Magnetic Carbon Nanotubes-Silica Binary Composite for Effective Pb(II) Sequestration from Industrial Effluents: Multivariate Process Optimization

In this work, magnetic multiwalled carbon nanotubes-silica binary composite (mCNT@APS) is synthesized via amide bond and utilized for the Pb(II) adsorption from aqueous solutions in batch mode. The composite is characterized using Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), X-ray diffraction (XRD), and point of zero charge (pH(pzc)) studies. Three levels and three factorial Box-Behnken design in response surface methodology is employed to assess and optimize the effects of influential parameters: pH, initial concentration, and contact time. Using the desirability function, the obtained optimum conditions are pH 5.4, feed concentration 757 mu g mL(-1) and contact time 4 min. The electrostatic attraction between the active binding sites of adsorbent and Pb(II) at pH(pzc) < pH results in higher saturation capacity (79.69 mg g(-1)) in accordance with the best fitted non-linearized Langmuir isotherm model. The pseudo-second-order model fits well to the kinetic data implying chemisorption of Pb(II) onto mCNT@APS. The material can be regenerated up to 15 sorption-desorption cycles using 5 mL of 1.5 M HNO3. The adsorbent exhibits excellent Pb(II) removal efficiency (>98%) from industrial effluents and tap water samples.

Automated summary

Through the synthesis of magnetic carbon nanotubes-silica composite mCNT@APS, this study achieved excellent adsorption performance for lead, particularly suitable for the removal of Pb(II) from industrial effluents and tap water. The optimized conditions were pH 5.4, feed concentration 757 μg mL(-1) and contact time 4 min, exhibiting high saturation capacity and chemical adsorption characteristics.