Thiol-functionalized multi-walled carbon nanotubes for effective removal of Pb(II) from aqueous solutions

In this study, thiol-functionalized multi-walled carbon nanotubes (MWCNT-SH) was synthesised using carboxy-functionalized multi-walled carbon nanotubes (MWCNT-COOH) as a precursor and 2-mercaptoethanol as a sulfur source. It was an effective adsorbent for Pb(II) removal. The SEM, TEM, FTIR, XPS, EDS, TGA and zeta potential analysis were used to characterize this adsorbent. The adsorption of Pb(II) mainly depends on the abundant functional groups on the surface of MWCNT-SH. Pb(II) adsorption experiments using MWCNT-SH and MWCNT-COOH showed that the adsorption capacity of the former was increased by approximately 30.5% compared to the latter at pH = 5. The increase in adsorption capacity was attributed to the higher adsorption activity of –SH compared to –COOH for Pb(II). The adsorption kinetics data is described well by the pseudo-second-order model, and this implies that the chemical adsorption process mainly determined the adsorption rate. The Pb(II) equilibrium data were highly consistent with the Langmuir adsorption isotherm, and the maximum adsorption capacity for Pb(II) was 144.9 mg g−1. In addition, the adsorption was a thermonegative and spontaneous reaction. It can be verified by thermodynamic research (ΔG < 0, ΔH > 0, ΔS > 0). Finally, Pb (II) removal apply to three kinds of natural wastewater demonstrated the potential of MWCNT-SH. All the results showed that MWCNT-SH has broad application prospects in water treatment. •The grafting of sulfhydryl groups improved the adsorption properties of Multi-walled carbon nanotubes.•The mechanism for the adsorption on adsorbent were elucidated.•Adsorbents showed excellent performance in natural wastewater treatment.