Functionalized chrysotile nanotubes with mercapto groups and their Pb(II) and Cd(II) adsorption properties in aqueous solution

Chrysotile nanotubes (ChNTs) synthesized under hydrothermal conditions were functionalized by surface grafting in toluene with 3-mercaptopropyltrimethoxysilane (MPTMS). The mercapto functionalized ChNTs (ChNTs-SH) were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and N 2 adsorption–desorption. The adsorption of Pb(II) and Cd(II) on ChNTs-SH was investigated systematically by evaluating the effects of contact time, adsorbent dosage, initial pH and temperature. Initial pH could play an important role on the adsorption of Pb(II) and Cd(II) onto ChNTs-SH. The adsorption kinetics and isotherms of Pb(II) and Cd(II) on ChNTs-SH indicated that the kinetic data of adsorption reactions were well described by the pseudo-second-order model (R 2   =   0.9960 and 0.9970, respectively) and the adsorption isotherms were fitted well by the Langmuir model ( q m Pb(II)   =   83.96   mg/g, q m Cd(II)   =   39.23   mg/g at 298   ±   1   K). The thermodynamic parameters (Δ G , Δ H and Δ S ) indicated that the adsorption process of Pb(II) and Cd(II) on ChNTs-SH was spontaneous and endothermic. ChNTs-SH could obviously improve the adsorption capacity for Pb(II) by 225.4% and for Cd(II) by 123.5% as compared with ChNTs. Overall, ChNTs-SH could provide a potential remedy for heavy metal contamination in wastewater.