Spatially Confined Conjugation of Enzyme Immobilized Magnetic Nanochains with Poly(Vinylphosphonic Acid) Polymers Using Droplet Reactors for Uranium Extraction

Abstract

The ultrathin liquid films of the continuous phase in high internal phase emulsions (HIPEs) have a nanoscale dimension, and they are interesting nanoreactors to prepare functional sorbents for uranium U(VI) extraction. Here, 71% α-chymotrypsin (CT) was covalently immobilized onto magnetic nanochains to provide functional sites for amide-containing atom transfer radical polymerization (ATRP) initiator, and then spatially confined conjugation of “grafting-from” based enzyme with poly(vinylphosphonic acid) polymers using HIPEs as droplet reactors was designed. As-prepared sorbents (E-EMC-VPA) have saturation magnetization of 14.85 emu g-1, and they could be used as nano stir bars for achieving effective diffusion and boosting the binding activity. Moreover, the denser compact of droplet and thinner aqueous continuous phase are essential for rapid mixing and uniform distribution of reactants, and less binding site defects of E-EMC-VPA may be achieved. The resulting E-EMC-VPA can remove 97.9% of U(VI) at sorbent-to-liquid ratios of 0.286 g L-1, and maximum adsorption capacity is estimated to be as high as 306.2 mg g-1 at pH 8 and 25 °C according to the Langmuir adsorption model. Polymer-enzyme covalent conjugates yield rationally stable interface of E-EMC-VPA between magnetic core and modified chemical moieties. U(VI) adsorption capacity and removal efficiency in the presence of co-occurring ions is 46.28 mg g-1 and 86.8%, respectively, indicating the excellent binding selectivity from complex matrices. Besides, the remarkable reusability of E-EMC-VPA should provide a novel type of magnetic nanocomposite sorbent for practical uranium extraction. The findings of the present work provide nano-scale reactor to alter the phase equilibrium properties and confine morphologies of magnetic nanocomposites without stirring.

Keywords: Spatially confined conjugation, Droplet reactors, Uranium Extraction, Enzyme immobilization, Magnetic nanocomposite sorbent