Recent advances on magnetic biosorbents and their applications for water treatment

Water pollution threatens environment and human health. Common polymer-based sorbents are used to trap pollutants by these sorbents are difficult to separate from treated water and, in turn, their application is limited. Alternatively, nanomaterials with magnetic features offer the advantage of fast and easy magnetically-assisted separation. Moreover, the surface modification of magnetic nanoparticles with biopolymers enhances their adsorptive capabilities. We review recent developments on magnetic biosorbents for water treatment. We present chemical strategies for the surface modification of magnetic nanoparticles with biopolymers to obtain highly effective, robust and reusable biosorbents. This can be done by two strategies: in situ functionalization and post-synthesis functionalization. Post-synthesis functionalization is done in two distinct stages, the synthesis of the magnetic nanoparticles and the surface functionalization, thus allowing better control of each stage individually. Surface functionalization involves either simple coating or the covalent attachment of the biopolymer chains to the surface. Overall, covalent immobilization of the biopolymer onto the particle’s surface is recommended to ensure successful recycling and reuse of the biosorbents without significant loss of adsorption capacity. Finally, we discuss the performance of several magnetic biosorbents in the uptake of heavy metal species and organic pollutants from water.