Selective Capture of Germanium from Water by a Hydrotalcite-Based Ion-Imprinted Polymer: Performance and Mechanism

In this work, a germanium ion-imprinted polymer (Ge-IIP) based on α-bromobutyric intercalation-modified hydrotalcite was synthesized by atom transfer radical polymerization and applied for the capture of germanium ions from wastewater. In particular, layered hydrotalcite as a skeleton support induced in situ polymerization of Ge-IIPs to form graded pores, and an α-bromobutyric interlayer was also used as an initiator to induce graft polymerization of functional monomers of 3-dihydroxypropyl-2-acrylate to form strong coordination cavities for germanium ions. Batch experiment results showed that Ge-IIPs could effectively capture germanium at a pH value of 3, and the maximum adsorption capacity was up to 55.18 mg·g–1. The adsorption kinetics and isotherms indicated that the capture of germanium was consistent with a pseudo-second-order kinetic model and a Freundlich isotherm model. The distribution coefficient values of Ge(IV) adsorption by Ge-IIPs in a coexisting metal ion solution were as high as 25 231.36 mL·g–1, indicating significant capture selectivity. In addition, Ge-IIPs showed good reusability, and the uptake rate of germanium could still reach 98.45% after 5 cycles. Furthermore, density functional theory calculation indicated that the efficient selective capture of germanium by Ge-IIPs may be attributed to the ion exchange and surface complexation between germanium ions and the abundance of o-hydroxyl groups in the Ge-IIP structure. The excellent salt tolerance and adsorption selectivity of Ge-IIPs provide the possibility for its practical application in germanium recovery from wastewater.