Poly(vinylphosphonic acid) grafted hollow microspheres with nanoparticles-stacked polymer shell for uranium selective extraction: Dynamic role translation of ethyl α-cyanoacrylate

Hollow polymer microspheres (MPs) have attracted much attention in the field of separation science and technology due to their low density, high specific surface area, easy chemical modification, and abundant binding sites. However, traditional methods for preparing hollow microspheres typically involve surfactants and expensive templates, which are time-consuming and uneconomical, and are not suitable for large-scale production. Oil-soluble α-ethyl cyanoacrylate (ECA), a highly reactive monomer, has been employed to prepare hollow microspheres efficiently in the current study. Self-stabilizing encapsulation via fast interfacial polymerization of ECA would confer a special Pickering-like emulsion droplet reactor for rapid microcapsule formation. The ECA acts as both a monomer and a Pickering emulsifier during the reaction, in which case the newly formed polyECA (PECA) nanoparticles accumulate at the interface, forming a shell of PECA layer eventually. Excellent mechanical property of the PECA layers prevent droplets from coalescence, resulting in hollow PECA MPs after drying. To provide adsorption sites for chelating of uranyl ions, a water-soluble vinyl monomer grafted with ethylene phosphate (vinylphosphonic acid) was then introduced onto the non-reactive double bonds of the polyECA chain under mild reaction conditions, owning to the slightly amphiphilic nature of the PECA chain. The obtained adsorbent for uranium extraction is thus named as PECA-PO43- MPs. Owing to the accessible affinity sites and hollow structure, PECA-PO43- MPs displayed high adsorption capacities at pH = 7 - 9, showing remarkable selectivity for uranium even in the presence of various competition ions. Moreover, PECA-PO43- MPs exhibited high stability as well as excellent recyclability toward uranium capture after five regeneration cycles. Therefore, this work not only presents a new clue to fabricate novel functional MPs in a high-efficiency way, but also provides a novel platform for efficient uranium extraction.