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.