Thiol-ene synthesis of thioether/carboxyl-functionalized polymers for selective adsorption of silver (I) ions

Abstract

In this study, a novel adsorbent (TCP) for the selective adsorption of Ag (I) was synthesized by thiol-ene polymerization of dimercaptosuccinic acid and 1,3,5-triallyl-1,3,5-triazine-2,4,6-trione. Element analysis, FT-IR and NMR spectroscopy confirmed that TCP was a functional-group-dense polymer with abundant thioether/carboxyl groups. The results of batch adsorption experiments revealed that the maximum adsorption capacity for Ag (I) by TCP at pH 4 was 5.2 mmol g−1, which was much higher than that at pH 2. Moreover, the adsorption isotherm of Ag (I) on TCP at pH 4 followed the Langmuir model better. However, the isothermal adsorption behavior at pH 2 fitted the Freundlich model well. The kinetic study demonstrated that both chemical adsorption and internal diffusion might be involved in the Ag (I) adsorption process. Furthermore, TCP showed much higher selectivity for Ag (I) in the presence of multiple interfering ions at pH 2 than that at pH 4. However, if the initial concentration of Ag (I) ions was high enough, TCP still exhibited good selectivity for Ag (I) in the presence of Cu (II) over a wide pH range: the selectivity coefficient (KAg/Cu) fluctuated between 40 and 60 in the pH range of 0.5–5. FT-IR spectroscopy and XPS analysis evidenced that the carboxyl and thioether groups in TCP could have synergistic effects on the adsorption of Ag (I), which might form five-membered or six-membered chelated rings, thereby inhibiting the combination of the carboxylic groups with other interfering ions. In addition, TCP showed high adsorption capacity and selectivity for Ag (I) in the treatment of simulated industrial effluent at pH 2.