Adsorption performance of water-floating composites for heavy metal removal in marine and freshwater systems

Abstract

Water-floating adsorbents for removal of heavy metal contaminants have received little attention but could ignite energy efficient technologies for on-site water decontamination applications. The aim of this work is to introduce such adsorbents based on biocompatible polymer matrices. First, we synthesize polymer microparticles via Pickering emulsion polymerization, utilizing environmentally neutral silica nanoparticles as stabilizers dispersed in the water phase. The oil phase contains vinyl pyridine and methacrylic acid as ligands, along with divinylbenzene as a crosslinking agent. The emulsion composition dictates the morphology, resulting in either solid polymer microspheres from O/W emulsions or blob-like microparticles with complex internal structures from mixed W/O/W Pickering emulsions. Next, we systematically compare these two microparticle types for heavy metal ion adsorption of Cu(II), Pb(II), Hg(II), Co(II), and Ni(II) from water, including real marine and freshwater samples spiked to simulate pollution. Adsorption performance differences are analyzed in relation to chemical composition and morphology. Additionally, these microparticles are embedded into a polyvinyl alcohol hydrogel matrix, creating water-floating composites, whose adsorption capacities are also evaluated. This study identifies key physicochemical parameters influencing heavy metal ion adsorption efficiency for both microparticles and hydrogel composites. While composites exhibit slightly lower adsorption capacities than free microparticles their performance remains comparable. The floating nature of these materials makes them attractive for marine decontamination applications, offering a scalable solution for heavy metal remediation in coastal and oceanic environments.