Harvesting of Chlorella vulgaris using Fe3O4 coated with modified plant polyphenol.

The Chlorella vulgaris harvesting was explored by magnetic separation using Fe3O4 particles coated with the plant polyphenol chemically modified by a Mannich reaction followed by quaternization (Fe3O4@Q-PP). The -N(R)4+ and Cl-N+-C perssad of the Q-PP were linked to the Fe3O4 particles by N-O bonds, as suggested by the X-ray photoelectron spectroscopy spectra. The thermogravimetric analysis displayed the mass percentage of the Q-PP coated on the Fe3O4 surface was close to ~ 5%. Compared with the naked Fe3O4 particles, zeta potentials of the Fe3O4@Q-PP particles were improved from the range of - 17.5~- 25.6 mV to 1.9~36.3 mV at pH 2.1~13.1. A 70.2 G coercive force was obtained for the Fe3O4@Q-PP composite, which demonstrated its ferromagnetic behavior. The use of Fe3O4@Q-PP resulted in a harvesting efficiency of 90.9% of C. vulgaris cells (3.06 g/L). The Fe3O4 particles could be detached from the cell flocs by ultrasonication leading to a recovery efficiency of 96.1% after 10 cycles. The recovered Fe3O4 could be re-coated with Q-PP and led to a harvesting efficiency of 80.2% after 10 cycles. The magnetic separation using Fe3O4@Q-PP included charge neutralization followed by bridging and then colloid entrapment.