Enhanced Selective Adsorption of Pb(II) from Aqueous Solutions by One-Pot Synthesis of Xanthate-Modified Chitosan Sponge: Behaviors and Mechanisms

Sponge-like xanthate-modified chitosan with a three-dimensional network macroporous structure was prepared using a facile one-pot approach. The as-prepared adsorbent possessed remarkable adsorption capacity and excellent mechanical property as well as rapid and intact separation performance. Adsorption properties of Pb(II), Cd(II), Ni(II), and Zn(II) on xanthate-modified chitosan sponge (XCTS) were systematically investigated in single and multiple systems The experimental data for each heavy metal adsorption well fitted to the pseudo second-order kinetic model and Langmuir isotherm model. The maximum adsorption capacities of Pb(II), Cd(II), Ni(II), and Zn(II) were 216.45, 92.85, 45.46, and 41.88 mg/g, respectively. The mutual interference effects of heavy metals in multiple systems were investigated using the inhibitory effect and equilibrium adsorption capacity ratios. The results indicated that the coexisting metal ions had a synergistic promoting effect on Pb(II) adsorption. The competitive adsorption behaviors of Pb(II) in multiple systems were successfully described by the Langmuir and Langmuir competitive models. The adsorption capacity of Pb(II) in multiple systems was higher than that in single system while those of Cd(II), Ni(II), and Zn(II) had a significant decrease in multiple systems, especially for Ni(II) and Zn(II). It turned out that Pb(II) could be effectively removed from an aqueous solution in the presence of Cd(II), Ni(II), and Zn(II), whereas the removal of Cd(II), Ni(II), and Zn(II) would be restrained by the presence of Pb(II). The high selective factor and physicochemical properties of these studied heavy metals revealed the selective adsorption sequence: Pb(II) > Cd(II) > Ni(II) > Zn(II). The characteristic analyses showed sulfur and nitrogen atoms participated in the heavy metal adsorption. The interaction mechanism between Pb(II) and coexisting metal ions could be attributed mainly to the direct displacement effect.