Advanced green capture of microplastics from different water matrices by surface-modified magnetic nanoparticles

The extensive production and application of plastic in recent decades has resulted in the presence of microplastics (MPs) in different water bodies. Considered as contaminants of emerging concern (CECs), MPs are accessible to a wide range of organisms and can act as vectors for the transport of other persistent organic pollutants. The existing technologies to remove microplastics from wastewaters and prevent their intrusion in nature, still present several limitations, resulting in an urgent need to develop novel, fast, cost-effective and greener alternatives. In this work, the magnetophoretic capture of MPs by their assembly with magnetic nanoparticles through either electrostatic interactions or molecular forces is investigated. For the experimental assessment, magnetic nanoparticles were synthesized by hydrothermal coprecipitation and solvothermal decomposition methods, while polyethylene (PE) microspheres were selected as model microplastic pollutants. As a noteworthy novelty, thermal decomposition and coprecipitation particles were functionalized with amino groups and sodium alginate (SA), respectively, resulting in a modification of their surface properties and enhanced electrostatic or molecular interactions with MPs. After preliminary experiments, a concentration of 1.3 g L-1 and a contact time of 20 min between magnetic nanoparticles and MPs, were selected as operating conditions to assess the influence of the functional groups on the capture performance. The influence of other variables in the process was also evaluated, including the magnetic nanoparticles synthesis method, the pH of the medium, varied in the range 4–8, and the water constituents that may be present in water bodies. Results demonstrated that the presence of different types of polar groups on the surface of the magnetic nanoparticles make them interact towards MPs through electrostatic attraction or molecular forces, considerably enhancing the capture performance of bare magnetic nanoparticles. This work represents a step forward in the development of new and reliable techniques for the environmentally friendly capture of microplastics from polluted waters.