Mechanism and application of sulfhydryl-modified chitosan derivative for decontamination of Pb(II) and Cd(II) in water bodies.

The accumulation of lead and cadmium in water bodies is a serious threat to environmental safety and human health, and they must be removed from wastewater. Based on this this study, a novel sulfhydryl-modified chitosan derivative (SHCS) was prepared by grafting method using chitosan as a substrate for the removal of Pb(II) and Cd(II) from polluted water bodies. The results showed that the SHCS derivative was a mesoporous biosorbent with a specific surface area of 0.0505 cm3/g. The adsorption kinetics of the adsorbent on the pollutants conformed to the pseudo-first-order and pseudo-second-order models (R2 > 0.99). The adsorption isotherms all followed the Langmuir model (Pb(II): R2 = 0.9388, Cd(II): R2 = 0.9592). The maximum adsorption capacities of SHCS were 209.27 mg/g and 64.19 mg/g for Pb(II) and Cd(II), respectively. The free energy of adsorption ΔGθ < 0 indicates that the adsorption process is a spontaneous reaction, in which the adsorption of lead is an adsorptive process (ΔHθ > 0) and the adsorption of cadmium is an exothermic process (ΔHθ < 0). The addition of NaNO3 and cations (K+, Ca2+, and Mg2+) did not affect the adsorption process of Pb(II) and Cd(II). The surface complexation and electrostatic attraction mechanisms controlled the decontamination of Pb(II) and Cd(II) by SHCS in water. Most importantly, the SHCS derivative was effective in removing low concentrations of Pb(II) and Cd(II) from three real wastewater samples as well as a simulated electroplating wastewater.