Adsorption of mercury ions from synthetic and real wastewater aqueous solution by functionalized multi-walled carbon nanotube with both amino and thiolated groups

• Process of real and synthetic removal of Hg(II) by functionalized MWCNTs was explored.
• Hg(II) sorption of MWCNTs-SH is remarkably more than MWCNTs, approximately three folds.
• The adsorption isotherm, kinetics and thermodynamics were studied in detailed.
• Adsorption mechanism, desorption and reusability of MWCNTs-SH is investigated.

The functionalization of multi-walled carbon nanotubes (MWCNTs) was achieved by reacting ethylenediamine, cyanuric chloride and sodium 2-mercaptoethanol in sequence as efficient ways to introduce amine and thiol functional groups onto the nanotube sidewalls. The synthesized amino and thiolated MWCNTs were characterized by Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM). A series of batch adsorption experiments were conducted to study the effect of pH, dose of adsorbent, metal concentration and temperature on Hg(II) uptake by the functionalized MWCNTs. The adsorption isotherm data were better fitted by Langmuir model, while kinetic data can be characterized by the pseudo-second-order rate kinetics. Based on the thermodynamic data of ΔH∘, ΔS∘ and ΔG∘ obtained, it can be concluded that the Hg(II) ion adsorption on the functionalized MWCNTs is exothermic, spontaneous and physisorption in nature. In a fixed-bed column adsorption, the effects of bed height, flow rate and initial ion concentration on the breakthrough curve were investigated, on which the predictions were found to be satisfactory both by the Yan and Thomas models. Lastly, we found out the as-synthesized MWCNTs-SH are efficient in Hg(II) removal from real wastewater.