Removal of silver and lead ions from water wastes using Azolla filiculoides, an aquatic plant, which adsorbs and reduces the ions into the corresponding metallic nanoparticles under microwave radiation in 5 min

Pollution of water bodies with heavy metal ions is a major worldwide environmental problem. The objective of this study was to elucidate the mechanism in which metallic ions are adsorbed and reduced to metallic nanoparticles onto plant materials using microwave radiation. In this research, we have fabricated metallic silver and lead nanoparticles from their corresponding ions using the aquatic plants Azolla filiculoides and Pistia stratiotes (since identical results are obtained for both plants, the emphasis will be on the Azolla) under microwave radiation. Our data show that metallic silver and metallic lead nanoparticles were completely removed from the polluted solution and were embedded in the A. filiculoides surface after 5 min of microwave reaction. It was also found that, for both metals, reduction of the metallic ions was accomplished by the plant matrix without the need of an external reducing agent. Most of the particles had a spherical shape within the 10-50 nm size range. Mass balance data clearly indicate that most of the silver particles were found on the surface of the plant and not in the clean water. Pectin and α-glucuronic acid did not reduce the silver or lead ions under microwave radiation. We therefore hypothesize that perhaps the proteins or sugar alcohols in the plant matrix were serving as the reducing agents. We believe that this technique in which adsorption and reduction are combined using microwave radiation can be applied for removing and recycling metallic ions from contaminated water and industrial wastewater.