Manipulation of Particle Size and Sorption Capability of Nano-Scale Magnetite via Controlling Surface Coating

Non-point source nutrient release from land to water, which leads to the eutrophication and toxic algal blooms in natural water, is not easy to control effectively because in-situ injection of suspended particles is often failed to reach deep soils due to nanoparticles tending to agglomerate into micro particles. In this work, we found that particle sizes of synthetic magnetite nanoparticles (Fe₃O₄) and sorption capacity of phosphate were controllable by manipulating the surface coverage of stabilizer (starch). The sorption density and starch stabilized particle sizes were positive correlation. In order to enhance the stability and dispersibility of the nanoparticles, the particle sizes were reduced to nano-scale with high dosage of starch, which weakened the phosphate sorption capability. To recover the activity of the nanoparticles, α-amylase was employed to degrade the surface coating. The phosphate sorption capacity was almost doubled when α-amylase was applied comparing with that without α-amylase. Column testes indicated that highly stabilized nanoparticles could be delivered to the targeted depth of soil column, and the sorption activity was recovered by the in-situ biodegradation of starch. The technology provides methods for in situ immobilization of phosphorus in over fertilized soils, which is significant in controlling the eutrophication of aquatic environments.