Improvement of microalgae harvesting by magnetic nanocomposites coated with polyethylenimine

•Fe3O4–PEI nanocomposites with large amount of NH2 groups were synthesized.•97% of harvesting efficiency for microalgal cells was obtained with the nanocomposites.•Magnetic separation provides a powerful tool for microalgae harvesting in practice.

Fe3O4 nanoparticles were functionally coated with polyethylenimine (PEI), which contained a high concentration of NH2 groups, for the efficient harvesting of microalgae. The functional magnetic nanocomposites were 12 nm in diameter and 69.77 emu/g of saturation magnetization. Using a nanocomposite dosage of 20 mg/L for harvesting Chlorella ellipsoidea cells, a harvesting efficiency of 97% was achieved within 2 min. Increasing the temperature resulted in an increase in harvesting efficiency. The adsorption isotherm data fit the Langmuir model, suggesting that the adsorption was monolayer. The adsorption capacity of the Fe3O4–PEI nanocomposites for the microalgal cells reached up to 93.46 g-DCW/g-nanocomposites through electrostatic attraction and nanoscale interactions between the nanocomposites and the microalgal cells. The functional nanocomposites provide a base for efficient microalgae harvesting with clear advantages such as rapid execution, low energy consumption, and improves water-use in the algal harvesting process.

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