Enhancing the adsorption performance of carbon nanotubes with a multistep functionalization method: Optimization of Reactive Blue 19 removal through response surface methodology

• A novel functionalization method: Microwave irradiation followed by acid sonication.
• Adsorption capacity enhanced about 400% after the functionalization procedure.
• RSM was applied to simulate/optimize the dye adsorption using functionalized CNTs.
• Eight optimum scenarios were selected and validated by further experiments.

The main aim of present study was to enhance the adsorption capacity of Reactive Blue 19 (RB19) onto multi-walled carbon nanotubes (MWCNTs), pretreated in a multistep functionalization process. The functionalization procedure consisted of microwave irradiation followed by sonication in dilute H2SO4. The properties of MWCNTs were investigated by X-ray diffraction, scanning electron microscopy, N2 adsorption isotherms (Brunauer–Emmett–Teller surface area analysis), Raman spectroscopy and Fourier transform infrared spectroscopy. The effective addition of desired functional groups resulted in a considerable increase of dye removal efficiency and adsorption capacity. For pristine and functionalized MWCNTs, the maximum adsorption capacities were found to be 53.33 and 211.02 mg/g, respectively. In addition to the main aim of this research, a statistical/mathematical approach – response surface methodology – was utilized to simulate and determine the optimum conditions of RB19 removal by functionalized MWCNTs using three selected parameters (adsorbent dose, initial dye concentration and pH). High R2-value (97.75%) and a good agreement between predicted R2-value (89.11%) and adjusted R2-value (95.72%) demonstrated an acceptable proportion of the experimental and predicted results. For maximum RB19 removal efficiency, eight optimum scenarios were also obtained and validated by further experiments.