In-situ self-assembly of plant polyphenol-coated Fe3O4 particles for oleaginous microalgae harvesting.

Plant polyphenol (PP), a natural polymer from the Larix gmelinii, was selected as the surfactant to synthesize Fe3O4. The Fe3O4-PP composite was prepared by in-situ self-assembly in solvothermal synthesis, and characterized using FE-SEM, TEM, XRD, FTIR, XPS, TGA, and VSM. The harvesting efficiency of Chlorella vulgaris was investigated under different parameters, including algal organic matter, dosage, and pH. The results showed that the core-shell sphere of Fe3O4-PP (∼150 nm) was coated by ∼50 nm PP with a saturated magnetization of 40.0 emu/g. The Fe3O4-PP could be directly applied to the culture broth (1.5 g dry cell weight/L, pH = 9.03), achieving 93.0% of harvesting efficiency at 20 g/L. Cells were detached from the harvested aggregates by adjusting pH value to 9.80 and with ultrasonication, which achieved 95.6% of recovery efficiency. The recycled Fe3O4-PP showed high stabilities in surface properties, maintaining more than 87.5% of harvesting efficiency after five recycles.