Nanocomposite of carbon nanotubes/silica nanoparticles and their use for adsorption of Pb(II): from surface properties to sorption mechanism

This paper demonstrates the synthesis of multi-wall carbon nanotubes and silica nanocomposite (CNT/SiO₂). Successful realization of MWCNT/SiO₂ nanostructure was observed by scanning electron microscopy, energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy and high-resolution transmission electron microscopy studies. The as-prepared nanocomposite was evaluated as an adsorbent to remove lead, Pb(II), from aqueous solutions. The resulting MWCNT/SiO₂ manifests propitious adsorption performance (~95%) over silica nanoparticles (~50%) and CNTs (~45%). Lagergren’s pseudo-first order, pseudo-second order and intraparticle diffusion models were used to analyse the kinetic data obtained at different initial Pb(II) concentrations. The adsorption kinetic data were described well by the pseudo-second order model with R² of 0.99. The activation energy (E_a) of the adsorption process was calculated as 15.8 kJ mol⁻¹. Adsorption data were described well by the Langmuir and Temkin models. The positive values of both ∆H° (29.4 kJ/mol) and ∆S° (116.8 J/mol K) obtained suggest an endothermic reaction and in increase in randomness at the solid–liquid interface during the adsorption of Pb(II) on the nanocomposite. The negative ∆G° values indicate a spontaneous adsorption process. Elemental dispersive X-ray analysis and mapping confirmed the adsorption of Pb(II) on the nanocomposite surface. The work also highlights the recyclability of the nanocomposite with high efficiencies and supports its potential for environmental applications. It is anticipated that the results bear broad potential in the sorption domain for the design of efficient and reusable adsorbent.