Pickering Emulsion Polymerization Technology─Toward Nanostructured Materials for Applications in Metal Ion Extractions from Wastewaters

Materials that can quickly remove toxic and heavy metal ions to the recommended levels for drinking water by the World Health Organization are in great demand. While a variety of different polymerization technologies have been proposed for the synthesis of microbeads for adsorbing metal ions, many pose various technical and environmental challenges, requiring several processing steps before deployment. In this work, we employ the Pickering emulsion polymerization technology (PEmPTech), a green water-based technology for facile synthesis of nanostructured micrometer-sized beads carrying ligands, which can extract heavy metal ions from wastewaters. PEmPTech allows for using a cocktail of vinyl-carrying monomers to form stable Pickering emulsions that can be polymerized. The Pickering emulsions are stabilized by glycidyl-functionalized silica nanoparticles by creating a shield of a nanoparticle monolayer on the emulsion droplet surface. After polymerization, nanostructured microspheres are obtained. The adsorption capacities for Cu(II) ions in a series of polymers obtained with this method increase from 2.1 to 31.1 mg/g with an increase in the 4-vinylpyrridine monomer in the composition. From the ions tested for adsorption (Cu(II), Ni(II), and Co(II)), the microbeads have a preference for Cu(II), even in competitive adsorption experiments. Thus, we demonstrate that PEmPTech is a green and viable technology for the synthesis of materials for extraction of metal ions from wastewaters.