oxidized MWCNTs, MWCNTs-Fe, and PS:MWCNTs:Fe nanocomposites in batch experiments. Toluene standard was used to develop the calibration curve. The results of toluene adsorption experiments exhibited that the PS:MWCNTs:Fe nonabsorbent achieved the highest removal efficiency and adsorption capacity of toluene removal. The optimum parameters for toluene removal from water were found to be 60 min, 2 mg nano-sorbent dose, pH of 5, solution temperature of 35 °C at 50 mL volume, toluene concentration of 50 mg/L, and shaking speed of 240 rpm. The adsorption kinetic study of toluene followed the pseudo-second-order kinetics, with the best correlation (R2) value of 0.998, while the equilibrium adsorption study showed that the Langmuir isotherm was obeyed, which suggested that the adsorption is a monolayer and homogenous.
