Synthesis and Characterization of Nano Fe and Mn (hydr)oxides to Be Used as Natural Sorbents and Micronutrient Fertilizers

Abstract

Fe and Mn (hydr)oxides are widely used as contaminant sorbents in water/wastewater systems but their potential use as micronutrient fertilizers is still poorly known. In this research, four nano-metal (hydr)oxides (amorphous Mn oxide (AMO), Fe-Mn binary oxide (FMBO), two-line ferrihydrite (2L-Fh) and goethite) were successfully synthesized and completely characterized (infrared and Mössbauer spectroscopy, X-ray diffraction particle size, specific surface area, point of zero charge). AMO, FMBO and 2L-Fh were introduced to interact with AgNO3 (20.0 µM) and TlNO3 (100.0 µM) diluted solutions for three days to check their potential capability as potential Ag+ and Tl+ adsorbents. AMO and FMBO (4% w/w) were tested as nanofertilizers by arranging a hydroponic bioassay for 35 days on white lupin culture as a Mn-hyperaccumulator plant model. AMO structure was identified as an amorphous mixture of Mn oxides while FMBO was an Fe dopped birnessite. Both materials were efficient in extracting Ag+ and Tl+ although large Mn concentration was released from FMBO to the solutions. AMO and FMBO promoted Fe and Mn nutrition in plants. Synthetic iron chelate (Fe-EDDHA), present in the nutrient dissolution, could be adsorbed onto AMO surface by producing Fe and Mn accumulation in roots and increasing Mn uptake rate without toxicity symptoms. Therefore, AMO and FMBO not only demonstrated their efficiency as adsorbents, but also displayed they would be promising nanomaterials as micronutrient fertilizers.