Immobilization of biogenic metal nanoparticles on sustainable materials - green approach applied to wastewater treatment: a systematic review

The application of the principles of green chemistry to the synthesis of metal nanoparticles (MNP) is a new emerging issue concerning sustainability. Together with the green nanotechnology, this is an evolving approach with innovative, reliable and sustainable solutions for applications in all fields of life. Those principles may be used on greener bio-inspired materials applied for the synthesis of MNP as well as for their immobilization on solid supports. This review is carried out for its relevance, covering the available literature on the green fabrication of MNP from different bio-resources, ranging from micro- to macromolecular levels (bacteria, fungi, yeasts, algae and plants) acting as reducing and capping agents and enabling the immobilization of biogenic MNP on sustainable materials to improve their performance when applied to wastewater treatment. Materials derived from renewable and earth-abundant sources (clays, natural zeolites, sediments, sands, rocks and volcanic glasses) or residues from food, industry and agro-forestry activity, activated carbon and biochar were found as sustainable supports with diverse applications such as disinfection of water or removal/degradation of various pollutants of wastewater. For the first time, a thorough review of the literature available on this topic has been carried out and the synthesis and immobilization of biogenic MNP on sustainable materials are reported, through two main routes: (i) bio-inspired fabrication of MNP, with the consideration of the adverse effects of their suspension status and (ii) supported MNP obtained with sustainable supports, with focus on natural or on waste materials, activated carbon and biochar, as well as on the obtained modified sustainable materials. Finally, an economic and environmental perspective as well as the challenges on the use of supported MNP will be presented. The simultaneous use of bio-resources and sustainable materials as reducing/capping agents and supporting materials to obtain supported metal nanoparticles is a significant green approach applied to wastewater treatment.